Oracle Weblogic Server CLASSPATH

Setting up CLASSPATH in Weblogic Server:

Oracle WebLogic Server installs the following script that you can use to set the classpath that a server requires

• WL_HOME/server\bin/setWLSEnv.cmd (on Windows)
• WL_HOME/server/bin/setWLSEnv.sh (on UNIX)

In addition, WebLogic distribution server includes shell scripts that you can use to start the server. These scripts, which are located in the domain directories under the config directory of your WebLogic Server distribution, automatically set up the CLASSPATH variable in the shell before starting the server.

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WebLogic Server Load Balancing

Load Balancing in WebLogic Server 

Load balancing is about distributing work across multiple servers within a cluster. Ideally you want this work to be distributed evenly, to the capabilities and load on each server within the cluster. WebLogic is able to load-balance requests to members within a cluster when certain conditions are satisfied.

First, WebLogic requires that (most) components be deployed homogeneously to each server in the cluster. In the multi-tier application setup, the web application is targeted to all servers that belong to the presentation tier cluster. Because of this, incoming requests can be distributed evenly across the different members of the presentation tier. Similarly, the EJB components are available on all members of the object tier cluster. Because of this, incoming EJB calls from the presentation tier (or any external client) can be distributed across the different servers in the object tier.

When a component is deployed to a cluster, multiple copies of the component will be sitting on the different servers comprising the cluster. WebLogic uses the cluster-wide JNDI tree to record the availability of these replicas in the object tier, whereas a proxy plug-in typically holds the information about the availability of servers hosting the servlets and JSP pages.

WebLogic also must be aware of the status of the components that have been deployed to the cluster. This information forms the basis on which a load balancer can decide which server instances should be used when a request is made to the cluster. WebLogic uses a variety of methods to determine the health status of servers, including multicast heartbeats. By knowing when a server instance is under heavy load while the others aren't, a load balancer is able to direct new requests to the other members of the cluster. Hardware load balancers often have this capability

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WebLogic Clustering

Clustering  in WebLogic

A WebLogic domain can be composed of a number of WebLogic instances, and several of these servers may be grouped into clusters. The Domain is the parent of a Cluster. It contains typically one Admin and one or more Managed servers. Now the Cluster is a grouping of some or all of these managed servers within the domain.For instance, you could set up a cluster of WebLogic servers, all of which host your web application and related resources. This cluster of servers could be fronted by a load balancer that distributes requests evenly across all the members of the cluster. The load balancer could itself be another WebLogic instance. All server instances must belong to the same WebLogic domain. 

Thus, a WebLogic cluster is a group of servers working together with services, such as clustered JNDI, to provide support for failover and load balancing. A domain may in turn have a number of WebLogic instances, several groups of which can be placed into different clusters.

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WebLogic Server Deployment Modes

Staging Modes in WebLogic Server

Stage mode

The Administration Server copies the archive files from their source location to a location on each of the targeted Managed Servers that deploy the archive. Consider if you deploy a J2EE Application to three servers in a cluster, the Administration Server copies the application archive files to each of the three servers. Each server then deploys the J2EE Application using its local copy of the archive files.

* Stage mode is the default mode when deploying to more than one WebLogic Server instance.

External Stage mode

External stage mode is similar to stage mode, but in that the deployment files must reside locally to each targeted server. Here Administration Server does not automatically copy the deployment files to targeted servers in external stage mode, instead we must manually copy the files, or use a third-party application to copy the files for you.

NoStage mode

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. 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.

* Nostage mode is the default mode when deploying only to the Administration Server (for example, in a single-server domain). You can also select nostage mode if you run a cluster of server instances on the same machine.

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Weblogic Server T3 Protocol

T3 is BEA's proprietary protocol. T3 provides a framework for WebLogic Server messages that support for enhancements. These enhancements include abbreviations and features, such as object replacement, that work in the context of WebLogic Server clusters and HTTP and other product tunneling.

Weblogic's implementation of the RMI specification uses a proprietary T3 wire-protocol. javasoft's reference implementation of RMI uses a proprietary protocol called JRMP. weblogic developed T3 because they needed a scalable,efficient protocol for building enterprise-class distributed object systems with java.

T3 is mandated between WebLogic Servers and between programmatic clients and a WebLogic Server cluster. HTTP and IIOP are optional protocols that can be used to communicate between other processes and WebLogic Server. It depends on what you want to do. For example, when you want to communicate between n A browser and WebLogic Server-use HTTP
n An ORB and WebLogic Server-IIOP.

