Load a class from strea

Hi i have a strange problem:i save a class object in a database blob then i want to read the object and set them in to the class path.Is possible?

i save a class object in a database blob then i want to read the object Do you save a Class or an instance of that Class?
set them in to the class path.Is possible?If you want to save a Class and load it, you need a custom ClassLoader which can read the blob and call defineClass with the bytes.
If you want to save an Object and load it, you need to read the bytes and then use an ObjectInputStream to read the object. The Class must be on the system classpath or you need to subclass ObjectInputStream and (I think) override resolveClass.

Similar Messages

Problem in loading a class from server

hello,
Please help me ,i m using this code to load a class from server and this code load this successfully but i don't how to make object of class that is just loaded.
i want to load the class and use its method in my program please help me i m in very critical position.
pelase help me give me hint
import java.sql.*;
import java.net.*;
import java.io.*;
public class MyLoader
public static void main (String argv[]) throws Exception
URLClassLoader loader = new URLClassLoader(new URL[] { new URL("url") });
// Load class from class loader. argv[0] is the name of the class to be loaded
String str = "FinalMyConnection";
     Class c = loader.loadClass (str);
System.out.println(c.getClass().getName());
// Create an instance of the class just loaded
Object o = c.newInstance();
     System.out.println(o.getClass());
     FinalMyConnection mycon = new FinalMyConnection();
     String query1 = " select * from game_master order by game_id;";
     mycon.connect();
          ResultSet rs1=mycon.executequery(query1);
          while (rs1.next())
          String s1=rs1.getString(1);
               String s2=rs1.getString(2);
               System.out.println("game_id"+s1);
               System.out.println("game_name"+s2);
}

also load all required parser and sax classes into oracle,i.e.,
you can load the '.jar' file containg all the parser and sax classes and then load you ContentHandler class.

Can't load any classes from infobus.jar (WL 6.0 SP1)

Hi,
I am deploying an .ear file, which has one .war file in it. The war file, has
infobus.jar, inside it under \WEB-INF\lib. Whenever in my servlet code I try to
load a class from infobus.jar, I get the following exception :
About to load class javax.infobus.InfoBusDataConsumer<<<<<<<<<<java.lang.ClassNotFoundException: InfoBusDataConsumer
at weblogic.utils.classloaders.GenericClassLoader.findClass(GenericClassLoader.java:178)
at weblogic.utils.classloaders.ChangeAwareClassLoader.findClass(ChangeAwareClassLoader.java:45)
at java.lang.ClassLoader.loadClass(ClassLoader.java:297)
at java.lang.ClassLoader.loadClass(ClassLoader.java:253)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:313)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:120)
at XDILoginForm.init(XDILoginForm.java:99)
at weblogic.servlet.internal.ServletStubImpl.createServlet(ServletStubImpl.java:638)
at weblogic.servlet.internal.ServletStubImpl.createInstances(ServletStubImpl.java:581)
at weblogic.servlet.internal.ServletStubImpl.prepareServlet(ServletStubImpl.java:526)
at weblogic.servlet.internal.WebAppServletContext.preloadServlet(WebAppServletContext.java:1078)
at weblogic.servlet.internal.WebAppServletContext.preloadServlets(WebAppServletContext.java:1022)
at weblogic.servlet.internal.HttpServer.loadWARContext(HttpServer.java:499)
at weblogic.servlet.internal.HttpServer.loadWebApp(HttpServer.java:421)
at weblogic.j2ee.WebAppComponent.deploy(WebAppComponent.java:74)
at weblogic.j2ee.Application.deploy(Application.java:175)
at weblogic.j2ee.J2EEService.deployApplication(J2EEService.java:173)
at weblogic.management.mbeans.custom.Application.setLocalDeployed(Application.java:217)
at weblogic.management.mbeans.custom.Application.setDeployed(Application.java:187)
at java.lang.reflect.Method.invoke(Native Method)
at weblogic.management.internal.DynamicMBeanImpl.invokeSetter(DynamicMBeanImpl.java:1136)
at weblogic.management.internal.DynamicMBeanImpl.setAttribute(DynamicMBeanImpl.java:773)
at weblogic.management.internal.DynamicMBeanImpl.setAttribute(DynamicMBeanImpl.java:750)
at weblogic.management.internal.ConfigurationMBeanImpl.setAttribute(ConfigurationMBeanImpl.java:256)
at com.sun.management.jmx.MBeanServerImpl.setAttribute(MBeanServerImpl.java:1356)
at com.sun.management.jmx.MBeanServerImpl.setAttribute(MBeanServerImpl.java:1331)
at weblogic.management.internal.ConfigurationMBeanImpl.updateConfigMBeans(ConfigurationMBeanImpl.java:318)
at weblogic.management.internal.ConfigurationMBeanImpl.setAttribute(ConfigurationMBeanImpl.java:259)
at com.sun.management.jmx.MBeanServerImpl.setAttribute(MBeanServerImpl.java:1356)
at com.sun.management.jmx.MBeanServerImpl.setAttribute(MBeanServerImpl.java:1331)
at weblogic.management.internal.MBeanProxy.setAttribute(MBeanProxy.java:291)
at weblogic.management.internal.MBeanProxy.invoke(MBeanProxy.java:173)
at $Proxy7.setDeployed(Unknown Source)
at weblogic.management.console.pages._panels._mbean._application._jspService(_application.java:303)
at weblogic.servlet.jsp.JspBase.service(JspBase.java:27)
at weblogic.servlet.internal.ServletStubImpl.invokeServlet(ServletStubImpl.java:213)
at weblogic.servlet.internal.WebAppServletContext.invokeServlet(WebAppServletContext.java:1265)
at weblogic.servlet.internal.ServletRequestImpl.execute(ServletRequestImpl.java:1622)
at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:137)
at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:120)
But if I put the infobus.jar on system classpath , everything works out fine.
Can somebody tell me, what is going on

