Java注解与反射各个知识点总结(很全)

@RestController
@RequestMapping("/api")
public class ConsumeController {
    @RequestMapping("/hello/user")
    @ResponseBody
    public User hello() {
        return userService.hello();
    }
}
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@Target(ElementType.TYPE) // 可作用类接口枚举
@Retention(RetentionPolicy.RUNTIME) // 运行时
@Inherited // 可继承
@Documented
public @interface Log1 {
    String info() default "";
}
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@Log1(info = "info")
public class AnnoTest {}
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public static void reflect() {
    // 内置反射
    Class<?> annoClass = null;
    try {
        // 获取对象
        annoClass = Class.forName("com.java.lang.base.annotation.AnnoTest");
        // 判断是否存在注解log1
        boolean isAnnoLog1 = annoClass.isAnnotationPresent(Log1.class);
        Log.info("anno log1 exist: " + isAnnoLog1); // true
        if (isAnnoLog1) {
            // 获取注解
            Log1 annotation = annoClass.getAnnotation(Log1.class);
            Log.info("info ----" + annotation.info()); 
        }
    } catch(Exception e) {
        Log.info(e.getMessage());
    }
}
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@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Log1 {
    String info() default "";
}
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public class AnnoTest {
    @Log1(info="info")
    public String hello(String msg) {
        System.out.println("动态设置 --- " +  msg);
        return "返回值---->" + msg;
    }
}
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public static void reflect() {
    // 内置反射
    Class<?> annoClass = null;
    try {
        // 获取对象
        annoClass = Class.forName("com.java.lang.base.annotation.AnnoTest");
        // 获取方法
        Method[] methods = annoClass.getDeclaredMethods();
        // 方法遍历:
        for (Method declaredMethod : methods) {
            // 判断方法是否存在注解
            boolean isAnnoLog = declaredMethod.isAnnotationPresent(Log1.class);
            if(isAnnoLog) {
                annotation = declaredMethod.getAnnotation(Log1.class);
                // 获取构造器
                Constructor<?> constructor = annoClass.getConstructor();
                // 实例化
                Object obj = constructor.newInstance();
                // 执行方法 - 将注解的数据执行进去
                Log.info(declaredMethod.invoke(obj, annotation.info()));
            }
        }
    } catch(Exception e) {
        Log.info(e.getMessage());
    }
}
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@Target(ElementType.TYPE) // 可作用类接口枚举
@Retention(RetentionPolicy.RUNTIME) // 运行时
@Inherited // 可继承
@Documented
// 继承Log2注解
@Log2
public @interface Log1 {
    // 显示传递 这里可以接收err的属性值
    // 显示专递时需要加上  @AliasFor 去标记, 并且default要一致
    @AliasFor(value="err")
    String info() default "";
    @AliasFor(value="info")
    String err() default "";
    // 隐式传递 - 属性名以Log2的属性名
    @AliasFor(annotation = Log2.class, attribute = "log2")
    String err1() default "";
    @AliasFor(annotation = Log2.class, attribute = "log2")
    String err2() default "";
}
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@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Log2 {
    String log2() default "";
}
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@Log1(err1 = "隐式传递 err1")
public class AnnoTest {
}
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public static void reflect() {
    // 内置反射
    Class<?> annoClass = null;
    try {
        // 获取对象
        annoClass = Class.forName("com.java.lang.base.annotation.AnnoTest");
        // 判断是否存在注解log1
        boolean isAnnoLog1 = annoClass.isAnnotationPresent(Log1.class);
        Log.info("anno log1 exist: " + isAnnoLog1); // true
        Log1 annotation = annoClass.getAnnotation(Log1.class);
        //    Log.info("info ----" + annotation.info()); // info ----显式传递 info
        // aop 版本获取注解
        annotation = AnnotationUtils.getAnnotation(annoClass, Log1.class);
        Log.info("err1 ----" + annotation.err1()); // 隐式传递 err1
        Log.info("err2 ----" + annotation.err2()); // 式传递 err2 - 发现err2 并没有传入属性值 - @Log1(err1 = "隐式传递 err1")
    } catch(Exception e) {
        Log.info(e.getMessage());
    }
    }
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@AliasFor(value="err")
String info() default "";
@AliasFor(value="info")
String err() default "";
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// 隐式传递 - 属性名以Log2的属性名
@AliasFor(annotation = Log2.class, attribute = "log2")
String err1() default "";
@AliasFor(annotation = Log2.class, attribute = "log2")
String err2() default "";
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@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Log3 {
    String hello() default "";
}
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@Aspect
@Component
public class SpringAopMain {
    // 切点
    @Pointcut("@annotation(com.java.lang.base.annotation.Log3)")
    public void aspect() {}
    //配置前置通知,使用在方法aspect()上注册的切入点
    //同时接受JoinPoint切入点对象,可以没有该参数
    @Before("aspect()")
    public void Before() {
        Log.info("before ....");
    }
    // 后置通知
    @After("aspect()")
    public void After(JoinPoint point) {
        Log.info("after ...." + point.toString());
    }
    // 最终通知 - 设定返回值为String对象
    @AfterReturning(pointcut = "aspect()", returning = "res")
    public void AfterReturning(String res) {
        Log.info("----AfterReturning方法开始执行:---"+res);
    }
    //异常通知
    @AfterThrowing(pointcut="aspect()",throwing="e")
    public void AfterThrowing(Throwable e) {
        Log.info("-----AfterThrowing方法开始执行:"+e);
    }
    //@Around注解可以用来在调用一个具体方法前和调用后来完成一些具体的任务。
    // 这里的返回值等于方法的返回值
    @Around("aspect()")
    public Object Around(ProceedingJoinPoint joinPoint) throws Throwable {
        Log.info("方法开始执行");
        Signature signature = joinPoint.getSignature();
        // 获取注解绑定的方法
        Method method = ((MethodSignature)signature).getMethod();
        Log3 annotation = AnnotationUtils.getAnnotation(method, Log3.class);
        Log.info("aop log3 --->" + annotation.hello());
        // 获取入参
        Object[] inputArgs = joinPoint.getArgs();
        // 获取参数名
        String[] argNames = ((MethodSignature) signature).getParameterNames();
        Map<String, Object> paramMap = new HashMap<>();
        for(int i = 0; i < argNames.length; i++) {
            paramMap.put(argNames[i], inputArgs[I]);
        }
        Log.info("入参" + paramMap.toString());
        // 修改入参
        inputArgs[0] = "spring aop args";
        // 执行方法
        Object result = joinPoint.proceed(inputArgs);
        Log.info( "反射结果----->"+ result);
        // 返回结果
        return result;
    }
}
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