动态修改实体class类注释中的值

import java.lang.reflect.Method;

import javassist.ClassPool;
import javassist.CtClass;
import javassist.bytecode.AnnotationsAttribute;
import javassist.bytecode.ClassFile;
import javassist.bytecode.ConstPool;
import javassist.bytecode.annotation.Annotation;
import javassist.bytecode.annotation.ArrayMemberValue;
import javassist.bytecode.annotation.BooleanMemberValue;
import javassist.bytecode.annotation.IntegerMemberValue;
import javassist.bytecode.annotation.MemberValue;
import javassist.bytecode.annotation.StringMemberValue;

/**  
 * @Title: ClassPoolUtils.java
 * @Package com.sgfm.scsm.util
 * @Description: 动态修改实体类注释中的值(不提倡经常使用)
 * @author TangCai
 * @date 2016年11月16日 下午3:08:56
 * @version V1.0  
 */
public class ClassPoolUtils {
	/** 
     * 运行时动态ORM表映射 
     * @param entityClass   实体类
     * @param annotation    注释类
     * @param atMethodName  注释类方法
     * @param atMethodVal   注释类方法的更新值
     * @return              修改注释值后实体类 
     */  
    @SuppressWarnings("unchecked")
	public static Class setPool(Class entityClass, Class annotation,
    		String atMethodName, Object atMethodVal){  
        Class c = null;
        try {  
            ClassPool classPool = ClassPool.getDefault();  

            CtClass clazz = classPool.getCtClass(entityClass.getName());
            ClassFile classFile = clazz.getClassFile();
            //clazz.freeze();//冻结

            ConstPool constPool = classFile.getConstPool();  
            Class cl = (Class)annotation;
            Annotation newAnnotation = createJavassistAnnotation(constPool,entityClass.getAnnotation(cl),atMethodName,atMethodVal);
            
            AnnotationsAttribute attribute = (AnnotationsAttribute)classFile.getAttribute(AnnotationsAttribute.visibleTag);  
            attribute.addAnnotation(newAnnotation);  
            classFile.addAttribute(attribute); 
            ClassLoader parent = entityClass.getClassLoader();
            EntityClassLoader loader = new ClassPoolUtils().new EntityClassLoader(parent);
            //clazz.toClass();//同一个ClassLoader不能多次加载同一个类
            c = clazz.toClass(loader , null);//替换Class的时候，  加载该Class的ClassLoader也必须用新的
            //clazz.defrost();//解除冻结
            clazz.detach(); //注销class
        } catch (Exception e) {  
            e.printStackTrace();  
        }  
        return c;  
    }
    public static Annotation createJavassistAnnotation(ConstPool constpool,
    		java.lang.annotation.Annotation annotation,String atMethodName, Object atMethodVal) throws Exception {
    	Annotation annotationCopy = new Annotation(annotation.annotationType().getName(), constpool);
    	String typeName = null;
    	MemberValue mv = null;
    	for (Method m : annotation.annotationType().getDeclaredMethods()) {
    			Object value = m.invoke(annotation);
    			typeName = m.getReturnType().getSimpleName();
    			if(atMethodName.equals(m.getName())) value = atMethodVal;
    			if(typeName.equals("int"))
    				mv = new IntegerMemberValue(constpool,(Integer)value);
    			else if(typeName.equals("String[]")){
    				String[] stres = (String[])value;
    	            StringMemberValue[] elements = new StringMemberValue[stres.length];
    	            for(int i=0;i loadClass(String name) throws ClassNotFoundException {  
             return this.loadClass(name, false);  
         }  
         
         @Override  
         protected synchronized Class loadClass(String name, boolean resolve)  
                 throws ClassNotFoundException {
             Class clazz = this.findLoadedClass(name);  
             if(null != parent)
                 clazz = parent.loadClass(name);    
             if(null == clazz)
                 this.findSystemClass(name);  
             if(null == clazz)
                 throw new ClassNotFoundException();  
             if(null != clazz && resolve)
                 this.resolveClass(clazz);
             return clazz;  
         }  
    }
}