Gseel is right: you try to instantiate an EJB with the BDK.
Enterprise Java Beans are totally different from graphical/GUI beans. EJBs are thought for dealing with business logic like accessing a database, ldap directory and so on. They run on a application server (simply speaking - a java enabled webserver) and do some processing to handle user requests. Enterprise Java Beans usually don't interact directly with the user, they only do the work in the background and forward their results, which are then rendered for the user. Typically they are employed for handling web requests (a user with a browser), but they can also be used for awt/swing applications. Though - let me repeat - they don't appear visually on the screen.
The only similarities between those two bean types are the following: they have getter/setter methods for their properties, they implement Serializeable (or a sub-interface like Externalizable, Remote) and they have a default no-argument constructor.
If you want to run your been you need an application server (your bean is pre-packaged for the Bea Weblogic app-server). If you want to do something graphical, you'll need to search for GUI beans.
dani3l

How to load java class from jsp page?

hi all!
Does anyone know how to load java class from jsp page?
I try to load java class from jsp page.
Is it possible to load java class fom jsp page?
thanks and have a good day!

What I mean is How to load/open java class file from jsp page?
I think we can open Applet from jsp page by using
<applet code=helloApplet.class width=100 height=100>
</applet>
but, how to open java class which is an application made by Frame?
thanks and have a good day

Problem loading modified classes from CLASSPATH using system class loader

Hi,
I am facing problem to load the modified classes from CLASSPATH.
I have set my CLASSPATH to a directory whose classes will be modified frequently. After the server(web/app) is started, the system class loader, using which am trying to load the classes from the directory where the CLASSPATH is set, am not able to load the modified files without the server restart.
Do I need to have a custom class loader to fix this.
Please help me.
Thanks,
Sureddy

Do I need to have a custom class loader to fix this.Yes.

Is there a restriction on loading "javax" classes from WEB-INF/lib?

