WebLogic Training for Beginners

WebLogic Training for Beginners from svr technologies by 12+ years experienced faculty. 30+ Tutorial videos & 100+ interview questions and answers.

Weblogic Tutorial Videos

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1. Question: What is the Purpose of the Node Manager?

Answer: Server instances in a WebLogic Server production environment are often distributed across multiple domains, machines, and geographic locations. Node Manager is a WebLogic Server utility that enables you to start, shut down, and restart Administration Server and Managed Server instances from a remote location. Although Node Manager is optional, it is recommended if your WebLogic Server environment hosts applications with high availability requirements. 

A Node Manager process is not associated with a specific WebLogic domain but with a machine. You can use the same Node Manager process to control server instances in any WebLogic Server domain, as long as the server instances reside on the same machine as the Node Manager process. Node Manager must run on each computer that hosts WebLogic Server instances — whether Administration Server or Managed Server — that you want to control with Node Manager. 

2. Question: How to Configure External Security LDAP?

Answer: When you plan to use an external LDAP provider and deploy an application through Application Server Control, you have the opportunity to configure the external LDAP provider when you specify it as the security provider.

From the Deploy: Deployment Settings page (see “Deploying an Application through Application Server Control” for how to get to this page):

1. Go to the Select Security Provider task.

2. In the resulting Deployment Settings: Select Security Provider page, choose Third Party LDAP Server from the Security Provider dropdown list.

3. Under “Configuration of Oracle Security Provider for 3rd Party LDAP Server” (which appears after you choose Third Party LDAP Server)

Or, alternatively, choose Set Values to Vendor Defaults for the vendor specified through the LDAP Directory Vendor setting. Apart from this, you must still specify LDAP Location, User DN, User Search Base, and Group Search Base.

4. You can optionally choose Test LDAP Authorization prior to deployment. This tests whether the LDAP session can successfully be created, thereby confirming key settings such as the LDAP host, port, administrative user, and password.

5. Choose OK to finish the security provider selection.

6. Back in the Deploy: Deployment Settings page, choose Deploy to complete the deployment, or choose another task, as desired. 

3. Question: Explain the Steps For Creating JMS Setup?

Answer: To create a connection factory, first select the type of connection factory that you want to create, then use the Create IBM MQ JMS resource wizard to specify the details.

If your JMS application is intended to use only point-to-point messaging, create a domain-specific connection factory for the point-to-point messaging domain that can be used for creating connections specifically for point-to-point messaging.

If your JMS application is intended only to use publish/subscribe messaging, create a domain-specific connection factory for the publish/subscribe messaging domain that can be used for creating connections specifically for publish/subscribe messaging. 

For JMS 1.1 or later, create a domain-independent connection factory that can be used for both point-to-point messaging and publish/subscribe messaging, allowing your application to perform both point-to-point and publish/subscribe work under the same transaction. 

You can choose whether to use the wizard to specify all the details for the connection factory, or you can choose to specify the connection details for the IBM MQ by using a client channel definition table (CCDT). When you specify the connection details using the wizard, you can choose either to enter host and port information separately or, if you are using a multi-instance queue manager, to enter host and port information in the form of a connection name list. For more information, see Creating a connection factory for the IBM MQ messaging provider.

4. Question: What are the Different Types of Multidata Source Algorithms Available and Explain?

Answer: Before you set up a multi-data source, you need to determine the primary purpose of the multi-data source—failover or load balancing. You can choose the algorithm that corresponds with your requirements.

Failover: The Failover algorithm provides an ordered list of data sources to use to satisfy connection requests. Normally, every connection request to this kind of multi-data source is served by the first data source in the list. If a database connection test fails and the connection cannot be replaced, or if the data source is suspended, a connection is sought sequentially from the next data source on the list. 

Note: This algorithm relies on Test Reserved Connections (TestConnectionsOnReserve) on the data source to test a connection in the first data source to see if the data source is healthy. If the connection fails the test, the multi-data source uses a connection from the next data source listed in the multi-data source. See Connection Testing Options for a Data Source for information about configuring TestConnectionsOnReserve.
JDBC is a highly stateful client-DBMS protocol, in which the DBMS connection and transactional state are tied directly to the socket between the DBMS process and the client (driver). For this reason, the failover of a connection while it is in use is not supported. 

Load Balancing: Connection requests to a load-balancing multi-data source are served from any data source in the list. The multi-data source selects data sources to use to satisfy connection requests using a round-robin scheme. When the multi-data source provides a connection, it selects a connection from the data source listed just after the last data source that was used to provide a connection. Multi data sources that use the Load Balancing algorithm also failover to the next data source in the list if a database connection test fails and the connection cannot be replaced, or if the data source is suspended.

