.class and .jar

Hi every one,
In a research lab that i'm working, we're developing a big software. Eventually we are trying to make it destributed.
Our problem is that every time we try to send our updated code to the our clients, we send the library in .jar. Bad thing about .jar is that it can be opened and all .class files can be retrieved which let people see the actual code.
Is there any solution to not let the poeple see the actuall source code???
thanx.

Class files do contain actual bytecode, not just "headers". You can use a decompiler to get a reasonable facsimile to the original Java source code, especially if the Java source was compiled with debugging information.
In order to make decompilation harder, you can use an obfuscator to mangle some of the names the program uses. To make decompilation impossible, you can encrypt the class files using strong encryption and write a custom classloader that will decrypt the class files.

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Ameem Sami

Did you find a solution for this? I'm having the same problem.
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Hi Raj,
The Java build path of a DC-project is based on the definitions in de DC-dependecies (shown in .dcdef file).
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Applets and classes and jars

ok, this has probably been asked and answered a million times, but I cannot find it anywhere.
heres my problem:
I have an applet and am trying to run it from internet explorer and all I get is a blank screen. the code is:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" CONFILTERED="text/html; charset=windows-1252"></meta>
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<link type="text/css" rel="stylesheet" href="department.css"/>
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<body></body>
</html>
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and the jar is in
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Nothing to do with Servlets here... but:
The Applet JAR has to be in a path relative to the web page, or the server root. You are asking the client (the web browser the user is using) to download the JAR and look inside for the class to run. So the web browser must be able to see that JAR. As such it needs to be in a directory your server hosts. The easiest is to have it in a directory relative to the page that displays it, such as:
Web Hosted Directory:   C:\Web\HostedDir\
Web page location                       \MyApp\SODAppletPage.html
JAR file location                       \MyApp\lib\SODApplet.jar
Applet tag
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            archive="lib/SODApplet.jar"
            Height=300 Width=300>
    </applet>

Compressing classes and jars using pack200

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I want to compress my j2re1.4.2 based application jars.
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regards,
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http://forum.java.sun.com/index.jsp

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Hi,
The work around I am using to overcome this problem is Unzipping th ear/war file created by servicegen task and including all the classes. Then creating the ear file again by creating a new ant target.
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How to run .class file and .jar file in jdev9i

I want to run .class file and .jar file in jdev9i,what should I do?
Also,I want to generate .class file and .jar file in jdev9i,what should i do?

Add the .class file containing the public static void main(...) method to the project by clicking on the + toolbar button in the navigator, open the project properties and properly set the additional classpath then right click on the .class in the navigator and say run. It should work, I've just tried it.
Doesn't work for a .jar yet, in JDeveloper 9.0.3 it works both for .class and .jar
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Load Jar and access a class in jar at run time

I need help from you.
How to load a Jar and access a class in the jar at run time?
When i try the following code it works fine while running in Java (Jdk1.5).If iam running the same code in servlet,ClassCastException occurs.
Error Message : ClassCastExcption : jartest1 cannot be cast to Thing
test.jar contains jartest.class and Thing.class
jartest1.java
try{
File file =new File("test.jar");
String lcStr ="jartest";
URL jfile = new URL("jar", "", "file:" + file.getAbsolutePath() +"!/");
URLClassLoader cl = URLClassLoader.newInstance(new URL[] { jfile });
Class loadedClass = cl.loadClass(lcStr);
Thing t=(Thing)loadedClass.newInstance();
t.execute();
catch(Exception e)
System.err.println(e);
Thing.java
public interface Thing
void execute();
jartest.java
public class jartest implements Thing
public void exceute()
System.out.println("Welcome");
Thanks and Regards
V.Senthil Kumar
Edited by: senthilv_sun on Dec 16, 2008 8:30 PM

senthilv_sun wrote:
I need help from you.
How to load a Jar and access a class in the jar at run time?
When i try the following code it works fine while running in Java (Jdk1.5).If iam running the same code in servlet,ClassCastException occurs.
Error Message : ClassCastExcption : jartest1 cannot be cast to ThingPresumably we can only hope that that is a transciption error. It always helps to use copy and past actual errors and code rather than manually typing them.
test.jar contains jartest.class and Thing.classWrong.
The interface class and plugable class must not be in the same jar.
A plugable interface requires two components
- Interface (generic sense)
- Functional components.
The Interface must be independant (own jar) so that it is available to the framework (user of plugin) and to the functional components. And the plugable component must not be on the java class path.
This also means that we know for certain that the plugable component is also on the system class path. That is a bad idea as well.
Given that it is pretty pointless to even speculate as to why this error is showing up. Create the correct jar layout. Test using the command line. Then test using servlets. Insure that the plugable jar is NOT on the java classpath for both tests.