I'm having trouble with a webapp in WL 10MP1 that is having trouble loading classes from the "jsr311-api-1.0.jar" in my WEB-INF/lib. Even though I have no trouble with it in Eclipse (no compile errors), classes from that jar fail with "NoClassDefFound" exceptions. I have a feeling it might be the fact that the packages in that jar start with "javax". Assuming that's the case, is there anything I can do to fix this?
What's even stranger is that the errors I get are when I try to load them directly from the Spring context. However, if I remove the test references to those classes, there's other code that loads those classes later in the application startup (after the Spring context finishes loading), and they load perfectly fine (I turned on verbose class loading to verify this).

Note that I've tried two other strategies that both result in the same failed state.
I tried putting the "jsr311-api-1.0.jar" in $JDK_HOME/jre/lib/ext, but that causes a failure to find Spring classes. I then copied the "spring.jar" into $DOMAIN_HOME/lib, and then it fails to find CXF classes. After doing the same with "cxf-2.2.3.jar", it then fails to find "javax.servlet.ServletContextListener", which clearly tells me there's no benefit to this approach.
Similarly, I tried copying the jars into $DOMAIN_HOME/lib, and that fails to find "org.apache.commons.logging.LogFactory". I could continue down this path, but it doesn't seem likely to succeed. Eventually, I'll get to a point where it just can't find the classes specific to my application, which I certainly can't copy into $DOMAIN_HOME/lib.
The first basic problem is that I can't put anything into a higher-level classloader that will eventually reference classes in a lower-level classloader, because references can only go up the chain, and the second problem is that WebLogic appears to ignore classes in WEB-INF/lib in the "javax.*" packages. I think there might be an exception for "javax.xml.*", but not for other subpackages. I tried adding a "prefer-application-packages" clause to my weblogic-application.xml file, but that had no effect.

How to load a class from its name.

Hi,
In my program, I want users can write their own classes, these classes need to implement an interface and name of class will be stored in database. I use Class.forName() to load these classes but I cannot type-cast to interface. Please help me.
Here is the code in my program:
public interface A {
public void doSomething();
public class test {
public static void main(String[] args) {
A clazz = (A)Class.forName("MyClass"); // error here
A.doSomething();
}

Hai,
Refine your test class as follows:
public class test
public static void main(String arg[])
try
Class clazz = Class.forName("MyClass");
Object obj = clazz.newInstance();
((MyClass)obj).doSomething();
catch(Exception ex)
System.out.println(ex);
Regards
Raja.

Unable to load Java classes from byte arrays.

I have an application started through JWS. It works fine except for one problem. The application allows the user to load an external class, typically received over a socket. These are not (and cannot) be signed. My application complains about not being able to load these when starting through JWS. When starting the application locally (i.e., run the jar file using 'java -jar APP.jar') it works fine.
I guess I have to grant som additional permissions in my policy-file. But since these classes are user-defined, there is no way for me to define a static codebase. `
Any ideas?

Java Web Start installs a SecurityManager, and after that is responsible for assigning permission collections to any code loaded by the JNLPCLassLoader.
If you have all-permissions for your jnlp loaded code, then use another ClassLoader to load some other code, That other class loader will assign the permissions to that code. If that ClassLoader dosn't extend SecureClassLoader, the code will get only the default permissions.
You can fix this by
1.) Use a ClassLoader that extends SecureClassLoader, and override getPermissions(), or
2.) just call System.setSecurityManager(null), from the trusted code loaded by the JNLPCLassLoader.
/Dietz

How to load a class from a jar not in the classpath

I have a gazillion jars of class files that I want to access dynamically in an application. I don't want to list every jar. The jars also contain images. With images you can explicitly point to the jar with and load the image with createImage....
"jar:file:/C:/myjarlocation/myjar.jar!/pathtoimage/image.gif"
Is there a similar string you can use when creating classes on the fly in a classloader with getClass().forName("classname") ??

