// 类库, jvm中所加载的classClassPool pool = ClassPool.getDefault();// 加载一个已知的类, 注：参数必须为全量类名CtClass ctClass = pool.get("com.itheima.Student");// 创建一个新的类, 类名必须为全量类名CtClass tClass = pool.makeClass("com.itheima.Calculator");

// 获取已知类的属性CtField ctField = ctClass.getDeclaredField("name");// 构建新的类的成员变量CtField ctFieldNew = new CtField(CtClass.intType,"age",ctClass);// 设置类的访问修饰符为publicctFieldNew.setModifiers(Modifier.PUBLIC);// 将属性添加到类中ctClass.addField(ctFieldNew);

// 获取已有方法//创建新的方法, 参数1:方法的返回类型，参数2：名称，参数3：方法的参数，参数4：方法所属的类CtMethod ctMethod = new CtMethod(CtClass.intType, "calc", new CtClass[]
{CtClass.intType,CtClass.intType}, tClass);// 设置方法的访问修饰ctMethod.setModifiers(Modifier.PUBLIC);// 将新建的方法添加到类中ctClass.addMethod(ctMethod);// 方法体内容代码 $1代表第一个参数，$2代表第二个参数ctMethod.setBody("return $1 + $2;"); CtMethod ctMethod = ctClass.getDeclaredMethod("sayHello");

// 获取已有的构造方法, 参数为构建方法的参数类型数组CtConstructor ctConstructor = ctClass.getDeclaredConstructor(new CtClass[]{});// 创建新的构造方法CtConstructor ctConstructor = new CtConstructor(new CtClass[]{CtClass.intType},ctClass); ctConstructor.setModifiers(Modifier.PUBLIC);ctConstructor.setBody("this.age = $1;");ctClass.addConstructor(ctConstructor);// 也可直接创建ctConstructor = CtNewConstructor.make("public Student(int age){this.age=age;}", ctClass);

public class User {private String name;public User() {}public User(String name) {this.name = name;}public String sayJavassist() {return "Hello Javassist";}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +'}';}
}

// 类库池, jvm中所加载的classClassPool pool = ClassPool.getDefault();// 获取指定的Student类CtClass ctClass = pool.get("com.example.test.User");// 获取sayHello方法CtMethod ctMethod = ctClass.getDeclaredMethod("sayJavassist");// 在方法的代码后追加 一段代码ctMethod.insertAfter("System.out.println(\"I'm Javassist.\");");// 使用当前的ClassLoader加载被修改后的类Class<?> newClass = ctClass.toClass();User user = (User) newClass.newInstance();System.out.println(user.sayJavassist());

// 类库池, jvm中所加载的classClassPool pool = ClassPool.getDefault();// 获取指定的Student类CtClass ctClass = pool.get("com.example.test.User");// 增加方法CtMethod ctMethod = new CtMethod(CtClass.intType, "getAgeSum",new CtClass[]{CtClass.intType, CtClass.intType}, ctClass);// 设置方法的访问修饰ctMethod.setModifiers(Modifier.PUBLIC);// 设置方法体代码ctMethod.setBody("return $1 + $2;");// 添加新建的方法到原有的类中ctClass.addMethod(ctMethod);// 加载修改后的类ctClass.toClass();// 创建对象User stu = new User();// 获取calc方法Method dMethod = User.class.getDeclaredMethod("getAgeSum", new Class[]{int.class, int.class});// 反射调用 方法Object result = dMethod.invoke(stu, 10, 20);System.out.println(result);

// 类库池, jvm中所加载的classClassPool pool = ClassPool.getDefault();// 创建一个学校类CtClass schoolClass = pool.makeClass("com.example.test.School");// 设置为公有类schoolClass.setModifiers(Modifier.PUBLIC);// 获取String类型CtClass stringClass = pool.get("java.lang.String");// 获取list类型CtClass listClass = pool.get("java.util.List");// 获取学生的类型CtClass userClass = pool.get("com.example.test.User");// 给学校添加一个校名属性CtField nameField = new CtField(stringClass, "schoolName", schoolClass);nameField.setModifiers(Modifier.PUBLIC);schoolClass.addField(nameField);// 给学校添加一个学生集合CtField studentList = new CtField(listClass, "users", schoolClass);studentList.setModifiers(Modifier.PUBLIC);schoolClass.addField(studentList);// 给学校一个空构造CtConstructor ctConstructor = CtNewConstructor.make("public School() " +"{this.schoolName=\"湖畔小学\";this.users = new java.util.ArrayList();}", schoolClass);schoolClass.addConstructor(ctConstructor);// 给学校一个addUser的方法CtMethod m = new CtMethod(CtClass.voidType, "addUser", new CtClass[]{userClass}, schoolClass);m.setModifiers(Modifier.PUBLIC);// 添加学生对象到students属性中, $1代表参数1m.setBody("this.users.add($1);");schoolClass.addMethod(m);// 给学校添加一个介绍的方法CtMethod introduce = new CtMethod(CtClass.voidType, "introduce", new CtClass[]{}, schoolClass);introduce.setBody("System.out.println(\"The School name is \" + this.schoolName);");introduce.insertAfter("System.out.println(this.users);");schoolClass.addMethod(introduce);// 加载修改后的学校Class<?> schoolLoadClass = schoolClass.toClass();// 构建一个学校(空构造)Object school = schoolLoadClass.newInstance();// 获取添加用户方法Method addUserMethod = schoolLoadClass.getDeclaredMethod("addUser", userClass.toClass());addUserMethod.invoke(school, new User("小明"));addUserMethod.invoke(school, new User("小张"));// 获取介绍方法，把刚才的信息给打印处理Method introduceMethod = school.getClass().getDeclaredMethod("introduce");introduceMethod.invoke(school);