第二十三章、反射
补充动态语言和静态语言区别
1、反射机制
1.1java反射机制示意图
1.2、Java反射机制可以完成
1、在运行时判断任意一个对象所属的类
2、在运行时构造（创建）任意一个类的对象
3、在运行时得到任意一个类所具有的成员变量和方法
4、在运行时调用任意一个对象的成员变量和方法
5、生成动态代理
1.2、java反射的优缺点
1.3、反射相关的主要类
2、Class类
2.1、介绍
2.2、Class类的常用方法
2.3、获取Class的实例
1、内容
2、例子
package reflection;
public class Test03 {
public static void main(String [] args) throws ClassNotFoundException {
Persion persion = new Student();
System.out.println("这个人是："+persion.name);
// 方式一通过对象获得
Class c1 = persion.getClass();
System.out.println(c1.hashCode());
// 方式二froname获得
Class c2 = Class.forName("reflection.Student");
System.out.println(c2.hashCode());
// 方式三、通过类名.class获得
Class c3 = Student.class;
System.out.println(c3.hashCode());
// 获取父类类型
Class c4 = c1.getSuperclass();
System.out.println(c4);
// 基本内置类型都会有一个
Class [] c5 =c1.getInterfaces();
System.out.println(c5);
}
}
class Persion{
public String name;
public int age;
}
class Student extends Persion {
public Student() {
this.name = "我是个学生";
}
}
class Teacher extends Persion{
public Teacher() {
this.name ="我是个老师";
}
}2.4、哪些类型可以有Class对象
1、内容
2、例子
Class c1 = Object.class;//类
Class c2 = Comparable.class;//接口
Class c3 = String [].class;//一维数组
Class c4 = int[][].class;//二维数组
Class c5 = Override.class;//注解
Class c6 = ElementType.class;//枚举
Class c7 = Integer.class;//基本数据类型
Class c8 = void.class;//方法
Class c9 = Class.class;//类
System.out.println(c1);
System.out.println(c2);
System.out.println(c3);
System.out.println(c4);
System.out.println(c5);
System.out.println(c6);
System.out.println(c7);
System.out.println(c8);
System.out.println(c9);
//只要元素类型与维度一样，就是同一个class
int [] a = new int [10];
int [] b = new int [10000];
System.out.println(a.getClass().hashCode());
System.out.println(b.getClass().hashCode());
结果
/**
class java.lang.Object
interface java.lang.Comparable
class [Ljava.lang.String;
class [[I
interface java.lang.Override
class java.lang.annotation.ElementType
class java.lang.Integer
void
class java.lang.Class
366712642
366712642 *//2.5、java中内存分析
1、图解
2、类加载的过程
3、类的加载与ClassLoaderd的理解
4、什么时候会发生类的初始化
2.6、类加载器
1、作用
2、类加载器的个数
2.7、获取运行时类的完整形式
package reflection;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class Test08 {
public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, NoSuchMethodException {
// 获取类的名字
Class c1 = Class.forName("reflection.User");
System.out.println(c1.getName());
System.out.println(c1.getSimpleName());
// 获取类的属性
Field[] fields = c1.getFields();//只能找到公共的类public
fields = c1.getDeclaredFields();//找到全部的属性
for (Field field:fields) {
System.out.println(field);
}
// 获取指定属性的值
Field name = c1.getDeclaredField("name");
System.out.println(name);
// 获取类的方法
System.out.println("================");
Method [] methods = c1.getMethods();//获取所有类的方法
for (Method method : methods) {
System.out.println("正常的："+method);
}
methods = c1.getDeclaredMethods();//获得本类的所有方法
for (Method method : methods) {
System.out.println("DeclaredMethods："+method);
}
// 获取指定属性的值
Field name1 = c1.getDeclaredField("name");
System.out.println(name);
// 获取类的指定方法
System.out.println("================");
Method getName = c1.getMethod("getName",null);
Method setName = c1.getMethod("setName", String.class);
System.out.println(getName);
System.out.println(setName);
// 获取全部构造器
System.out.println("================");
Constructor[] constructors = c1.getConstructors();
for (Constructor constructor : constructors) {
System.out.println(constructor);
}
constructors = c1.getDeclaredConstructors();
for (Constructor constructor : constructors) {
System.out.println("区分"+constructor);
}
// 获取指定的构造器
Constructor declaredConstructor = c1.getDeclaredConstructor(String.class,int.class,int.class);
System.out.println("指定："+declaredConstructor);
}
}
/**
结果
