Examples of org.springframework.asm.ClassWriter

org.springframework.asm.ClassWriter
A {@link ClassVisitor} that generates classes in bytecode form. Moreprecisely this visitor generates a byte array conforming to the Java class file format. It can be used alone, to generate a Java class "from scratch", or with one or more {@link ClassReader ClassReader} and adapter class visitorto generate a modified class from one or more existing Java classes. @author Eric Bruneton


    private static byte[] generateByteCodeForInterface(final String interfaceName, Class<?>... interfacesToImplement) {


      String interfaceResourcePath = ClassUtils.convertClassNameToResourcePath(interfaceName);


      ClassWriter cw = new ClassWriter(0);
      cw.visit(V1_6, ACC_PUBLIC + ACC_ABSTRACT + ACC_INTERFACE, interfaceResourcePath, null, "java/lang/Object",
          toResourcePaths(interfacesToImplement));
      cw.visitSource(interfaceResourcePath + ".java", null);
      cw.visitEnd();


      return cw.toByteArray();
    }

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   */
  @SuppressWarnings("unchecked")
  private Class<? extends CompiledExpression> createExpressionClass(SpelNodeImpl expressionToCompile) {
    // Create class outline 'spel/ExNNN extends org.springframework.expression.spel.CompiledExpression'
    String clazzName = "spel/Ex" + getNextSuffix();
    ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS|ClassWriter.COMPUTE_FRAMES);
    cw.visit(V1_5, ACC_PUBLIC, clazzName, null, "org/springframework/expression/spel/CompiledExpression", null);


    // Create default constructor
    MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
    mv.visitCode();
    mv.visitVarInsn(ALOAD, 0);
    mv.visitMethodInsn(INVOKESPECIAL, "org/springframework/expression/spel/CompiledExpression",
        "<init>", "()V", false);
    mv.visitInsn(RETURN);
    mv.visitMaxs(1, 1);
    mv.visitEnd();


    // Create getValue() method
    mv = cw.visitMethod(ACC_PUBLIC, "getValue",
        "(Ljava/lang/Object;Lorg/springframework/expression/EvaluationContext;)Ljava/lang/Object;", null,
        new String[ ]{"org/springframework/expression/EvaluationException"});
    mv.visitCode();


    CodeFlow cf = new CodeFlow(clazzName, cw);


    // Ask the expression AST to generate the body of the method
    try {
      expressionToCompile.generateCode(mv, cf);
    }
    catch (IllegalStateException ex) {
      if (logger.isDebugEnabled()) {
        logger.debug(expressionToCompile.getClass().getSimpleName() +
            ".generateCode opted out of compilation: " + ex.getMessage());
      }
      return null;
    }


    CodeFlow.insertBoxIfNecessary(mv, cf.lastDescriptor());
    if ("V".equals(cf.lastDescriptor())) {
      mv.visitInsn(ACONST_NULL);
    }
    mv.visitInsn(ARETURN);


    mv.visitMaxs(0, 0);  // not supplied due to COMPUTE_MAXS
    mv.visitEnd();
    cw.visitEnd();
    
    cf.finish();
    
    byte[] data = cw.toByteArray();
    // TODO need to make this conditionally occur based on a debug flag
    // dump(expressionToCompile.toStringAST(), clazzName, data);
    return (Class<? extends CompiledExpression>) this.ccl.defineClass(clazzName.replaceAll("/", "."), data);
  }

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    // translate internal name to binary form
    return classLoader.loadClass(classInternalName.replace('/', '.'), bytecode);
  }


  byte[] generateClassBytecode(String className, Class<? extends DataSerializable> clazz, int classId) {
    ClassWriter cw = new ClassWriter(0);


    cw.visit(V1_5, ACC_PUBLIC + ACC_SUPER, className, null, INSTANTIATOR_NAME, new String[] { SERIALIZABLE_NAME });
    FieldVisitor fv = cw.visitField(ACC_PRIVATE + ACC_FINAL + ACC_STATIC, CLASS_FIELD_NAME, CLASS_DESCRIPTOR, null,
        null);
    fv.visitEnd();
    fv = cw.visitField(ACC_PRIVATE + ACC_FINAL + ACC_STATIC, ID_FIELD_NAME, Type.INT_TYPE.getDescriptor(), null,
        Integer.valueOf(classId));
    fv.visitEnd();


