Dynamically generate Java code
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 {
?????prate object o;
??? public static void? main (string [] args) {
??????? new testbcel (); ??????
}
?
??? public? testbcel ()
?????? {
?????????? ??????
?????????????? // declared class, trouble_ticket is a class name, superclass 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, "java.lang.object", "", ??????? ?? constants.acc_public | Constants.acc_super, new string [] {};
???????
?????????????? // constant pool
ConstantPoolgen CP = Classgen.getConstantPool ();
????
?????????????????? // constructor, effect: public string creater = ""
????????????? ?? fieldgen fg = new fieldgen (constants.acc_public, type.string, ??????????? ?? "Creater", CP);
?????????????????? // joined FIELD
????????????? ?? Classgen.Addfield (fg.getfield ());
??????
???????????????????? ? // Constructor?????????????????? ? ?????? ???????????? ?? Classgen.adDemptyconstructor (constants.acc_public);
?????????????????????? // Byte form
???????????????????????. Byte [] Data = Classgen.getjavaclass ().
????????????????????? // generated
?????????????????????? 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 ("creater"). GetName ());?? ? ????????????????????
???????????????????????? system.out.println (Classgen.Getfields (). Length);
???????????????????????????????} catch (IllegalaccessException E) {
??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????.
???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????} Catch (Exception E) {
??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????.
??????????????????????}
??????}
???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
}
The procedure run is as follows:
Trouble_ticket
Creater
1
