Reference code :github.com/ZhangXiaoix…
Springboot version (look for the Java-Base branch)gitee.com/zhang-xiao-…
Collection of online information, their own collation collection
Video tutorial (Tencent Classroom): ke.qq.com/webcourse/i… Video tutorial (netease Cloud Classroom): https://study.163.com/course/courseLearn.htm?courseId=1005927016#/learn/video?lessonId=1053358058&courseId=1005927016
1: Get the class by reflection
package com.example.java.base.reflect; import org.junit.Test; import java.lang.reflect.Constructor; import java.lang.reflect.Field; import java.lang.reflect.Method; import java.util.Objects; /** ** ReflectDemo01: ReflectTest class correlation ** @author zhangxiaoxiang * @date 2020/11/3 */ public class ReflectTest {/** * */ public static void demo01() {try {Class<? > perClazz = Class.forName("com.example.java.base.reflect.Person"); System.out.println(" method 1===> through class.forname (\" full name \")\t" + perClazz); } catch (ClassNotFoundException e) { e.printStackTrace(); } Class<? > perClazz2 = Person.class; System.out.println(" type 2===> class name. Class \t" + perClazz2); Person per = new Person(); Class<? > perClazz3 = per.getClass(); System.out.println(" method 3===> object.getClass ()\t" + perClazz3); } /** * public static Class<? > getClassTest() {//Class entry Class<? > perClazz = null; try { perClazz = Class.forName("com.example.java.base.reflect.Person"); return perClazz; } catch (ClassNotFoundException e) { e.printStackTrace(); return null; Throws IllegalAccessException; throws IllegalAccessException; throws IllegalAccessException; InstantiationException {//Class entry Class<? > perClazz = getClassTest(); // Get all public methods (1. All methods in this class and its parent class and interface 2. Conforms to the law of access modifiers), pay attention to the null pointer System. Out. The println (" = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = access method (all) = = = = = = = = = = = = = = = = = = = = = = = = = = = "); Method[] methods = Objects.requireNonNull(perClazz).getMethods(); System.out.println(" public method =========="); for (Method method : methods) { System.out.println(method); } system.out.println (" all methods =========="); / / get all the methods of the current class (1) only the current class (2) ignore access modifier) Method [] declaredMethods = perClazz. GetDeclaredMethods (); for (Method declaredMethod : declaredMethods) { System.out.println(declaredMethod); } System. Out. Println (" = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = obtain all interface = = = = = = = = = = = = = = = = = = = = = = = = = = = "); Class<? >[] interfaces = perClazz.getInterfaces(); for (Class<? > inter : interfaces) { System.out.println(inter); } System. Out. Println (" = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = obtain all parent class = = = = = = = = = = = = = = = = = = = = = = = = = = = "); Class<? > superclass = perClazz.getSuperclass(); System.out.println(superclass); System. The out. Println (" = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = obtain all constructors = = = = = = = = = = = = = = = = = = = = = = = = = = = "); Constructor<? >[] constructors = perClazz.getConstructors(); for (Constructor<? > constructor : constructors) { System.out.println(constructor); } System. Out. Println (" = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = obtain all constructors = = = = = = = = = = = = = = = = = = = = = = = = = = = "); for (Constructor<? > constructor : constructors) { System.out.println(constructor); } System. Out. Println (" = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = all the attributes (such as public and private) = = = = = = = = = = = = = = = = = = = = = = = = = = = "); System.out.println(" all public attributes ===="); Field[] fields = perClazz.getFields(); for (Field field : fields) { System.out.println(field); } system.out.println (" all attributes (attributes: public attributes)===="); Field[] declaredFields = perClazz.getDeclaredFields(); for (Field declaredField : declaredFields) { System.out.println(declaredField); } System. Out. Println (" = = = = = = = = = = = = = = = = = = = = = = = = = = = = type (interface) for current reflection represents the object (instance) = = = = = = = = = = = = = = = = = = = = = = = = = = = "); Object instance = perClazz.newInstance(); Person per = (Person) instance; per.interface2Method(); } /** * Test ** @instantiationException 1 * @throws IllegalAccessException 2 */ @test public void test2() throws InstantiationException, IllegalAccessException {System. Out. Println (" * * * * * * * * * * * * * * * * * * * * * * * * get reflection object mode of three kinds of * * * * * * * * * * * * * * * * * * * * * * * * "); demo01(); System. Out. Println (" * * * * * * * * * * * * * * * * * * * * * * * * reflection other information * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * "); demo02(); }}Copy the code2 Operation after obtaining the reflection class instance