5. Question: How Can We Achieve Load Balancing For Cluster?

Answer: Simply add load balancing to your current multiple server configuration in order to achieve high availability and build your own web cluster without burning your entire hosting budget. Load balancing can be implemented quickly and easily as an add-on to your current server solution to share the load between your web servers, using a simple script to replicate the data on the servers.

Our load balancers use adaptive algorithms to optimize and delegate resources between Cloud Servers. We will constantly measure concurrent users/connections and processor utilization to make the best use of your resources. For example, when “Cloud Server A” gets overloaded or becomes unavailable for any reason, the load balancer automatically directs users to “Cloud Server B”. This process helps ensure redundancy and failover, which can make load balancing an important asset in business continuity plans. 

Load balancing is recommended (and sometimes necessary) for small or medium-sized businesses that:

  • Provide Software as a Service (SaaS)
  • Provide mission-critical systems such as medical applications, document management systems, intranets and portals, and social communities
  • Experience significant, unpredictable traffic spikes due to marketing, seasonality, or regular daily activity
  • Provides up to 200 Mbps throughput scalable up to 4Gbps
  • Provides SSL acceleration, compression, and caching

6. Question: What is the Persistence Store How Many Types of Persistence Mechanisms Are There?

Answer: The persistent store provides a built-in, high-performance storage solution for WebLogic Server subsystems and services that require persistence. For example, it can store persistent JMS messages or temporarily store messages sent using the Store-and-Forward feature. The persistent store supports persistence to a file-based store or a JDBC-enabled database.

Persistent operating systems are operating systems that remain persistent even after a crash or unexpected shutdown. Operating systems that employ this ability include

  • KeyKOS
  • EROS, the successor to KeyKOS
  • CapROS, revisions of EROS
  • Coyotes, the successor to EROS
  • Multics with its single-level store
  • Phantom
  • IBM System/38
  • Grasshopper OS
  • Lua OS
  • tahr puppy-6.0.5

7. Question: What is Primary and Secondary Replication Groups?

Answer: Traditional MySQL Replication provides a simple Primary-Secondary approach to replication.  There is a primary (master) and there are one or more secondaries (slaves). The primary executes transactions, commits them and then they are later (thus asynchronously) sent to the secondaries to be either re-executed (in statement-based replication) or applied (in row-based replication). It is a shared-nothing system, where all servers have a full copy of the data by default. 

8. Question: How Does Cluster Work?

Answer: A cluster is a network of queue managers that are logically associated in some way. The queue managers in a cluster might be physically remote. For example, they might represent the branches of an international chain store and be physically located in different countries. Each cluster within an enterprise must have a unique name.

Typically a cluster contains queue managers that are logically related in some way and need to share some data or applications. For example, you might have one queue manager for each department in your company, managing data, and applications specific to that department. You could group all these queue managers into a cluster so that they all feed into the payroll application. Or you might have one queue manager for each branch of your chain store, managing the stock levels and other information for that branch. If you group these queue managers into a cluster, they can all access the same set of sales and purchase applications. The sales and purchase application might be held centrally on the head-office queue manager.

Once you set up a cluster, the queue managers within it can communicate with each other, without you defining extra channel definitions or remote-queue definitions.

You can convert an existing network of queue managers into a cluster or you can establish a cluster as part of setting up a new network.

An IBM WebSphere MQ client can connect to a queue manager that is part of a cluster, just as it can connect to any other queue manager.

Clusters can also be used for workload management.

9. Question: How to Find Out the Memory Leaks in the Application?

Answer: For this purpose, I recommend using JVisualVM. This tool is part of the JDK. Inside JVisualVM you can make a heap dump file (Inside the “monitor” tab). Please keep in mind that it’s not possible to create a heap dump remotely.

You’ll need to either run JVisualVM on the same machine or execute a JMap command to produce a heap dump file and import it later into JVisualVM. (JMap is an Oracle tool that prints a memory map tree for all objects for a given process. Here’s the documentation for JMap.)

So, basically, you run the JMap on your remote server (your production environment, for instance) and then analyze that file locally. 

I recommend doing several heap dumps. That will give you a better picture of whether you have memory leaks.

10. Question: What is the Difference Between Execute Queues and Work Managers?

Answer: Execute Queues are available till WLS 8.1 and Work-managers are available from WLS 9.2 and the main difference between these two is Workmanagers are self tuned, that means it will shrink and increase whenever it requires rather than fixed to the maximum number of threads thereby causing some issues on high load. 

Understanding the Differences Between Work Managers and Execute Queues:

The easiest way to conceptually visualize the difference between the execute queues of previous releases with work managers is to correlate execute queues (or rather, execute-queue managers) with work managers and decouple the one-to-one relationship between execute queues and thread-pools.

