Getting error Incompatible magic value 1784772193 in class file

[sanyam Goel]

Hello everyone,


I have created a custom loader. while reading class files form disk compiler throws an error "Exception in thread "AWT-EventQueue-0" java.lang.ClassFormatError: Incompatible magic value 1784772193 in class file.....

at java.lang.ClassLoader.defineClass1(Native Method)" It also includes the line of code containing the statement "classTemp= defineClass( classFilename, raw, 0, raw.length);" please suggest some solution

Thanks in advance

[Maneesh Godbole]

Welcome to the Ranch.

This message usually indicates that you used a higher java version to compile the code, than the java version you are using to run it.

[Rob Spoor]

I don't think so. The error message for that is different: "unsupported class version". This one does mean that there's something wrong with the class files. Can you show us how you create a byte[] from the class file?

[Maneesh Godbole]

Oops!
Rob is right. As usual I am not thinking straight. Time for me to reboot.

[sanyam Goel]

Rob Spoor wrote:I don't think so. The error message for that is different: "unsupported class version". This one does mean that there's something wrong with the class files. Can you show us how you create a byte[] from the class file?

This is the method I have created to convert a file to a byte array

private byte[] ConvertToBytes(File file) throws IOException{
		
		long lengthOfFile = file.length();
		byte temp[] = new byte[(int)lengthOfFile];
		FileInputStream fin = new FileInputStream(file);
		String str = fin.toString();
		temp=str.getBytes();
		fin.close();
		return temp;
	}

And in another method this array is being converted to a class file.. Here is the code fragment

....
try {
			
			byte raw[] = this.ConvertToBytes(file);
			System.out.println("M here"+ raw.length);
			System.out.println(file.getName());
			 classTemp= defineClass( classFilename, raw, 0, raw.length);      // Here I get the error message 
			 System.out.println(classTemp.getName());
			} catch( IOException ie ) {
		
			}
			if (classTemp==null) {
				classTemp = findSystemClass( file.getName());
				}
			return classTemp;

Please Help!!

[sanyam Goel]

Maneesh Godbole wrote:Welcome to the Ranch.

This message usually indicates that you used a higher java version to compile the code, than the java version you are using to run it.

Yes Maneesh I found this on Internet and I recompiled my classes to be loaded and and again re-ran the program.. but still I encountered the same problem

Here is the complete error I am getting again and again..

Exception in thread "AWT-EventQueue-0" java.lang.ClassFormatError: Incompatible magic value 1784772193 in class file DeckOfCards/class
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(Unknown Source)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.lang.ClassLoader.defineClass(Unknown Source)
at classLoader.ClassLoaderOfExtClass.loadClassCustom(ClassLoaderOfExtClass.java:161)
at guiTool.SeQuenceDiagramGeneration.jMenuItem1ActionPerformed(SeQuenceDiagramGeneration.java:136)
at guiTool.SeQuenceDiagramGeneration.access$0(SeQuenceDiagramGeneration.java:100)
at guiTool.SeQuenceDiagramGeneration$1.actionPerformed(SeQuenceDiagramGeneration.java:70)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.AbstractButton.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Please Help!!

[Darryl Burke]

You're using a String as an intermediary for binary data. That's just plain wrong. And in any case, the tostring() method of FileInputStream is inherited from Object -- what made you think that would return the content of the File?

You need to read the FIle into a byte array and use that to define the class. Also, is the 'classFilename' going to be the same as he expected binary name of the class? Think about it.

[sanyam Goel]

Darryl Burke wrote:You're using a String as an intermediary for binary data. That's just plain wrong. And in any case, the tostring() method of FileInputStream is inherited from Object -- what made you think that would return the content of the File?

You need to read the FIle into a byte array and use that to define the class. Also, is the 'classFilename' going to be the same as he expected binary name of the class? Think about it.

Thank you so much Darryl !! Yes you were right now it is working perfectly fine

[Darryl Burke]

Now that you have it working, you may like to take a look at File Class Loader.

[Rob Spoor]

Darryl, I don't like your way of reading the file. There are two things that can go wrong:

         byte[] bytes = new byte[fis.available()];
         int read = fis.read(bytes);
         if (read != bytes.length) {
            return null;
         }

1) fis.available() doesn't necessarily return the file size. Using (int)file.length() is safer. Only if the file is over 2TB large will that fail, but the entire file couldn't be put into a byte[] anyway.
2) fis.read(bytes) can often read less than the requested number of bytes. I'd instead use a DataInputStream around the FileInputStream and use its readFully method.

[Vipin .Kumar]

hey i have the same problem, where i want to compile java source code and store bytecode directly in an object.
bytecode store in byte[] array but when i use defineClass method from ClassLoader class then "java.lang.ClassFormatError: Extra bytes at the end of class file Main" this error accur.

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<>();
        ByteArrayOutputStream bytecodeOutput = new ByteArrayOutputStream();

        // Create a custom JavaFileManager to collect the bytecode
        JavaFileManager fileManager = new BytecodeFileManager(
                compiler.getStandardFileManager(diagnostics, null, null),
                bytecodeOutput
        );

        // Create a Java source file object
        JavaFileObject fileObject = new JavaSourceFromString("Main", javaCode);

        // Compile the code
        JavaCompiler.CompilationTask task = compiler.getTask(
                null, fileManager, diagnostics, null, null, Collections.singletonList(fileObject)
        );
        if(task.call()){
            return bytecodeOutput.toByteArray();
        }

----------------------------------------------------------------
public class BytecodeFileManager extends ForwardingJavaFileManager<JavaFileManager> {
    private final ByteArrayOutputStream bytecodeOutput;

    public BytecodeFileManager(JavaFileManager fileManager, ByteArrayOutputStream bytecodeOutput) {
        super(fileManager);
        this.bytecodeOutput = bytecodeOutput;
    }

    @Override
    public JavaFileObject getJavaFileForOutput(Location location, String className, JavaFileObject.Kind kind, FileObject sibling) throws IOException {
        if (kind == JavaFileObject.Kind.CLASS) {
            return new SimpleJavaFileObject(URI.create("byte:///" + className + kind.extension), kind) {
                @Override
                public OutputStream openOutputStream() {
                    return bytecodeOutput;
                }
            };
        } else {
            return super.getJavaFileForOutput(location, className, kind, sibling);
        }
    }
}
----------------------------------------------------------------

class DynamicClassLoader extends ClassLoader {
        public Class<?> loadClass(String name, byte[] bytecode) {
            return defineClass(name, bytecode, 0, bytecode.length);               //here i got the error
        }
    }

what's wrong with it?

[Paul Clapham]

I don't see any code which actually writes bytes to an output stream, but my guess is that it's writing the bytes one buffer at a time and not paying attention to the fact that the last buffer may not be totally full. So I'd suggest drilling down in the code until you find where that's being done.

[Ron McLeod]

In addition to what Paul said, I would eyeball the values in the byte array and check:
  - that the array begins with the magic number 0xCAFEBABE
  - if there is anything odd near the end of the array like a series of zero values or a string of bytes which also appeared earlier-on on the array which might indicate that the whole buffer was written to the file and not just the portion of it needed for the last write (Paul's guess)
  - for ASCII text (other than String constants which may have been in the source) which may have been written to the output of an error occurred during complication