"C:\Program Files\Java\jdk1.8.0_351\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2021.2\lib\idea_rt.jar=1904:C:\Program Files\JetBrains\IntelliJ IDEA 2021.2\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_351\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_351\jre\lib\rt.jar;C:\Users\qt\IdeaProjects\chapter21\out\production\chapter21" reflection.Test08
reflection.User
User
private java.lang.String reflection.User.name
private int reflection.User.id
private int reflection.User.age
private java.lang.String reflection.User.name
================
正常的：public java.lang.String reflection.User.getName()
正常的：public int reflection.User.getId()
正常的：public void reflection.User.setName(java.lang.String)
正常的：public void reflection.User.setId(int)
正常的：public void reflection.User.setAge(int)
正常的：public int reflection.User.getAge()
正常的：public final void java.lang.Object.wait() throws java.lang.InterruptedException
正常的：public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
正常的：public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
正常的：public boolean java.lang.Object.equals(java.lang.Object)
正常的：public java.lang.String java.lang.Object.toString()
正常的：public native int java.lang.Object.hashCode()
正常的：public final native java.lang.Class java.lang.Object.getClass()
正常的：public final native void java.lang.Object.notify()
正常的：public final native void java.lang.Object.notifyAll()
DeclaredMethods：public java.lang.String reflection.User.getName()
DeclaredMethods：public int reflection.User.getId()
DeclaredMethods：public void reflection.User.setName(java.lang.String)
DeclaredMethods：public void reflection.User.setId(int)
DeclaredMethods：public void reflection.User.setAge(int)
DeclaredMethods：public int reflection.User.getAge()
private java.lang.String reflection.User.name
================
public java.lang.String reflection.User.getName()
public void reflection.User.setName(java.lang.String)
================
public reflection.User(java.lang.String,int,int)
区分public reflection.User(java.lang.String,int,int)
指定：public reflection.User(java.lang.String,int,int)
Process finished with exit code 0
*//3、class应用
3.1、有了class有啥用
1、作用
3.2、调用指定的方法
3.3、setAccessible：安全访问机制
3.4、反射实例（基础操作）
package reflection;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class Test09 {
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException, NoSuchFieldException {
// 通过构造器创建对象
Class c1 = Class.forName("reflection.User");
Constructor constructor = c1.getDeclaredConstructor(String.class,int.class,int.class);
User user2 = (User) constructor.newInstance("秦涛",001,18 );
System.out.println(user2);
// 通过反射调用普通方法
User user3 = (User) c1.newInstance();
// 通过反射获取一个方法
Method setName = c1.getDeclaredMethod("setName",String.class);
// invoke：是调用、激活的意思
setName.invoke(user3,"秦涛");
System.out.println(user3.getName());
System.out.println("99999999999999999999999999999999999999999999999999999999");
// 通过反射操作属性
User user4 = (User) c1.newInstance();
Field name = c1.getDeclaredField("name");
name.setAccessible(true);
name.set(user4,"秦涛111111");
System.out.println(user4.getName());
//
}
}3.5、反射性能对比
1、排行
1、普通方法>反射调用(关闭安全检测)>反射调用
2、例子
package reflection;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class Test10 {
// 普通调用测试时间
public static void test01(){
User user = new User();
long startTime = System.currentTimeMillis();
for(int i =0;i<1000000000;i++){
user.getName();
}
long endTime = System.currentTimeMillis();
System.out.println("普通方法调用跑了："+(endTime-startTime)+"ms");
}
// 反射进行方法调用测试时间
public static void test02() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
User user = new User();
Class c1 = user.getClass();
Method getName = c1.getDeclaredMethod("getName",null);
long startTime = System.currentTimeMillis();
for(int i =0;i<1000000000;i++){
getName.invoke(user,null);
}
long endTime = System.currentTimeMillis();
System.out.println("反射方法调用对象跑了："+(endTime-startTime)+"ms");
}
//反射关闭安全检测进行测试时间