T3 predates Java Object Serialization and RMI, while closely tracking and leveraging these specifications. T3 is a superset of Java Object. Serialization or RMI, anything you can do in Java Object Serialization and RMI can be done over T3.

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Weblogic Interview Questions &FAQ's -2

Weblogic Application Server FAQ's - 2

How many WebLogic Servers can I have on a multi-cpu machine?

There are many possible configurations and each has its own advantages and disadvantages. BEA WebLogic Server has no built-in limit for the number of server instances that can reside in a cluster. Large, multi-processor servers such as Sun Microsystems, Inc. Sun Enterprise 10000, therefore, can host very large clusters or multiple clusters.

In most cases, WebLogic Server clusters scale best when deployed with one WebLogic Server instance for every two CPUs. However, as with all capacity planning, you should test the actual deployment with your target web applications to determine the optimal number and distribution of server instances.

How can I set deployment order for applications?

WebLogic Server allows you to select the load order for applications. WebLogic Server deploys server-level resources (first JDBC and then JMS) before deploying applications. Applications are deployed in this order: connectors, then EJBs, then Web Applications. If the application is an EAR, the individual components are loaded in the order in which they are declared in the application.xml deployment descriptor.

How is security handled in the WebLogic J2EE Connector Architecture?

Due to the fact that the current configuration and packaging requirements for resource adapters in WebLogic Server require the hand-editing of the weblogic-ra.xml file, any new passwords specified in the security-principal-map entries are done in clear-text. BEA understands the importance of protecting security passwords. Hence, we provide a Converter Tool that allows for the encryption of all passwords present in the weblogic-ra.xml file. The Converter Tool is shipped in the standard weblogic.jar file.

Why am I getting an "ORA-01000: maximum open cursors exceeded" error, even though I closed all ResultSet, Statement, and Connection objects?

This is an Oracle issue. According to Oracle's documentation, dynamic cursors can remain open from run to run in a session and are not closeable when a procedure closes. To work around this issue, you can increase the number of open cursors allowed in the database or you can reset the connection pool (close and reopen database connections in the connection pool).
To reset the connection pool, you can untarget and retarget the connection pool using the Administration Console. You can also use the reset() method through the JMX API or the RESET_POOL command on the WebLogic Server command line interface.

Can I enable requests to a JDBC connection pool for a database connection to wait until a connection is available?

No, there's no way to allow a request to wait for a pool connection, and from the system point of view there should not be. Each requests that waits for a connection ties up one of the fixed number of execute threads in the server, which could otherwise be running another server task. Too many waiting requests could tie up all of the execute threads and freeze the server.

How do I use multibyte character sets with WebLogic jDriver for Informix?

Currently, multibyte character sets are not supported for the WebLogic jDriver for Informix driver.

Why do I get an exception when trying to find a connection factory?

The exception is usually something like java.io.InvalidClassException or java.lang.NoClassDefFoundError.
Make sure weblogic.jar is in the CLASSPATH of the client. Also make sure you have the correct Java run-time jar files included (i.e., you might need rt.jar).

What can I do when I get java.lang.OutOfMemoryError because producers are faster than consumers?

Quotas can be used to help this situation. Your sender will then receive ResourceAllocationExceptions and the server will stay up. WLS 6.X does not support paging of messages out of memory.
As of WLS 6.1 SP02 or later, you can use the Message Paging feature, which can free up valuable virtual memory during peak message load periods by swapping out messages from virtual memory to persistent storage when message loads reach a specified threshold.

Which XML parser comes with WebLogic Server ?

We bundle a parser, based on Apache's Xerces 1.3.1 parser, in WebLogic Server. In addition, we include a WebLogic proprietary high-performance non-validating parser that you can use for small to medium sized XML documents. The WebLogic XML Registry allows you to configure the parser you want to use for specific document types.

How do I turn the auto-deployment feature off?

The auto-deployment feature checks the applications folder every three seconds to determine whether there are any new applications or any changes to existing applications and then dynamically deploys these changes.

The auto-deployment feature is enabled for servers that run in development mode. To disable auto-deployment feature, use one of the following methods to place servers in production mode:

* In the Administration Console, click the name of the domain in the left pane, then select the Production Mode checkbox in the right pane.
* At the command line, include the following argument when starting the domain's Administration Server:

-Dweblogic.ProductionModeEnabled=true

Production mode is set for all WebLogic Server instances in a given domain.

Can I set the deployment order for application modules? For standalone modules?

The Load Order attribute controls the deployment order of standalone modules and applications relative to other modules and applications of the same type. For example, standalone EJBs with smaller Load Order values are deployed before those with higher values.

