Java redirect the sysout of a class in a jar

Question

I would like to redirect/hide the sysout generated by the following code :

Tools tool = new ToolsImpl();
HashCode hash = tool.computeHashCodes(dir);

The difficult part is : the method computeHashCodes is stored in a jar.

I've tried the following code :

PrintStream printStreamOriginal=System.out;
System.out.println("sysout deactivated");

System.setOut(new PrintStream(new OutputStream() {
   public void write(int b) {}
}));

System.out.println("Text to delete");

Tools tool = new ToolsImpl();
HashCode hash = tool.computeHashCodes(dir);

System.setOut(printStreamOriginal);
System.out.println("sysout reactivated");

The "text to delete" is indeed deleted, but the sysout generated by the ".computeHashCodes" is not. Does someone know how to hide this sysout ?

Thx in advance, Mike

Answer 1

Thanks everyone, I finally managed to avoid displaying the sysout.

When Magodiez advised me to find how the output was done, I thought I couldn't do that because I didn't have access to the source code ; but then I realised I just had to decompile the code.

So I decompiled it with Java Decompiler, and then I saw how the output was done :

LOGGER.log(Level.INFO, str2);

Then I resolved my problem by using the following line :

java.util.logging.Logger.getLogger("log.tools").setLevel(Level.SEVERE);

It is actually what I really wanted, now only the SEVERE messages will be printed on the sysout.

Thanks again !

Answer 2

The code may be writing to System.err instead.

Try the same exercise but with System.err instead of System.out.

Answer 3

your solution works fine when using System.out, so I'm guessing that the code you want to "block" doesn't use System.out for the output. Try to find how the output is done, so you can "block" it.

Answer 4

See here:

Writing to jars

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.util.jar.JarEntry;
import java.util.jar.JarOutputStream;
import java.util.jar.Manifest;

public class CreateJarFile {
  public static int BUFFER_SIZE = 10240;
  protected void createJarArchive(File archiveFile, File[] tobeJared) {
    try {
      byte buffer[] = new byte[BUFFER_SIZE];
      // Open archive file
      FileOutputStream stream = new FileOutputStream(archiveFile);
      JarOutputStream out = new JarOutputStream(stream, new Manifest());

      for (int i = 0; i < tobeJared.length; i++) {
        if (tobeJared[i] == null || !tobeJared[i].exists()
            || tobeJared[i].isDirectory())
          continue; // Just in case...
        System.out.println("Adding " + tobeJared[i].getName());

        // Add archive entry
        JarEntry jarAdd = new JarEntry(tobeJared[i].getName());
        jarAdd.setTime(tobeJared[i].lastModified());
        out.putNextEntry(jarAdd);

        // Write file to archive
        FileInputStream in = new FileInputStream(tobeJared[i]);
        while (true) {
          int nRead = in.read(buffer, 0, buffer.length);
          if (nRead <= 0)
            break;
          out.write(buffer, 0, nRead);
        }
        in.close();
      }

      out.close();
      stream.close();
      System.out.println("Adding completed OK");
    } catch (Exception ex) {
      ex.printStackTrace();
      System.out.println("Error: " + ex.getMessage());
    }
  }
}