Hm, if you are not in an EJB container or some other environment that won't let you create a classloader, you might create a new URLClassLoader with a path pointing to those JARs. You will probably want to use your normal application class loader as the parent loader, so any referenced common class definitions are found during the load.
Note that - in order to make use of the classes - you will normally need to know that they implement some interface (or inherit from a common base class) to which you can cast their instances. These Interfaces/base classes will have to be packaged for normal loading by your application class loader; else the cast will trigger an error during compile time. After this, loading them dynamically during runtime is no longer an option since they are referenced directly in the sourcecode.
Alternatively you might do away with interfaces/base classes and call methods of dynamically loaded classes also dynamically: via reflection. But I guess this is too cumbersome for what you might have in mind. Also it has more invocation overhead, less type safety and handling all these exceptions wrapped in InvocationTargetExceptions can quickly become a nightmare too...

Loading a class from specified classpath

Hello,
I would like to create an instance of a class in a specific directory.
So, I am doing this way :
System.setProperty("java.class.path", classPath.getAbsolutePath());
Class object = Class.forName(name);
Object instance = object.newInstance();It works perfectly when running in my IDE (Eclipse).
But when I am running my application through a JAR, I encountered the following error :
ClassNotfoundException
I don't understand why an exception is thrown whereas I defined correctly my classpath.
Could you help me ?

When running from an executable jar the normal class path is ignore in favour of thejar and any Class-Path specified in the jar's manifest.
What you want is a URLClassLoader. Bascially:
URLClassLoader cl = new URLClassLoader(new URL[]{classPath.toURL()});
Class clazz = cl.loadClass(fullName);(Catch assorted exceptions)
There should not be a class of the given name in the jar, or libraries it references (if there is, that will be loaded in preference).

Load java class from another directory

Hi. I am new to Java. I am trying to load a java object from a subdirectory. Is that possible? Thanks in advance!

Thanks for the quick reply!
I tried this:
set CLASSPATH =
Data;Application;Entertainment;MiniGames;
but it doesn't seem to work...
The actual subdirectory is
\Data\Application\Entertainment\MiniGames
I am new to Java, so please bear with me with my
stupidity... please advice again.
Thanks in advanceClasspath needs to contain the actual directory paths, not a relative path. So it should be something like .;c:\Data\Application\Entertainment\MiniGames

Itunes-error "Itunes was unable to load data class information from sync services"

Something is going wrong when ever i want to plug in my ipod-using itunes. It loads for like 5 minutes then a error message pops up saying "Itunes was unable to load data class from sync services. reconnect or try again later."
Though it works when i restart the computer but i dont want to have to restart the computer everytime i want to sync my ipod to itunes.
I have uninstalled itunes too and downloaded it again and still keeps doing this.

OK. Try this article:
iTunes for Windows: "Unable to load data class" or "Unable to load provider data" sync services alert
http://support.apple.com/kb/TS2690

Failover to loading classes from codebase?

The Java Plug-In fails over to loading class files from codebase when the jars specified do not contain the class in question.
I need this same behavior from Java Web Start -- in part because I'd like to convert some applets and in part because due to customization, reflection, etc, it is not possible for me to force all class files to reside in the jars. Some will only be found in the codebase.
Is there any way to accomplish this with Java Web Start? Or do we have to use another JNLP implementation? I understand performance is best when the jars are complete, but why did Sun make Java Web Start's behavior so inconsistent. [This is not the only case of this, but I'll keep my other questions/gripes on this matter to other threads.]

I fully agree with your opinions on the environment variables such as CLASSPATH, PATH etc.
But my problem is: I want to force the application to load the classes over RMI from the codebase specified by the other machine first before trying to load the classes from its own class path specified by -cp or whatever mechanisms.
In other words, I want to load the classes remotely instead of locally on the hard drive if the classes with the same names exist locally.

Is it possible to load classes from a jar file

Using ClassLoader is it possible to load the classes from a jar file?

