JavaSE-高级特性

一、单元测试

使用Junit框架

二、反射

反射可以破坏封装性，得到一个类的所有成分，最重要的途径是用来参与Java框架制作。
获取Class对象的三种方式

• Class c1 = 类名.class
• 调用Class提供方法: public static Class forName(String package);
• Object提供的方法: public Class getClass(); Class c3 = 对象.getClass();

反射案例

需求：对于任意对象，将对象的字段名和对应的值保存到文件中去
假设我们有Teacher类和Student类，那么代码如下

language-java

public class Demo01 {
   
    private String dirPath = "src/main/resources/P13/";

    @Test
    public void test01() {
   
        Student s1 = new Student("淇",22,'女',167.56,"swim");
        Teacher t1 = new Teacher("柳",5433.2);

        work(s1, dirPath+"s.txt");
        work(t1, dirPath+"t.txt");
    }

    public void work(Object object, String filePath) {
   
        //1.create fileIO
        try (
//                FileWriter fileWriter = new FileWriter(filePath);
                PrintWriter printWriter = new PrintWriter(filePath);
        ) {
   
            //2.get Object fields info
            Class c = object.getClass();
            Field[] declaredFields = c.getDeclaredFields();
            printWriter.println("--------"+c.getSimpleName()+"--------");
            for (Field f : declaredFields) {
   
                f.setAccessible(true);
                printWriter.println(f.getName()+" --> "+f.get(object));
            }
        } catch (Exception e) {
   
            throw new RuntimeException(e);
        }
    }
}

三、注解

我的注解一如下

language-java

public @interface MyAnnotation {
   
    String aaa();
    boolean bbb() default true;
    String[] ccc();
}

注解二如下

language-java

public @interface MyAnnotation2 {
   
    String value();
}

注解使用如下

language-java

package org.kmo.d08_Annotation.Test01;

import org.junit.Test;

@MyAnnotation(aaa="牛魔王", ccc={
   "Python","Java"})
public class MyTest01 {
   
    @MyAnnotation(aaa="铁山",bbb=false,ccc={
   "C++","C"})
    public void test1(){
   
    }

    @MyAnnotation2("孙悟空")
    public void test2(){
   
    }
}

解析注解案例

需求：
定义注解MyTest4。
定义一个Demo类,在类中定义一个test1方法，并在该类和其方法上使用MyTest4注解。
定义AnnotationTest3测试类,解析Demo类中的全部注解。

这是一个注解

language-java

@Target({
   ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyTest4 {
   
    String value();
    double aaa() default 100;
    String[] bbb();
}

这是Demo类

language-java

@MyTest4(value = "vv",aaa = 99.9, bbb={
   "b","bb","bbb"})
public class Demo {
   

    @MyTest4(value = "我是至尊宝",aaa = 100.9, bbb = {
   "小淇","爱你"})
    public void test01(){
   

    }
}

这是解析类，解析Demo类上的注解以及Demo类方法的注解

language-java

public class AnnotationTest3 {
   

    @Test
    public void test01(){
   
        Class c = Demo.class;
        if (c.isAnnotationPresent(MyTest4.class)){
   
            MyTest4 myTest4 = (MyTest4) c.getDeclaredAnnotation(MyTest4.class);
            System.out.println(myTest4.value());
            System.out.println(myTest4.aaa());
            System.out.println(Arrays.toString(myTest4.bbb()));
        }
    }
    @Test
    public void test02() throws Exception {
   
        Class c = Demo.class;
        Method method = c.getDeclaredMethod("test01");
        if (method.isAnnotationPresent(MyTest4.class)){
   
            MyTest4 myTest4 = (MyTest4) method.getDeclaredAnnotation(MyTest4.class);
            System.out.println(myTest4.value());
            System.out.println(myTest4.aaa());
            System.out.println(Arrays.toString(myTest4.bbb()));
        }
    }
}

注解案例-简易Junit

这是一个注解

language-java

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyTest {
   

}

这是运行代码

language-java

public class Demo {
   
    @MyTest()
    public void test01(){
   
        System.out.println("===Test01====");
    }

    public void test02(){
   
        System.out.println("===Test02====");
    }

    @MyTest
    public void test03(){
   
        System.out.println("===Test03====");
    }
    public void test04(){
   
        System.out.println("===Test04====");
    }

    public static void main(String[] args) throws Exception {
   
        Demo demo = new Demo();
        Class c = Demo.class;
        Method[] methods = c.getDeclaredMethods();
        for (Method method : methods) {
   
            if (method.isAnnotationPresent(MyTest.class)){
   
                 method.invoke(demo);
            }
        }
    }
}

四、动态代理

相当于把相同的地方集合到一起了，只要写一遍，且灵活。

动态代理案例

需求：对一个类的所有方法前后都加上计时，当类的方法被调用时，输出时间。

一个UserService接口

language-java

public interface UserService {
   
    void login(String loginName, String password) throws Exception;
    void deleteUsers() throws Exception;
    String[] selectUsers() throws Exception;
}

UserServicelmpl实现类

language-java

public class UserServiceImpl implements UserService {
   
    @Override
    public void login(String loginName, String passWord) throws Exception {
   
        if ("admin".equals(loginName) && "123456".equals(passWord)) {
   
            System.out.println("您登录成功，欢迎光临本系统~");
        } else {
   
            System.out.println("您登录失败，用户名或密码错误~");
        }
        Thread.sleep(1000);
    }

    @Override
    public void deleteUsers() throws Exception {
   
        System.out.println("成功删除了1万个用户~");
        Thread.sleep(1500);
    }

    @Override
    public String[] selectUsers() throws Exception {
   
        System.out.println("查询出3个用户");
        String[] names = {
   "张全蛋","李二狗","牛爱花"};
        Thread.sleep(500);
        return names;
    }
}

ProxyUtil代理类

language-java

public class ProxyUtil {
   
    public static UserService createProxy(UserService userService){
   
        UserService userServiceProxy = (UserService) Proxy.newProxyInstance(
                ProxyUtil.class.getClassLoader(),
                new Class[]{
   UserService.class},
                new InvocationHandler() {
   
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
   
                        if (method.getName().equals("login") || method.getName().equals("deleteUsers") || method.getName().equals("selectUsers")){
   
                            long startTime = System.currentTimeMillis();
                            Object res = method.invoke(userService, args);
                            long endTime = System.currentTimeMillis();
                            System.out.println(method.getName()+"方法执行耗时: " + (endTime - startTime) / 1000.0 + "s");
                            return res;
                        }else {
   
                            Object res = method.invoke(userService, args);
                            return res;
                        }
                    }
                }
        );

        return userServiceProxy;
    }
}

在这个代理中，被代理的类传入，Proxy.newProxyInstance中重写的invoke方法里，就是在重写被代理类的所有方法，可以理解为在调用（被代理的）类的方法时，其实是在调用这里的invoke。如果不想做更改，直接执行method.invoke就行。

运行代码

language-java

public class Tests {
   
    public static void main(String[] args) throws Exception {
   
//        UserService userService = new UserServiceImpl();
        UserService userService = ProxyUtil.createProxy(new UserServiceImpl());

        userService.login("admin","123456");
        System.out.println("--------------------");
        userService.deleteUsers();
        System.out.println("--------------------");
        String[] strings = userService.selectUsers();
        System.out.println(Arrays.toString(strings));
        System.out.println("--------------------");

    }
}