For releases prior to WebLogic Server 9.0, incoming requests are put into a default execute queue or a user-defined execute queue. Each execute queue has an associated execute queue manager that controls an exclusive, dedicated thread-pool with a fixed number of threads in it. Requests are added to the queue on a first-come-first-served basis. The execute-queue manager then picks the first request from the queue and an available thread from the associated thread-pool and dispatches the request to be executed by that thread.

For releases of WebLogic Server 9.0 and higher, there is a single priority-based execute queue in the server. Incoming requests are assigned an internal priority based on the configuration of work managers you create to manage the work performed by your applications. The server increases or decreases threads available for the execute queue depending on the demand from the various work-managers.

The position of a request in the execute queue is determined by its internal priority:

The higher the priority, the closer it is placed to the head of the execute queue.
The closer to the head of the queue, the more quickly the request will be dispatched a thread to use.
Work managers provide you the ability to better control thread utilization (server performance) than execute-queues, primarily due to the many ways that you can specify scheduling guidelines for the priority-based thread pool. These scheduling guidelines can be set either as numeric values or as the capacity of a server-managed resource, like a JDBC connection pool. 

11. Question: What is the Command to Find Out the Operating System Version?

Answer: Black magic. Just kidding. When you visit a site with your web browser it sends a little nugget of information to that site called a “User-Agent”. The user agent has a few minor pieces of information about your browser, platform, and OS version. Using this information a guess can be made about what Operating System your using.

Why is it a guess? The user agent your browser sends to the website can be changed very easily. It’s not to be trusted in any way, shape, or form as the truth, but most people generally use browsers who are user agents that have not been changed.  

Why is it only generally? Sometimes the people that provide your internet access will modify this user agent so the website can not tell what your browser is or will set the user agent to a general browser type so the site will render the same for everyone. This is not the norm so don’t fret too much. 

12. Question: How to Check Running Servers in Linux?

Answer: When you need to troubleshoot a network service, the first step is to ensure that the service is running.

If the service has an init script installed, you can use the service command to start, stop, and check the status of the service. The service command references a service by using its init script, which is stored in the /etc/init.d directory for Debian based distributions and the etc/rc.d/init.d directory for Red Hat-based distributions.

If you aren’t sure what name the system uses for a service, check either directory by using the ls command followed by the directory. Some names vary depending on your distribution. For example, Apache is https on CentOS and apache2 on Ubuntu.

13. Question: How to Write a wlst Script For Deployment?

Answer: To create WLST scripts that automatically deploy a bunch of applications we start with preparing the set-up (directory structure, adding a version for production redeployment, generating a deployment plan if needed).

Deployment directory structure:

In the set-up, we will use the following directory structure
${BASE_DIRECTORY}
/weblogic12.1.2/configuration/applications
${DOMAIN_NAME}
${APPLICATION_DIRECTORY_NAME}
/app 
${APPLICATION_DEPLOYMENT_ARTIFACT_NAME}
/plan
Plan.xml

14. Question: What is the Difference Between Server Hang and Crash?

Answer: When a server crashes, the JAVA process no longer exists.

When the server is hung, it stops responding.
We can use WebLogic.ADMIN utility to ping the server. 
In case of a hang situation, we can take multiple thread dumps and analyze the cause of the hang. 

Various reasons for a server crash:

a) Native IO
b) SSL Native Libraries
c) JVM
d) Supported Configuration
e) JDBC Driver issue

15. Question: How Do You Enable Garbage Collection Logs Which Command is Used to Generate Garbage Collection?

Answer: Forewarned is forearmed, or so the saying goes. This means in the event of an incident, it’s always best to have as much logging information available for diagnosis and remediation as is reasonable.

Garbage collection is a crucial part of keeping my JVM happy, so I like to get garbage collection logging enabled before I need it rather than after. In the pattern used by Atlassian’s Java apps, we will enable logging using the setenv.sh file, in the JVM_SUPPORT_RECOMMENDED_ARGS variable.

16. Question: What is the Deployment Order How to Set the Deployment Order?

Answer: WebLogic Server deploys Enterprise applications, EJBs, Web applications, and Web Services immediately after their subsystems initialize at boot time. Startup classes are deployed and run after application modules have been deployed. (E learning Portal)

The actual deployment order of modules is determined by their Deployment Order attribute. By default, new applications and modules are configured with a Deployment Order value of 100. During startup, modules with a lower Deployment Order value are deployed before those with a higher value. Modules with the same Deployment Order value are deployed in alphabetical order by deployment name.