Modules that are deployed as part of an Enterprise Application (EAR file or directory) are deployed in the order in which they are specified in the application.xml deployment descriptor.

What is the difference between the WL_HOME/config/examples/applications folder and the WL_HOME/config/examples/stage folder?

The applications folder is intended for applications that are not yet ready for a production environment. WebLogic Server dynamically deploys the contents of the applications folder. The stage folder (or a folder that you create for the same purpose) is for storing copies of deployment files that are ready for deployment in a production environment (deployments that use the stage or external_stage deployment modes).

How can I set deployment order for applications?

WebLogic Server allows you to select the load order for applications. WebLogic Server deploys server-level resources (first JDBC and then JMS) before deploying applications. Applications are deployed in this order: connectors, then EJBs, then Web Applications. If the application is an EAR, the individual components are loaded in the order in which they are declared in the application.xml deployment descriptor.

Can I refresh static components of a deployed application without having to redeploy the entire application?

Yes. You can use weblogic.Deployer to specify a component and target a server, using the following syntax:
java weblogic.Deployer -adminurl http://admin:7001 -name appname -targets server1,server2 -deploy jsps/*.jsp

When should I use the -nostage option?

Set the staging mode to -nostage (using weblogic.Deployer or the Administration Console) if you don't want to copy deployment files but want to deploy an application from its present location. All target servers must be able to access the same set of deployment files.

When should I use the external_stage option?

Set -external_stage using weblogic.Deployer if you want to stage the application yourself, and prefer to copy it to its target by your own means.

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Weblogic Interview Questions &FAQ's -1

Weblogic Application Server FAQ's -1

How do I provide user credentials for starting a server?

While creating a domain, the Configuration Wizard prompts you to provide the username and password for an initial administrative user. If you create the domain in development mode, the wizard saves the username and encrypted password in a boot identity file. A WebLogic Server instance can refer to a boot identity file during its startup process. If a server instance does not find such a file, it prompts you to enter credentials. If you create a domain in production mode, or if you want to change user credentials in an existing boot identity file, you can create a new boot identity file.

Can I start a Managed Server if the Administration Server is unavailable?

By default, if a Managed Server is unable to connect to the specified Administration Server during startup, it can retrieve its configuration by reading a configuration file and other files directly. You cannot change the server's configuration until the Administration Server is available. A Managed Server that starts in this way is running in Managed Server Independence mode.

What is the function of T3 in WebLogic Server?

T3 provides a framework for WebLogic Server messages that support for enhancements. These enhancements include abbreviations and features, such as object replacement, that work in the context of WebLogic Server clusters and HTTP and other product tunneling. T3 predates Java Object Serialization and RMI, while closely tracking and leveraging these specifications. T3 is a superset of Java Object. Serialization or RMI; anything you can do in Java Object Serialization and RMI can be done over T3. T3 is mandated between WebLogic Servers and between programmatic clients and a WebLogic Server cluster. HTTP and IIOP are optional protocols that can be used to communicate between other processes and WebLogic Server. It depends on what you want to do. For example, when you want to communicate between a browser and WebLogic Server-use HTTP, or an ORB and WebLogic Server-IIOP.

How do you set the classpath?

WebLogic Server installs the following script that you can use to set the classpath that a server requires:
WL_HOME/server/bin/setWLSEnv.cmd (on Windows)
WL_HOME/server/bin/setWLSEnv.sh (on UNIX)

How do stubs work in a WebLogic Server cluster?

Clients that connect to a WebLogic Server cluster and look up a clustered object obtain a replica-aware stub for the object. This stub contains the list of available server instances that host implementations of the object. The stub also contains the load balancing logic for distributing the load among its host servers.

What happens when a failure occurs and the stub cannot connect to a WebLogic Server instance?

When the failure occurs, the stub removes the failed server instance from its list. If there are no servers left in its list, the stubb uses DNS again to find a running server and obtain a current list of running instances. Also, the stub periodically refreshes its list of available server instances in the cluster; this allows the stub to take advantage of new servers as they are added to the cluster.

How do I limit the number of Oracle database connections generated by WebLogic Server?

You can use connection pools to limit the number of Oracle database connections generated by WebLogic Server in response to client requests. Connection pools allow T3 applications to share a fixed number of database connections.

How does a server know when another server is unavailable?

