Saturday, 16 August 2014

CAFEBABE - Print the magic number from Java class file

Isn't it interesting to know that Java class files have a 4 byte header which could be read as CAFEBABE in Hexadecimal. This is being mentioned in Wikipedia: Java class file.

Have you ever tried printing this secret code out? If not, let's do that.

Below is the code which reads it's own class file and prints the code to output stream.

 package com.javavirtues.cafebabe;  
 import java.io.File;  
 import java.io.FileInputStream;  
 import java.io.IOException;  
 public class PrintHeader {  
      public static void main(String[] args) {  
           File classFile = new File(  
                     "bin/com/javavirtues/cafebabe/PrintHeader.class");  
           if (classFile.exists()) {  
                System.out.println("Class file exists. Reading header.");  
                byte[] readHeader = new byte[4];  
                FileInputStream fileInputStream = null;  
                try {  
                     fileInputStream = new FileInputStream(classFile);  
                     fileInputStream.read(readHeader);  
                     for (byte readByte : readHeader) {  
                          System.out.printf("%02X", readByte);  
                     }  
                } catch (IOException exception) {  
                     exception.printStackTrace();  
                } finally {  
                     if (fileInputStream != null) {  
                          try {  
                               fileInputStream.close();  
                          } catch (IOException e) {  
                               e.printStackTrace();  
                          }  
                     }  
                }  
           }  
      }  
 }  

You can download the eclipse project here.

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