javassist example

create a class with two fields "name" and "value"

create an constructor with parameters

create an method with parameters to print something

注意field安装的顺序是从后向前的

最先addField的参数，在constructor中出现在最末尾

TBD: 如何构建不同的constructor?

ct.writeFile();  //耗时16ms, 其他可忽略

where is class loading???

package javassisttest;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import javassist.*;

public class JavaAssistExample {


	public static void main(String[] args) {
		ClassPool classPool = ClassPool.getDefault();
		CtClass ct = classPool.makeClass("FakeClass");
		DateFormat df = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss.SSS");
		try {			
		    CtField field;
		    
		    field = new CtField(classPool.get(Integer.class.getName()), "value", ct);
		    field.setModifiers(Modifier.PUBLIC);  
		    ct.addMethod(CtNewMethod.setter("setValue", field));  
		    ct.addMethod(CtNewMethod.getter("getValue", field));  
		    ct.addField(field);  

		    field = new CtField(classPool.get(String.class.getName()), "name", ct);
		    field.setModifiers(Modifier.PUBLIC);  
		    ct.addMethod(CtNewMethod.setter("setName", field));  
		    ct.addMethod(CtNewMethod.getter("getName", field));  
		    ct.addField(field);  			

			CtClass[] constrParam = new CtClass[2];
			constrParam[0] = classPool.get(String.class.getName());
			constrParam[1] = classPool.get(Integer.class.getName());
			CtConstructor constructor = new CtConstructor(constrParam, ct);  
		    constructor.setModifiers(Modifier.PUBLIC);  		    
		    constructor.setBody("{this.name=$1; this.value=$2;}");  
		    ct.addConstructor(constructor);  
			
			CtClass[] methodParam = new CtClass[2];
			methodParam[0] = classPool.get(String.class.getName());
			methodParam[1] = classPool.get(Integer.class.getName());
			
//		    CtMethod m = CtNewMethod
//					.make("public void pp1() { System.out.println(\"Hello     World\");}",
//							ct);
//			ct.addMethod(m);

		    CtMethod method = new CtMethod(CtClass.booleanType, "printall", methodParam, ct);  
		    method.setModifiers(Modifier.PUBLIC);  
//		    method.setBody("{System.out.println(\"name:\" + this.name + \",value:\" + this.value);  return true;}");  
		    method.setBody("{System.out.println(\"name:\" + $1 + \",value:\" + $2);  return true;}");  
		    ct.addMethod(method);  
			
			System.out.println("--1" + df.format(new Date()));
			ct.writeFile();
			System.out.println("--2" + df.format(new Date()));
			Class<?> clazz = ct.toClass(); 
			System.out.println("--3" + df.format(new Date()));
			Object o = clazz.getConstructor(new Class[]{String.class,Integer.class}).newInstance("myname", 123);
			System.out.println("--4" + df.format(new Date()));
			Method mm = o.getClass().getMethod("printall", new Class[] {String.class, Integer.class});  
			System.out.println("--5" + df.format(new Date()));
			mm.invoke(o, "fff", 34); 
			System.out.println("--6" + df.format(new Date()));
		} catch (CannotCompileException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InstantiationException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
}

output

--12015/06/12 10:40:03.177
--22015/06/12 10:40:03.193
--32015/06/12 10:40:03.193
--42015/06/12 10:40:03.193
--52015/06/12 10:40:03.193
name:fff,value:34
--62015/06/12 10:40:03.193