javassist初接觸

直接上代碼：

pom增長依賴：

    <dependency>
    <groupId>org.javassist</groupId>
    <artifactId>javassist</artifactId>
    <version>3.18.2-GA</version>
</dependency>

寫個Hello類：

package JavassistTest.JavassistTest;

public class Hello {

    public void sayHello(){
        System.out.println("Hello world");
    }
}

主類：

package JavassistTest.JavassistTest;

import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.CtNewMethod;
import javassist.NotFoundException;

/**
 * Hello world!
 *
 */
public class App {
    public static void main(String[] args) throws NotFoundException,
            CannotCompileException, InstantiationException, IllegalAccessException, ClassNotFoundException {
        
        //~加上報錯，和類加載有關係，這裏new的話會把Hello類加載，以後再加載的話就會報錯
        //Hello hell=new Hello();
        //hell.sayHello();
        //~
        
        
        
        CtClass ctClass = ClassPool.getDefault().getCtClass("JavassistTest.JavassistTest.Hello");
        
        
        CtMethod ctMethod = ctClass.getDeclaredMethod("sayHello");
        ctMethod.setBody("System.out.println(\"hi\");");    
        
        
        Class ch=ctClass.toClass();
        
        Hello h=(Hello) ch.newInstance();
        h.sayHello();        
        
        Hello hel=new Hello();
        hel.sayHello();


    }
}

輸出結果：

hi
hi

結果同樣，說明是class被修改了。