URL[] u = new URL[1] ;
u[0] = new URL( "file://" + jarLocation + jarFileName + "/" );
URLClassLoader jLoader = new URLClassLoader( u );
Object clsName = jLoader.loadClass( clsList.elementAt(i).toString() ).newInstance();
I get this error message.
java.lang.ClassNotFoundException: ExceptionTestCase
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:297)
at java.lang.ClassLoader.loadClass(ClassLoader.java:253)
// "file://" + fileLocation + fileName + "/" This works fine from a browser.
Is there anything I am missing? Thanks for the reply.

Loading classes from another jar file

I've set up my jnpl file so that it references a core jar file (contains main() function). The jnlp also references another jar file (app.jar) which contains class files that I load and instantiate dynamically (using ClassLoader). The core.jar file contains a manifest that includes a reference to app.jar.
The app works fine when I use "java -jar core.jar" from the command line.
However, when I wrap the jars using jnlp, I always get a null pointer exception because it cannot find any class that is in the app.jar file. I've tried different strategies, such as trying to load a class file that sits on the server (in a jar file and not in a jar file), but that also fails if I use jnlp (However, it works if I use "java -jar core.jar")
Any ideas what is going on?

This is the "OckCore.jar" manifest before signing:
Manifest-Version: 1.0
Main-Class: com.Ock.OckCore.OckApp
Class-Path: . OckMaths.jar
Created-By: 1.4.0-beta3 (Sun Microsystems Inc.)
Name: com.Ock.OckCore.OckApp.class
Java-Bean: FalseThis is the manifest after signing:
Manifest-Version: 1.0
Main-Class: com.Ock.OckCore.OckApp
Created-By: 1.4.0-beta3 (Sun Microsystems Inc.)
Class-Path: http://hazel/Ock/. http://hazel/Ock/OckMaths.jar
Name: com/Ock/OckCore/OckApp.class
SHA1-Digest: KRZmOryizx9o2L61nN+DbUYCgwo=I have removed a load of irrelevant stuff from the "after" manifest to keep it readable.
note that :-
The OckApp.class loads normally from webstart and tries to load a class from OckMaths.jar.
I can prove that OckApp.class does load because it creates a log file when it does.
The OckApp.class tries to load a class from the OckMaths.jar. This fails if webstart is used but works if OckCore is launched using "java -jar OckCore.jar".
The jars do exist at the location specified by the manifest.
The application launches normally if I use "java -Jar OckCore.jar"
Here is the jnlp file
<?xml version='1.0' encoding='UTF-8'?>
<jnlp
     spec="1.0"
     codebase="http://hazel/Ock"
     href="OckMaths.jnlp">
     <information>
          <title>Ock Maths Demo</title>
          <vendor>Rodentware Inc</vendor>
          <description>Demo of a ported app running as a Java Webstart application</description>
          <description kind="short">An app running as a Java Webstart application"></description>
          <offline-allowed/>
     </information>
     <security>
          <all-permissions/>
     </security>
     <resources>
          <j2se version="1.3"/>
          <jar href="OckCore.jar"/>
          <jar href="OckMaths.jar"/>
     </resources>
     <application-desc main-class="com.Ock.OckCore.OckApp">
</jnlp> I have also signed the jars outside of a webdirectory. I get the following manifest file:
Manifest-Version: 1.0
Main-Class: com.Ock.OckCore.OckApp
Created-By: 1.4.0-beta3 (Sun Microsystems Inc.)
Class-Path: . OckMaths.jar
Name: com/Ock/OckCore/OckApp.class
SHA1-Digest: KRZmOryizx9o2L61nN+DbUYCgwo=
note that :-
The jars do exist at the location specified by the manifest.
The application launches normally if I use "java -Jar OckCore.jar".
The application doesn't launch from webstart.
I've found that cache, but the jar files have been renamed.
OckCore.jar is anOckCore.jar, etc... so I'm not sure if trying to write a cmdline will work anyway.

Load a class from strea

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