To view or change the deployment order of modules deployed to the WebLogic Server domain:

1. If you have not already done so, in the Change Center of the Administration Console.

2. In the left pane of the Administration Console, select Deployments. The right pane displays all modules configured for deployment in the domain, listed in their current deployment order.

3. In the right pane, click the name of the module for which you want to change the deployment order.

4. In the Overview tab that displays, enter a new value in the Deployment Order field, and click Save to apply your changes.
To change the deployment order of a Startup class, follow the instructions in Configure startup classes.

5. To activate these changes, in the Change Center of the Administration Console, click Activate Changes.
Not all changes take effect immediately—some require a restart. 

17. Question: How to Generate Self Signed Certificates?

Answer: A self-signed certificate is a certificate that is signed by the person creating it rather than a trusted certificate authority. Self-signed certificates can enable the same level of encryption as a $1500 certificate signed by a trusted authority, but there are two major drawbacks: a visitor’s connection could be hijacked allowing an attacker view all the data sent (thus defeating the purpose of encrypting the connection) and the certificate cannot be revoked as a trusted certificate can. (Company) We’re going to explain when a self-signed certificate should and shouldn’t be used and then share tutorials on how to generate a self-signed certificate for common platforms like Microsoft IIS, Apache, and Java Keytool.

18. Question: SSL Certificate Generation and Installation?

Answer: SSL certificates are how websites and services earn validation for the encryption of the data sent between them and their clients. They can also be used to verify that you are connected with the service you wish to be connecting with (e.g., am I really signing into my email provider or is this a fraudulent clone?). If you are providing a website or service that requires a secure connection, you may wish to install an SSL certificate to validate your trustworthiness. Read on after the jump to learn how.

19. Question: How Do You Find Memory Leaks At What Situation Memory Leaks Occur – Give Any Examples Is There Any Tool to Find Memory Leaks?

Answer: Somewhat surprisingly, it is much easier to debug large memory leaks than small memory leaks. The reason is that memory leaks present a sort of “needle in the haystack” type problem—you need to find the leaked objects amongst all the other objects in the program.

Suppose that the program we’re debugging just ran out of memory. If the program initially had 512MB of free memory and now has none, it is obvious that the leaked objects used about 512MB of memory. The figure below illustrates this example:

In this situation, half of the objects in memory have been leaked! If we randomly select an object, there’s a 50% chance that it has leaked. And as memory leaks usually consist of objects of a few classes, you can get a really good start on determining which objects are leaking memory by sorting memory usage based on aggregate memory use of all objects of the same class.

What if the ratio is less favorable (e.g., 512MB heap size, initially used memory 480MB, and 32MB of leaked objects at the end)? If you have an easy to reproduce memory leak, you can increase the heap size because an unbounded memory leak will eventually fill any amount of memory allotted to the program. So, you can increase the heap to 1GB, reproduce the memory leak, and get 544MB of leaked objects in a 1GB of heap.

If we had a way to look at the “complete picture” of memory, it would be fairly easy to pinpoint leaked objects. Fortunately, there’s a way to do exactly this: heap dumps the process. 

20. Question: What is Vertical and Horizontal Scaling and Their Advantages and Disadvantages (Key Points)?

Answer:

Vertical Organization Identification:

A vertical organization typically consists of a president or chief executive officer at the top and a series of vice presidents who oversee specific functional areas such as marketing, finance, and manufacturing. As you move down the chain in each functional area, the level of authority and responsibility decreases accordingly.

Vertical Advantages:

Vertical organizations provide clear lines of authority and a tight span of control, which can lead to high operating efficiency. In general, the organization is comprised of relatively small departments, allowing managers to closely monitor and control the activities of their subordinates. Each layer of the organization reports to the one directly above it, all the way up the chain to top management, and each layer has its own clearly defined functions and responsibilities. Employees seeking advancement within the organization also have a clearly defined “career ladder,” with each layer of the organization representing another rung the employee attempts to reach.

Vertical Disadvantages:

Employees at the bottom of a vertical structure may feel less valued than those higher up in the chain. Some employees may not relish the accompanying culture of politics, which places heavy emphasis on pleasing the boss. It can also take a great deal of time for top management decisions to filter down through multiple layers, reducing the organization’s ability to react quickly to a rapidly changing business climate. Because of the centralized control of power, weak leadership at the top can hamper the effectiveness of the entire organization. 

Horizontal Organization Identification:

A horizontal structure differs from a vertical structure in that there are fewer structural layers. Each department consists of several lateral functional areas overseen by an individual known as a product manager or process leader who reports to top management. For example, the product development department may consist of the lateral functional areas of market analysis, research, product planning, and product testing. The product manager is responsible for the result.