    String voidNoArgMethodDescriptor = Type.getMethodDescriptor(Type.VOID_TYPE, new Type[] {});


    // field class loading
    MethodVisitor mv = cw.visitMethod(ACC_STATIC, CINIT, voidNoArgMethodDescriptor, null, null);
    mv.visitCode();
    mv.visitLdcInsn(Type.getType(clazz));
    mv.visitFieldInsn(PUTSTATIC, className, CLASS_FIELD_NAME, CLASS_DESCRIPTOR);
    mv.visitInsn(RETURN);
    mv.visitMaxs(1, 0);
    mv.visitEnd();


    String voidArgClassAndIntDescriptor = Type.getMethodDescriptor(Type.VOID_TYPE, new Type[] {
        Type.getType(Class.class), Type.INT_TYPE });


    // default constructor
    mv = cw.visitMethod(ACC_PUBLIC, INIT, voidNoArgMethodDescriptor, null, null);
    mv.visitCode();
    mv.visitVarInsn(ALOAD, 0);
    mv.visitFieldInsn(GETSTATIC, className, CLASS_FIELD_NAME, CLASS_DESCRIPTOR);
    mv.visitFieldInsn(GETSTATIC, className, ID_FIELD_NAME, Type.INT_TYPE.getDescriptor());
    mv.visitMethodInsn(INVOKESPECIAL, className, INIT, voidArgClassAndIntDescriptor);
    mv.visitInsn(RETURN);
    mv.visitMaxs(3, 1);
    mv.visitEnd();


    // two-arg constructor
    mv = cw.visitMethod(ACC_PUBLIC, INIT, voidArgClassAndIntDescriptor, null, null);
    mv.visitCode();
    mv.visitVarInsn(ALOAD, 0);
    mv.visitVarInsn(ALOAD, 1);
    mv.visitVarInsn(ILOAD, 2);
    mv.visitMethodInsn(INVOKESPECIAL, INSTANTIATOR_NAME, INIT, voidArgClassAndIntDescriptor);
    mv.visitInsn(RETURN);
    mv.visitMaxs(3, 3);
    mv.visitEnd();


    Type customClassType = Type.getType(clazz);
    String customTypeNoArgDesc = Type.getMethodDescriptor(customClassType, new Type[] {});


    // newInstance overloaded method
    mv = cw.visitMethod(ACC_PUBLIC, NEW_INSTANCE, customTypeNoArgDesc, null, null);


    mv.visitCode();
    mv.visitTypeInsn(NEW, customClassType.getInternalName());
    mv.visitInsn(DUP);
    mv.visitMethodInsn(INVOKESPECIAL, customClassType.getInternalName(), INIT, voidNoArgMethodDescriptor);
    mv.visitInsn(ARETURN);
    mv.visitMaxs(2, 1);
    mv.visitEnd();


    // plus original method signature
    mv = cw.visitMethod(ACC_PUBLIC + ACC_BRIDGE + ACC_SYNTHETIC, NEW_INSTANCE, NEW_INSTANCE_DESC, null, null);
    mv.visitCode();
    mv.visitVarInsn(ALOAD, 0);
    mv.visitMethodInsn(INVOKEVIRTUAL, className, NEW_INSTANCE, customTypeNoArgDesc);
    mv.visitInsn(ARETURN);
    mv.visitMaxs(1, 1);
    mv.visitEnd();


    // end class generation
    cw.visitEnd();


    return cw.toByteArray();
  }

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