Java classes in Jar and Cab files

Hello all,
Our product supply java classes in Jar and Cab files that the browser downloads each time.
The files are big and it takes a long time.
Do you know of a way to make the cab/jar files be copied in to the user computer and that the browser would know to download files again only if there is a new version (otherwise take it from the local computer)
Please help me
Tamg

I think I've seen an option for this with manifest files (or was it something that had to do with the java plug-in). There was something about the version and only download a new version if it was newer than the one on your local computer. This version thing is something you define in the manifest file at least. Take a look at jar and manifest files, there might be something there.

How to modify a class in .jar and compile it back

Hi,
I have questions reg .jar, I need to test my application and I need to modify certain files in that .jar and compile it back. How do I do that? I have extract all the classes and decompile it to .java, and I just want to edit just 1 file, but I always have problems compiling it. Am i doing it the wrong way?Please help...
Thanks.

Did you make a jar and now need to make changes? Help me to understand why you decomplied the class files? Can you not just make a new jar?

Applets and classes in jar files

I have placed an applet and a group of classes that the applet uses in a jar file.
The classes are grouped in their own files in a short directory tree within the jar file.
When the applet is loaded by the browser on a client with the usual CODE="appletname.class" and ACRCHIVE="jarname.jar" statements, are the related class files and the directory tree also loaded into the client? Or do they remain at the server to be used by the applet as necessary?

I'd say the entire JAR will be downloaded.

How to modify a specific class in jar file ?

I've downloaded a jar file for applet, the jar file works fine... but when I extract a specific class file from the jar file and just recompie it from my IDE (Eclipse) without even making any change and then compress again jar class files including the new modified class file instead of the old one (without any modifications to other classes)... then I get
(NoSuchMethodError ) exception whenever methods of other classes are invoked from within the modified class !!
...The manifist file of the jar file reads the following line
Created-By: 1.4.0_01 (Sun Microsystems Inc.)
I thought it means that jar class files were built using JDK 1.4.0_01 ...I used JDK 1.5.0_01 in my IDE...
I thought JRE incompatiblity was the reason of the problem so I downloaded JRE 1.4.0_01 and used it to build this class file... but i got the same exception..
so what is the main reason of the problem ? ...should I make changes to IDX files accompanying applet jar files ??
If no, then how can I overcome this problem and be able to change and rebuild a specific class from this jar file ?
(I cannot rebuild all classes in jar because there are errors I cannot resolve !!)

Could you please clarify: do you want to run your project or a project from an independent jar?
In the first case just select Run Project from the project context menu or select a class with main method and click Run File in the class context menu.
Regarding the second case:
- I don't think there is such a feature in the IDE (running third party jars is not an IDE function). Could you explain why you need this?

How to pack .class or .jar with jvm into an exe file?

In fact, .class or .jar files are middle layer files who need JVM to explain and run them. Sometimes it's unconvenient. Why not provide some tools to pack .class or .jar with jvm into exe file?

because java should be able to run on any OS. That is why SUN doesn't provide such tool. There are other company's who does provide such tool. Like JBuilder enterprise

How to convert .class into .jar file

Hi,
How to convert .class into .jar file

jsf_VWP5.5.1 wrote:
Hi,
How to convert .class into .jar fileFrom a command prompt, cd to the location of your .class file(s).
If you want to create a simple jar, use: jar -cf Whatever.jar Whatever.class
If you want to compile all .class files in a directory into a jar, use *.class instead.
Now, I'm going to assume you want to create an executable jar... here's how to do that:
1) Create a blank text file; for this example, lets call it main.txt.
2) In the first line of main.txt, type: Main-class: Whatever ('Whatever' should be the name of the class in your program where the main() method is located)
3) Press enter to go to the next line (someone please correct me if I'm wrong, but if you don't insert the line break/CR after the Main-class: statement, this will not work... in my experience, this is true)
4) Make sure you save this file in the same directory as your .class file(s).
5) Type: jar -cmf Whatever.jar main.txt Whatever.class
...and that's about it. For more information on the usage of the jar command and to understand the switches (such as -cmf), try jar --help.
Hope that helps.

.class and .jar

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