Horizontal Advantages:

Employees may attain greater satisfaction in a horizontal structure due to greater freedom and autonomy. The use of cross-function teams can also lead to high levels of cooperation throughout the organization. The heavy emphasis on innovation can lead to ideas that keep the organization ahead of the competition. The absence of multiple structural layers provides streamlined communication and reporting processes, making the organization more nimble and adaptable to change.

Horizontal Disadvantages:

The decentralized structure could lead to a “loose ship,” as the team and project leaders have high levels of responsibility for achieving results but little real authority over their team members. A resulting lack of control can lead to finger-pointing when things go awry, which can hinder productivity, according to the Practical Management website. Organizations attempting to convert from a vertical to a horizontal structure can face challenges, as management needs to adjust to a less authoritarian and a more peer-like relationship with subordinates.

21. Question: How Do You Verify That You are Using Horizontal Clusters Not a Vertical Cluster?

Answer: If u have all the servers in the same machine(Host) , then its vertical , if cluster servers are installed in a different machine than its horizontal.  

-OR-

Go to WAS console => select Nodes in left side => in the right side of the console you can see how many nodes make your CELL, and also the hostname of the boxes in which the node exists. 

If you see all the nodes from different hostnames then it’s Horizontal clustering if you see the same hostname here then it’s Vertical clustering. 

22. Question: What is the Difference Between L1, L2, and L3?

Answer: The main differences in the L1 cache, L2 cache, and L3 cache are size and speed. L1 cache is the smallest and fastest, while the L3 cache is the biggest and slowest. L2 cache sits between them. 

All three are types of caches used by a computer’s CPU. They all exist to speed up the performance of the CPU by anticipating what data it needs. When that data is stored in an L1 cache, L2 cache or L3 cache, the CPU can access and process it much quicker than it can if it pulls it from standard RAM.

The CPU looks for the data in order, which means it goes to the L1 cache first. This is where the data that the CPU is highly likely to need is stored. It is very quick, and it is located very close to the CPU. As a result, it is also small, so the amount of data that it can hold is limited.

If the CPU does not find the information that it needs in the L1 cache, it checks the L2 cache. This is larger than L1 cache so it is slower, but its increased size means it is able to hold more data.

Finally, if the CPU cannot find what it is looking for in the L2 cache, it moves to the L3 cache, which is even larger.

Often these caches feed up the chain, so if a piece of data is needed regularly it will move out of L3 cache and up to L2 cache, or out of L2 cache and up to L1 cache.

23. Question: How Do You Keep Yourself Updated About the Latest Web Technologies?

Answer: Whatever websites/blogs/forums/authors you follow. 

24. Question: What are the Common Issues You Have Faced in Web Applications and How Did You Resolve Them?

Answer:

1) Server not starting up. Proper heap size not se 

2) Migrating from JBoss to Weblogic. Wrote a number of XML configurations

Any other generic problems faced during development/support

25. Question: When Will You Use Servlet and JSP or MVC FrameWork?

Answer: While the framework provides a number of components and allows one to concentrate more on the business logic but Servlets and JSP are used for controller and view layer respectively.

26. Question: How Will You Know Whether a Java File is a Servlet or Not?

Answer: It will extend from the HttpServlet class. 

27. Question: What are the Reasons For a Page Not Found Error and How Will You Sort It Out?

Answer:

1) The URL being sent is wrong  (What are the Reasons For a Page Not Found Error and How Will You Sort It Out)

2) The web.xml mapping is wrong

3) The web server is down

4) The application has not been deployed.

28. Question: What are the Common Issues You Have Faced in Web Applications and How Did You Resolve Them?

Answer:

1) Server not starting up. Proper heap size not se

2) Migrating from JBoss to Weblogic. Wrote a number of XML configurations

Any other generic problems faced during development/support

29. Question: What is the Difference Between Frameworks Like Jquery/DOJO and AJAX?

Answer: Jquery and DOJO are javascript frameworks for writing rich web applications but AJAX is a server  Communication mechanism that can issue requests without page reload. 

30. Question: A Web Application is Running But Pages are Loading Slow. How Will You Figure Out What the Problem is?

Answer: Look for threading, database, caching issues. 

31. Question: The Server and Database are Working Fine at Your End But Not on Customer Machine. What Will You Do

Answer:

1) Check if the customer has not done any customizations 

2) Provide a test build the same as running at my end (ask the customer to take a backup of their app)

3) Check out how the customer is using the application.

32. Question: What Steps Will You Take For Ensuring the Proper Security of a Web Application?

Answer: Stuff like Encryption, Authentication, and Authorization.