WebLogic Server uses two mechanisms to determine if a given server instance is unavailable. Each WebLogic Server instance in a cluster uses multicast to broadcast regular "heartbeat" messages that advertise its availability. By monitoring heartbeat messages, server instances in a cluster determine when a server instance has failed. The other server instances will drop a server instance from the cluster, if they do not receive three consecutive heartbeats from that server instance

WebLogic Server also monitors socket errors to determine the availability of a server instance. For example, if server instance A has an open socket to server instance B, and the socket unexpectedly closes, server A assumes that server B is offline.

How are notifications made when a server is added to a cluster?

The WebLogic Server cluster broadcasts the availability of a new server instance each time a new instance joins the cluster. Cluster-aware stubs also periodically update their list of available server instances.

How do clients handle DNS requests to failed servers?

If a server fails and DNS continues to send requests to the unavailable machine, this can waste bandwidth. For a Java client application, this problem occurs only during startup. WebLogic Server caches the DNS entries and removes the unavailable ones, to prevent the client from accessing a failed server twice.

Failed servers can be more of a problem for browser-based clients, because they always use DNS. To avoid unnecessary DNS requests with browser-based clients, use a third-party load-balancer such as Resonate, BigIP, Alteon, and LocalDirector. These products mask multiple DNS addresses as a single address. They also provide more sophisticated load-balancing options than round-robin, and they keep track of failed servers to avoid routing unnecessary requests.

Why do I get an error while trying to retrieve the text for ORA-12705?

This error occurs when you have not set the ORACLE_home environment variable properly — a common mistake. In order to use WebLogic jDriver for Oracle, the Oracle client software needs to be installed and ORACLE_home must be set.
You may also see this error message if you try to use WebLogic jDriver for Oracle's internationalization capabilities with a language/codeset combination that is not installed on your system. If you get the ORA-12705 error with the correct error text, then either you have set NLS_LANG improperly, or you do not have the right codesets installed on your system.

What is Cause for error "ORA-6502?"

The default length of a string bound to an OUTPUT parameter of a CallableStatement is 128 characters. If the value you assign to the bound parameter exceeds that length, you will get this error.
You can adjust the length of the value of the bound parameter by passing an explicit length with the scale argument to the CallableStatement.registerOutputParameter() method.

How can I control on which WebLogic Server(s) my application will run?

A system administrator can specify on which WebLogic Server(s) applications will run by specifying targets when configuring connection factories. Each connection factory can be deployed on multiple WebLogic servers.

Why do I run out of resources during updates with Oracle's database link?

When you use Oracle's database link to update your database, you may get error "maximum number of temporary table locks exceeded" even if you close your result sets and statements when you finish.
The database link is an object in the local database that allows you to access tables, views, and such in a remote database. The database link is controlled by the Oracle server, so the driver has no control over its use of resources. The link appears to perform the commit (since other processes could see the records that were being created), but it doesn't free any resources until the connection is closed. The solution is to remove the database link and use the JDBC driver to do your selects, inserts, and updates.


How can I run multiple instances of the same servlet class in the same WebLogic Server instance?

If you want to run multiple instances, your servlet will have to implement the SingleThreadModel interface. An instance of a class that implements the SingleThreadModel interface is guaranteed not to be invoked by multiple threads simultaneously. Multiple instances of a SingleThreadModel interface are used to service simultaneous requests, each running in a single thread.

When designing your servlet, consider how you use shared resources outside of the servlet class such as file and database access. Because there are multiple instances of servlets that are identical, and may use exactly the same resources, there are still synchronization and sharing issues that must be resolved, even if you do implement the SingleThreadModel interface.


How do I restrict access to servlets and JSPs?

The Java Servlet API Specification v2.2 allows you to declaratively restrict access to specific Servlets and JSPs using the Web Application Deployment descriptor. Section 13.3.2 of the specification has an example deployment descriptor that uses declarative security. For more information, see Programming WebLogic HTTP Servlets.

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Sams - BEA WebLogic Server 8.1 Unleashed

Sams - BEA WebLogic Server 8.1 eBook:

BEA positioned WebLogic Server as the premier J2EE Web Services development platform With the release of WebLogic Server 7.0 in June 2002. WLS integrated WebLogic Workshop and other key tools to provide developers with a stable, market-leading product designed for the next generation of Java applications based on Web Services on the latest J2EE platform With the next release in late 2002.

BEA WebLogic Server is the leading J2EE application server, holding almost 40% of the market share in this competitive category. WebLogic Server Unleashed is designed to be the definitive reference work for the WLS developer, offering an in-depth look at the capabilities provided by WLS 7.X and illustrating the best development practices.

Download BEA WebLogic Server 8.1 eBook

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