public static void test03() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
User user = new User();
Class c1 = user.getClass();
Method getName = c1.getDeclaredMethod("getName",null);
getName.setAccessible(true);
long startTime = System.currentTimeMillis();
for(int i =0;i<1000000000;i++){
getName.invoke(user,null);
}
long endTime = System.currentTimeMillis();
System.out.println("反射关闭安全检测调用对象跑了："+(endTime-startTime)+"ms");
}
public static void main(String[] args) throws InvocationTargetException, NoSuchMethodException, IllegalAccessException {
test01();
test02();
test03();
}
}3.6、反射操作泛型
1、作用、介绍
2、例子
package reflection;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Map;
public class Test11 {
public void test01(Map<String, User> map , List<User> list){
System.out.println("test01");
}
public Map<String,User> test02(){
System.out.println("test02");
return null;
}
public static void main(String[] args) throws NoSuchMethodException {
Method method = Test11.class.getMethod("test01", Map.class,List.class);
Type[] genericParameterTypes = method.getGenericParameterTypes();
for (Type genericParameterType : genericParameterTypes) {
System.out.println("**:"+genericParameterType);
if(genericParameterType instanceof ParameterizedType){ //进行判断genericParameterType是否为一个参数化类型
Type[] autualTypeArguments = ((ParameterizedType)genericParameterType).getActualTypeArguments();//如果是，进行强转，调用getActualTypeArguments（）方法获得真是获得真是的参数类型
for (Type autualTypeArgument : autualTypeArguments) {
System.out.println(autualTypeArgument);
}
}
}
method = Test11.class.getMethod("test02",null);
Type[] genericParameterType1 = method.getGenericParameterTypes();
for (Type genericParameterType : genericParameterType1) {
System.out.println("**:"+genericParameterType);
if(genericParameterType instanceof ParameterizedType){ //进行判断genericParameterType是否为一个参数化类型
Type[] autualTypeArguments = ((ParameterizedType)genericParameterType).getActualTypeArguments();//如果是，进行强转，调用getActualTypeArguments（）方法获得真是获得真是的参数类型
for (Type autualTypeArgument : autualTypeArguments) {
System.out.println(autualTypeArgument);
}
}
}
}
}
/**
结果
**:java.util.Map<java.lang.String, reflection.User>
class java.lang.String
class reflection.User
**:java.util.List<reflection.User>
class reflection.User
Process finished with exit code 03.7、练习ORM
1、内容
2、例子
package reflection;
import com.sun.istack.internal.Interned;
import java.lang.annotation.*;
import java.lang.reflect.Field;
/**
*
* 反射操作注解
*/
public class Test12 {
public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
Class c1 = Class.forName("reflection.Student2");
// 通过反射获得注解
Annotation[] annotations = c1.getAnnotations();
for (Annotation annotation : annotations) {
System.out.println(annotation);
}
// 获取注解的value的值
Tabletao tabletao = (Tabletao) c1.getAnnotation(Tabletao.class);
String value = tabletao.value();
System.out.println(value);
// 获取类指定的注解
Field f = c1.getDeclaredField("age");
Filetao annotation = f.getAnnotation(Filetao.class);
System.out.println(annotation.colunName());
System.out.println(annotation.type());
System.out.println(annotation.length());
}
}
@Tabletao("db_student")
class Student2{
@Filetao(colunName = "db_id",type = "int",length =10)
private int id;
@Filetao(colunName = "db_age",type = "int",length =8)
private int age;
@Filetao(colunName = "db_name",type = "int",length =5)
private String name;
public Student2() {
}
public Student2(int id, int age, String name) {
this.id = id;
this.age = age;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Student2{" +
"id=" + id +
", age=" + age +
", name='" + name + '\'' +
'}';
}
}
//类名的注解
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@interface Tabletao{
String value();
}
//属性的注解
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@interface Filetao{
String colunName();
String type();
int length();
}