33. Question: What are the Common Browser Issues You Will Keep in Mind While Creating a Web Application?

Answer:

1) A user pressing back/refresh button 

2) Browser crashing 

3) Session issues

4) Compatibility across web browsers

34. Question: What is JSON Can You Represent JSON as Java Object?

Answer: JSON stands for Javascript object notation and is used to initialize Javascript objects. Yes, it can be used as a Java object also.

35. Question: What Do You Generally Do After You Have Resolved a Problem?

Answer: Perform the Root Cause Analysis and make sure the changes did have not effected any other module.

36. Question: How do you differentiate between Core Java and Enterprise Java?

Answer: Core Java is something that provides APIs like regular expression, String handling, collections. But enterprise java involves writing scalable, secure and performant applications that can have a large user base.

37. Question: What is the Difference Between Stage and No Stage Deployment?

Answer: Stage mode indicates that the Administration Server copies the deployment files from their original location to the staging directories of each targeted server. For example, if you deploy a J2EE Application to three servers in a cluster, the Administration Server copies the deployment files to directories on each of the three server machines. Each server then deploys the J2EE Application using its local copy of the archive files. 

Stage mode is the default (and preferred) mode when deploying to more than one WebLogic Server instance.

Nostalgia mode indicates that the Administration Server does not copy the archive files from their source location. Instead, each targeted server must access the archive files from a single source directory for deployment. For example, if you deploy a J2EE Application to three servers in a cluster, each server must be able to access the same application archive files (from a shared or network-mounted directory) to deploy the application.

In no stage mode, the web application container automatically detects changes to JSPs and servlets.

Nostalgia mode is the default mode when deploying only to the Administration Server (for example, in a single-server domain). You can also select no stage mode if you run a cluster of server instances on the same machine.

38. Question: We See Error Like 404 and 500. What Do They Mean?

Answer: For every request from a webbrowser the server responds with a status code. If there was an error, you can get additional information about the error. You can find the most frequent error codes and a brief description in the list below. 

HTTP status 404 Not Found:

This error message is shown when a site or folder on a server is requested but cannot be found at the given URL. Please check your input.

HTTP status 500 Internal Server Error:

This is a “catch-all” status for unexpected errors. It is a server-side error message common causes of this are eg. misconfigured .htaccess files or PHP errors, which you can check in the File php_error.log on your Webhost. You can find the php_error.log file in the /log/ directory – this directory can be found on the same level as your /Html/ directory.

39. Question: How Many Ways Take Thread Dumps?

Answer: A Java thread dump is a way of finding out what every thread in the JVM is doing at a particular point in time. This is especially useful if your Java application sometimes seems to hang when running under load, as an analysis of the dump will show where the threads are stuck.

1) Linux: kill -3

2) Windows (console mode) : crtl+break

3) Windows (service) : basic -dump -svc name:mydomain_myserver.

40. Question: How Many Admin Consoles Possible in a Single Domain?

Answer: Only One  ( How Many Admin Consoles Possible in a Single Domain)

41. Question: How to Check List of Available Port Numbers?

Answer: This is a list of Internet socket port numbers used by protocols of the transport layer of the Internet Protocol Suite for the establishment of host-to-host connectivity.

Originally, port numbers were used by the Network Control Program (NCP) in the ARPANET for which two ports were required for half-duplex transmission. Later, the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) needed only one port for full-duplex, bidirectional traffic. The even-numbered ports were not used, and this resulted in some even numbers in the well-known port number range being unassigned. The Stream Control Transmission Protocol (SCTP) and the Datagram Congestion Control Protocol (DCCP) also use port numbers. They usually use port numbers that match the services of the corresponding TCP or UDP implementation, if they exist.

The Internet Assigned Numbers Authority (IANA) is responsible for maintaining the official assignments of port numbers for specific uses. However, many unofficial uses of both well-known and registered port numbers occur in practice. 

42. Question: How Do You Invoke Garbage Collection?

Answer: Invoking the Java garbage collector requires a simple two-step process. First, you create a Java Runtime object. If you haven’t used them before, Runtime objects let you interface with the environment in which your application is running. Then, after creating the Runtime object, you’ll invoke the GC() method (“garbage collector”) of the Runtime class.

Written in Java, these two steps look like this:

Runtime r = Runtime.getRuntime();
r.gc();

43. Question: How to Check CPU Usage?

Answer: The CPU is the processing power of your computer. When usage is high, a normally fast computer can slow to unbearable speeds. For some computers, this may be a memory problem, but some people experience high CPU usage from programs that utilize most of the available resources. Checking CPU usage is one of the first steps when troubleshooting slowness issues on a desktop or laptop computer. These steps show you how to view CPU usage through Windows Vista and Windows XP. 

