Dynamically generate Java code (1)

Bcel is Bytecode Engineering Library, which is a third-party byte code generation library that can help us directly generate Java bytecodes directly in memory. BCEL is a source code open free code base (http://sourceforge.net/projects/bcel/), can help us analyze, create, and process binary Java bytecodes. This article will explain any BCEL to dynamically generate Java code.

/ *

* Create a date 2004-7-2

* Create a human hongsoft

* File name Testbcel.java

* /

Package com.hongsoft.test;

Import java.io. *;

Import java.util.stack;

// Download BCEL Code Base from SourceForge.Net/Projects/bcel/

Import de.Fub.bytecode.classfile. *;

Import de.Fub.bytecode.Generic. *;

Import de.fub.bytecode.constants;

Public Class Testbcel Extends ClassLoader {

Private Object O;

Public static void main (String [] args) {

New testbcel ();

}

Public Testbcel ()

{

// Declaration, Trouble_ticket is a class name, super class is java.lang.object

// ACC represents Access, new string [] {} is an array of interfaces it wants to implement

// Effect: public Trouble_ticket {}

Classgen Classgen

= New Classgen ("Trouble_ticket", "Java.lang.Object", "", constants.acc_public | constants.acc_super, new string [] {});

// constant pool

ConstantPoolgen CP = Classgen.getConstantPool ();

// Construct attribute, effect: public string creater = "";

Fieldgen FG = New Fieldgen (constants.acc_public, type.string, "creater", cp);

// Add Field

Classgen.addfield (fg.getfield ());

// Constructor Classgen.adDemptyConstructor (constants.acc_public);

// Byte form

BYTE [] DATA = Classgen.getjavaclass (). getBytes ();

// Generate a class

Class C = DefineClass (Data, 0, Data.Length);

Try {

o = c.newinstance ();

// program effect

System.out.println (O.GetClass (). Getname ());

System.out.println (O.GetClass (). Getfield ("create"). GetName ());

System.out.println (Classgen.Getfields (). Length);

} catch (IllegaCcessException E) {

Throw new runtimeException (E.GetMessage ());

} catch (exception e) {

Throw new runtimeException (E.getMessage ());

}

}

The procedure run is as follows:

Trouble_ticket

Creater

1