Updating .Class File in Jar

Updating .class file in jar

This tutorial details how to update a jar file

jar -uf jar-file <optional_folder_structure>/input-file(s)     

where 'u' means update.

How can I replace a class file in jar files?

In Eclipse i think it should be enough to export your code as jar file.

http://viralpatel.net/blogs/create-jar-file-in-java-eclipse/

So basically you get the old jar, extract, load as project in eclipse and export as jar file.
And you're done.

Replace a single file from jar file

Maybe the jar -uf found here could help you: How to update one file in a zip archive

If graphical apps are an option, you could use winrar or 7-zip to replace the class. You don't need to extract the jar file to make this work. Just open the jar with one of those apps, go to de directory where is the class file to be replaced, drag-and-drop the new file to replace the old one and save.

Updating class in jar, specify directory?

You need to be explicit. It's perfectly valid to have different classes with the same name in different packages. e.g.

com.example.package.A
com.example.package.subpackage.A

etc...

Updating .JAR's contents from code

A Java JAR file is a normal ZIP file. You can therefore open and modify it with code dealing with ZIPs.

Here's a snippet which works (courtesy of David):

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipOutputStream;

public class JarUpdater {
    public static void main(String[] args) {

        File[] contents = {new File("F:\\ResourceTest.txt"),
                           new File("F:\\ResourceTest2.bmp")};

        File jarFile = new File("F:\\RepackMe.jar");

        try {
            updateZipFile(jarFile, contents);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    public static void updateZipFile(File zipFile,
             File[] files) throws IOException {
               // get a temp file
        File tempFile = File.createTempFile(zipFile.getName(), null);
               // delete it, otherwise you cannot rename your existing zip to it.
        tempFile.delete();

        boolean renameOk=zipFile.renameTo(tempFile);
        if (!renameOk)
        {
            throw new RuntimeException("could not rename the file "+zipFile.getAbsolutePath()+" to "+tempFile.getAbsolutePath());
        }
        byte[] buf = new byte[1024];

        ZipInputStream zin = new ZipInputStream(new FileInputStream(tempFile));
        ZipOutputStream out = new ZipOutputStream(new FileOutputStream(zipFile));

        ZipEntry entry = zin.getNextEntry();
        while (entry != null) {
            String name = entry.getName();
            boolean notInFiles = true;
            for (File f : files) {
                if (f.getName().equals(name)) {
                    notInFiles = false;
                    break;
                }
            }
            if (notInFiles) {
                // Add ZIP entry to output stream.
                out.putNextEntry(new ZipEntry(name));
                // Transfer bytes from the ZIP file to the output file
                int len;
                while ((len = zin.read(buf)) > 0) {
                    out.write(buf, 0, len);
                }
            }
            entry = zin.getNextEntry();
        }
        // Close the streams        
        zin.close();
        // Compress the files
        for (int i = 0; i < files.length; i++) {
            InputStream in = new FileInputStream(files[i]);
            // Add ZIP entry to output stream.
            out.putNextEntry(new ZipEntry(files[i].getName()));
            // Transfer bytes from the file to the ZIP file
            int len;
            while ((len = in.read(buf)) > 0) {
                out.write(buf, 0, len);
            }
            // Complete the entry
            out.closeEntry();
            in.close();
        }
        // Complete the ZIP file
        out.close();
        tempFile.delete();
    }
}

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