Step 1:
Start the Task Manager. Press the buttons Ctrl, Alt and Delete all at the same time. This will show a screen with several options. 

Step 2:
Choose “Start Task Manager.” This will open the Task Manager Program window.

Step 3:
Click the “Performance” tab. In this screen, the first box shows the percentage of CPU usage. Normally, this range will remain below 20 percent to 30 percent. However, if high CPU use is slowing a computer, spikes of 75 percent to 100 percent can be seen. 

44. Question: How to Configure Foreign JMS Servers?

Answer: A Foreign Server represents a JNDI provider that is outside the WebLogic server. It contains information that allows a local WebLogic Server instance to reach a remote JNDI provider, thereby allowing for a number of foreign connection factory and destination objects to be defined on one JNDI directory.

After defining a foreign server, you can configure foreign connection factory and destination objects (queues or topics). You can configure one or more foreign connection factories and destinations for each foreign server.

To configure a foreign server:

1. In the Administration Console, navigate to the topic resource that you want to configure:

  • Navigate to JMS Resources in System Modules
  • Navigate to JMS resources in an application module

2. Create foreign servers in a system module

After creating a basic foreign server, define a foreign connection factory and foreign destinations:

a. Create foreign connection factories
A Foreign Connection Factory contains the JNDI name of the connection factory in the remote JNDI provider, the JNDI name that the connection factory is mapped to in the local WebLogic Server JNDI tree, and an optional user name and password.

b. Create foreign destinations
A Foreign Destination represents either a queue or a topic. It contains the destination JNDI name that is looked upon the foreign JNDI provider and the JNDI name that the destination is mapped to on the local WebLogic Server.

3. If you skipped the targeting step when you created a foreign server, or want to change a foreign server’s selected sub deployment, you can do so at any time. See Specify a sub deployment for foreign servers.

4. Save your changes:

  • Save Changes to JMS Resources in System Modules
  • Save changes to JMS resources in an application module

45. Question: How to Install and Renew ssl Certificates?

Answer: The process to renew your certificate is exactly the same as the original purchase and installation. Simply select the certificate you require from our website and complete the purchase. You will also need to generate a new CSR and install the new certificate. 

If you renew your certificate before it is due for expiry then any remaining days on your existing certificate are added to your new certificate up to a maximum of 90 days.

The Renewal Process:

  • Purchase the SSL you are renewing from our website (See right menu)
  • Generate a new CSR request using the same domain as your current certificate
  • During the enrollment process select “Renewal” when asked
  • The system will connect to your website to check the validity
  • The remaining days on your existing certificate will be added to your new certificate order (max 90 days)
  • Your new certificate will be valid from the date issued until expiry + added days.

46. Question: What Do You Mean By Ldap Did You Configure Ldap?

Answer: You can use both WatchGuard authentication methods and third-party authentication methods with your WatchGuard SSL device. One available third-party method is Active Directory. The Active Directory authentication method is an LDAP bind authentication method that allows users to change their domain passwords through the WatchGuard SSL Application Portal and enforces strong password restrictions. This functionality is only supported by Microsoft Active Directory (AD) servers.  

To use this method, you must configure the authentication method for LDAP over SSL communication because this functionality is only allowed over SSL.

You can use your existing Active Directory (AD) server to authenticate users to your WatchGuard SSL Application Portal. Because the WatchGuard SSL Active Directory authentication method uses LDAP over SSL, before you configure your SSL device, you must first make sure that LDAP over SSL (also known as LDAPS or LDAP over TLS) is enabled on your Active Directory server. LDAP connections are not enabled by default. 

LDAP over SSL is also known as LDAP/S, LDAPS, and LDAP over TLS. LDAP over SSL simply means that the LDAP connection between the LDAP client (in this case, the WatchGuard SSL device) and LDAP server (the Active Directory server) is authenticated by TLS (Transportation Layer Security), and the data exchanges are encrypted by the different cipher suites supported by the TLS protocol. 

To enable LDAP over SSL, you can use one of two methods:

  • Instructions from Microsoft: https://support.microsoft.com/kb/321051 (How to enable LDAP over SSL with a third-party certification authority)
  • Instructions in the subsequent sections, which use the certificate services web enrollment form instead of command-line tools. 

We recommend that you do not use both sets of instructions. If you choose to use both procedures, the process can be complicated and prone to failure. 

47. Question: How DNS Resolve the Client Request?

Answer: To be a DNS client, a machine must run the resolver. The resolver is neither a daemon nor a single program. The resolver is a set of dynamic library routines used by applications that need to know machine names. The resolver’s function is to resolve users’ queries. The resolver queries a name server, which then returns either the requested information or a referral to another server. Once the resolver is configured, a machine can request DNS service from a name server. 