package com.example.java.base.reflect;
import org.junit.Test;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Objects;
import java.util.Properties;
/**
* ReflectDemo02:反射获取类的实例,并操作
*
* @author zhangxiaoxiang
* @date 2020/11/3
*/
public class Reflect2Test {
/**
* 为了方便,这里定义一个方法获取反射,方便后面测试,这里使用的方式一为示例
*
* @return 获取到的反射对象
*/
public static Class<?> getClassTest() {
Class<?> perClazz = null;
try {
perClazz = Class.forName("com.example.java.base.reflect.Person");
return perClazz;
} catch (ClassNotFoundException e) {
e.printStackTrace();
return null;
}
}
/**
* 获取对象的实例，并操作对象
*
* @throws InstantiationException
* @throws IllegalAccessException
*/
public static void demo01() throws IllegalAccessException, InstantiationException, NoSuchFieldException,
NoSuchMethodException, InvocationTargetException, IOException {
Class<?> perClazz = getClassTest();
Person per = (Person) Objects.requireNonNull(perClazz).newInstance();
per.setId(1);
per.setName("zs");
per.setAge(23);
per.setDesc("我是描述属性");
System.out.println("===============================为对象赋值============================================");
System.out.println(per.toString());
System.out.println("===============================操作属性============================================");
Field idField = perClazz.getDeclaredField("id");
//访问的是private修饰的id，但是private是私有
//修改属性的访问权限 使用反射时，如果 因为访问修饰符限制造成异常，可以通过 Field/Method/Constructor.setAccessible(true)
idField.setAccessible(true);
//per.setId(1);
idField.set(per, 2);
System.out.println("修改私有属性后:"+per.toString());
Method method = perClazz.getDeclaredMethod("privateMethodTest", null);
method.setAccessible(true);
//方法的调用：invoke()
method.invoke(per, null);
//per.say(xxx);
Method method2 = perClazz.getDeclaredMethod("privateMethodTest", String.class);
method2.setAccessible(true);
method2.invoke(per, "我是pram");
System.out.println("===============================操作构造方法============================================");
// Constructor<?>[] constructors = perClazz.getConstructors() ;//公共
// for(Constructor constructor:constructors) {
// System.out.println(constructor);
// }
// Constructor<?>[] constructors = perClazz.getDeclaredConstructors() ;//本类
// for(Constructor constructor:constructors) {
// System.out.println(constructor);
// }
//获取指定的构造方法
//在反射中，根据类型 获取方法时：基本类型（int、char...）和包装类(Integer,Character)是不同的类型
// Constructor<?> constructor = perClazz.getConstructor(Integer.class);
Constructor<?> constructor = perClazz.getConstructor(int.class);
System.out.println("获取指定的构造方法===>"+constructor);
Constructor<?> constructor2 = perClazz.getDeclaredConstructor(String.class);
System.out.println("获取指定的构造方法===>"+constructor2);
//Person per = new Person() ;
//根据获取的private构造方法，获取对象实例
constructor2.setAccessible(true);
Person per3 = (Person) constructor2.newInstance("zs");
System.out.println("获取带有String的构造方法" + per3);
//因为constructor是 有参构造方法(Integer还是int这里构造的就是什么值)
Person instance2 = (Person) constructor.newInstance(23);
System.out.println("获取带有Integer的构造方法" +instance2);
Constructor<?> constructor3 = perClazz.getConstructor();
//因为constructor3是 无参构造方法，因此不需要传值
Person instance = (Person) constructor3.newInstance();
System.out.println("无参构造"+instance);
System.out.println("===============================动态加载 类名 和方法===============================");
Properties prop = new Properties();
prop.load(new FileReader("src/main/resources/class.txt"));
String classname = prop.getProperty("classname");
String methodname = prop.getProperty("methodname");
Class<?> perClazz1 = null;
try {
perClazz1 = Class.forName(classname);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
method = perClazz1.getMethod(methodname);
System.out.println("===>反射读取配置文件并调用");
method.invoke(perClazz1.newInstance());
System.out.println("===============================反射可以 越过泛型检查===============================");
System.out.println("虽然可以通过反射 访问private等访问修饰符不允许访问的属性/方法，也可以忽略掉泛型的约束;" +
"但实际开发 不建议这样使用，因此可能造成程序的混乱。");
ArrayList<Integer> list = new ArrayList<>();
list.add(123);
list.add(3);
list.add(2);
// list.add("zs") ;
Class<?> listClazz = list.getClass();
method = listClazz.getMethod("add", Object.class);
method.invoke(list, "zs...");
System.out.println("反射可以 越过泛型检查===>"+list);
System.out.println("===============================使用工具类复制===============================");
Person person = new Person();
PropertyUtil.setProperty(person, "name", "长草颜团子");
PropertyUtil.setProperty(person, "age", 18);
Student stu = new Student();
PropertyUtil.setProperty(stu, "score", 98);
System.out.println(person.toString());
System.out.println(stu.getScore());
}
@Test
public void test2() throws InstantiationException, IllegalAccessException, NoSuchMethodException,
NoSuchFieldException, InvocationTargetException, IOException {
System.out.println("************************反射获取类的实例,并操作************************");
demo01();
}
}
Copy the code3. Schematic diagram of project structure
