javassist.bytecode

Class ClassFileWriter

java.lang.Object

javassist.bytecode.ClassFileWriter

public class ClassFileWriter
extends Object

A quick class-file writer. This is useful when a generated class file is simple and the code generation should be fast.

Example:

 ClassFileWriter cfw = new ClassFileWriter(ClassFile.JAVA_4, 0);
 ConstPoolWriter cpw = cfw.getConstPool();

 FieldWriter fw = cfw.getFieldWriter();
 fw.add(AccessFlag.PUBLIC, "value", "I", null);
 fw.add(AccessFlag.PUBLIC, "value2", "J", null);

 int thisClass = cpw.addClassInfo("sample/Test");
 int superClass = cpw.addClassInfo("java/lang/Object");

 MethodWriter mw = cfw.getMethodWriter();

 mw.begin(AccessFlag.PUBLIC, MethodInfo.nameInit, "()V", null, null);
 mw.add(Opcode.ALOAD_0);
 mw.add(Opcode.INVOKESPECIAL);
 int signature = cpw.addNameAndTypeInfo(MethodInfo.nameInit, "()V");
 mw.add16(cpw.addMethodrefInfo(superClass, signature));
 mw.add(Opcode.RETURN);
 mw.codeEnd(1, 1);
 mw.end(null, null);

 mw.begin(AccessFlag.PUBLIC, "one", "()I", null, null);
 mw.add(Opcode.ICONST_1);
 mw.add(Opcode.IRETURN);
 mw.codeEnd(1, 1);
 mw.end(null, null);

 byte[] classfile = cfw.end(AccessFlag.PUBLIC, thisClass, superClass,
                            null, null);
 

The code above generates the following class:

 package sample;
 public class Test {
     public int value;
     public long value2;
     public Test() { super(); }
     public one() { return 1; }
 }
 

Since:

3.13

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	ClassFileWriter.AttributeWriter This writes attributes.
static class	ClassFileWriter.ConstPoolWriter Constant Pool.
static class	ClassFileWriter.FieldWriter Field.
static class	ClassFileWriter.MethodWriter Method.

Constructor Summary

Constructors

Constructor and Description
ClassFileWriter(int major, int minor) Constructs a class file writer.

Method Summary

Methods

Modifier and Type	Method and Description
void	end(DataOutputStream out, int accessFlags, int thisClass, int superClass, int[] interfaces, ClassFileWriter.AttributeWriter aw) Ends writing and writes the contents of the class file into the given output stream.
byte[]	end(int accessFlags, int thisClass, int superClass, int[] interfaces, ClassFileWriter.AttributeWriter aw) Ends writing and returns the contents of the class file.
ClassFileWriter.ConstPoolWriter	getConstPool() Returns a constant pool.
ClassFileWriter.FieldWriter	getFieldWriter() Returns a filed writer.
ClassFileWriter.MethodWriter	getMethodWriter() Returns a method writer.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ClassFileWriter

public ClassFileWriter(int major,
               int minor)

Constructs a class file writer.

Parameters:

major - the major version (ClassFile.JAVA_4, ClassFile.JAVA_5, ...).

minor - the minor version (0 for JDK 1.3 and later).

Method Detail

getConstPool

public ClassFileWriter.ConstPoolWriter getConstPool()

Returns a constant pool.

getFieldWriter

public ClassFileWriter.FieldWriter getFieldWriter()

Returns a filed writer.

getMethodWriter

public ClassFileWriter.MethodWriter getMethodWriter()

Returns a method writer.

end

public byte[] end(int accessFlags,
         int thisClass,
         int superClass,
         int[] interfaces,
         ClassFileWriter.AttributeWriter aw)

Ends writing and returns the contents of the class file.

Parameters:

accessFlags - access flags.

thisClass - this class. an index indicating its CONSTANT_Class_info.

superClass - super class. an index indicating its CONSTANT_Class_info.

interfaces - implemented interfaces. index numbers indicating their ClassInfo. It may be null.

aw - attributes of the class file. May be null.

See Also:

AccessFlag

end

public void end(DataOutputStream out,
       int accessFlags,
       int thisClass,
       int superClass,
       int[] interfaces,
       ClassFileWriter.AttributeWriter aw)
         throws IOException

Ends writing and writes the contents of the class file into the given output stream.

Parameters:

accessFlags - access flags.

thisClass - this class. an index indicating its CONSTANT_Class_info.

superClass - super class. an index indicating its CONSTANT_Class_info.

interfaces - implemented interfaces. index numbers indicating their CONSTATNT_Class_info. It may be null.

aw - attributes of the class file. May be null.

Throws:

IOException

See Also:

AccessFlag