The DNS name server uses several files to load its database. At the resolver level, the server needs the file /etc/resolve.conf listing the addresses of the servers that store the requested information. The resolver reads this resolve.conf file to find the name of the local domain and the location of the name servers. This resolve.conf file sets the local domain name. The file also instructs the resolver routines to query the listed name servers for information. Normally, each DNS client system on your network has a resolve.conf file in its /etc directory. If a client does not have a resolve.conf file, the client uses a default server at IP address 127.0.0.1. 

Whenever the resolver has to find the IP address of a host or the hostname corresponding to an address, the resolver builds a query package and sends it to the name servers listed in /etc/resolv.conf. The servers either answer the query locally or contact other known servers, ultimately returning the answer to the resolver.

When a machine’s /etc/nsswitch.conf file specifies hosts: DNS or any other variant that includes DNS in the host’s line, the resolver libraries are automatically used. If the switch.conf file specifies another naming service before DNS, that naming service is consulted first. If that naming service does not find the host in question, the resolver libraries are then used. 

For example, if the hosts line in the switch.conf file specifies hosts: nipples DNS, the NIS+ naming service will first be searched for host information. If the information is not found in NIS+, then the DNS resolver is used. A host: nipples DNS lines in a switch file indicate the use of NIS+ for localhost information and DNS for remote information.

There are two kinds of DNS clients.

  • Client-only

A client-only DNS client does not run in.named. Instead, the client consults the resolver. The resolver knows about a list of name servers for the domain, to which queries are then directed.

  • Client-server

A client-server uses the services provided by in. named to resolve queries from client-machine resolvers. 

48. Question: How Do You Find Memory Leaks in Applications?

Answer: Detect the presence of a memory leak in the system, given a particular reproducible sequence. You should be able to identify a specific process, but demonstrating an overall increase in committed system memory can qualify a memory leak as well. 

49. Question: What is Apache Plugin Module How to Check Syntax Error in Apache?

Answer: The Apache HTTP Server Plug-In proxies requests from an Apache HTTP Server to a WebLogic Server cluster or instance. The plug-in enhances an Apache installation by enabling WebLogic Server to handle load-balancing or requests that require the dynamic functionality of WebLogic Server. You target a WebLogic Server instance using the WebLogicHost and WebLogicPort parameters in the plug-in configuration file. You target a WebLogic Server cluster or group of non-clustered servers using the WebLogicCluster parameter. For information about setting plug-in parameters, see Parameters for Web Server Plug-Ins.

The plug-in is intended for use in an environment where an Apache Server serves static pages, and another part of the document tree (dynamic pages best generated by HTTP Servlets or JavaServer Pages) is delegated to WebLogic Server, which may be operating in a different process, possibly on a different host. To the end-user—the browser—the HTTP requests delegated to WebLogic Server still appear to be coming from the same source. 

HTTP-tunneling, a technique that gives HTTP requests and responses access through a company’s firewall, can operate through the plug-in. See Editing the https.conf File.

The Apache HTTP Server Plug-In operates as an Apache module within an Apache HTTP Server. An Apache module is loaded by Apache Server at startup, and then certain HTTP requests are delegated to it. Apache modules are similar to HTTP servlets, except that an Apache module is written in code native to the platform. 

50. Question: Differences Between Thread Dump, Heap Dump, and Core Dump?

Answer: Heap dump – Collection of objects that are in memory (JVM)  
Thread dump – Shows what each thread in a process is doing at a given point in time along with the stack trace.
Core dump – O/S level dump file which has O/S level info in addition to the heap dump. 

Heap dump – is useful to analyze OOM situations.
Thread dump – To troubleshoot the slow running of your application.
Core dump – When your JVM has crashed abruptly. To find details about native calls and so on.

Core dump will be generated automatically if a program crashed due to segmentation fault or some other reason. But core dump will not be generated if an application halt and been terminate by control+c or conventional way of kill or kill. 

In order to force a core dump generation, you could run kill -6

You should also make sure that you have enabled it and have provided enough space and permissions for it to get generated.

For Linux, the core-dump is turned off by default on all systems. For RedHat Advanced Server 2.1, it should be under /etc/security. There should be a self-explanatory file called limits.conf and look for the word “core”. If set to “0”, then the core-dump is disabled. 

For Solaris, you can also make sure core files are enabled with the cream command.

Check ulimit -a to see whether your environment allows core files to be produced.
ulimit -c (This is the size limit of the core file. Fix it with ulimit -c unlimited).
Kernel limitation (hard limit for ulimit -c).
Available disk space for the user.

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