自定义注解说明，使用参数注解拿取登录用户信息

Bertha 。 2023-01-08 05:20 116阅读 0赞

一、自定义一个注解

@Documented
    @Target({ElementType.METHOD,ElementType.TYPE,ElementType.FIELD,ElementType.PARAMETER})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Hello {
    
        String value() ;
    
    }

二、获取实体类里属性上的注解值

1、定义一个实体类

@Data
    @ToString
    public class Student {
    
        @Hello(value = "test")
        private String name;
        private int age;
    
    
    }

2、拿值

@RequestMapping(value = "testAnnocationField")
    public void testAnnocationField() {
         Class<Student> studentClass = Student.class;
         try {
                Field name = studentClass.getDeclaredField("name");
                name.setAccessible(true);
                if(name.isAnnotationPresent(Hello.class)){ // 是否有注解
                    Hello annotation = name.getAnnotation(Hello.class);
                    String value = annotation.value();
                    System.out.println(value);
                }
          } catch (NoSuchFieldException e) {
                e.printStackTrace();
          }
    }
    
     执行结果： test

三、获取方法上的注解值

@RequestMapping(value = "testAnnotation1")
    @Hello(value = "test")
    public void testAnnotation1() throws NoSuchMethodException {
        Class<PractiseController> practiseControllerClass = PractiseController.class;
        Method method = practiseControllerClass.getMethod("testAnnotation1");
        if(method.isAnnotationPresent(Hello.class)) { // 判断方法上是否有注解
             Hello annotation = method.getAnnotation(Hello.class);
             System.out.println(annotation.value());
        }
    }
    
    执行结果： test
    备注： PractiseController 为类名

四、动态获得方法上的注解值

1、创建yml文件

server:
      port: 8088
    spring:
      profiles:
        active: dev

2、获得动态值

@RequestMapping(value = "testAnnotation")
    @Hello(value = "${server.port}")
    public void testAnnotation() throws NoSuchMethodException {
        Class<PractiseController> practiseControllerClass = PractiseController.class;
        Method method = practiseControllerClass.getMethod("testAnnotation");
        if(method.isAnnotationPresent(Hello.class)) {
             Hello annotation = method.getAnnotation(Hello.class);
             System.out.println(environment.resolvePlaceholders(annotation.value()));
        }
    }
    
    执行结果： 8088

五、 参数注解，获取登录用户信息较为常用

1、创建登录用户信息处理器，实现解析器 HandlerMethodArgumentResolver 接口

import com.example.zhujie.annotation.LoginUser;
    import com.example.zhujie.entity.SysUser;
    import org.springframework.core.MethodParameter;
    import org.springframework.stereotype.Component;
    import org.springframework.web.bind.support.WebDataBinderFactory;
    import org.springframework.web.context.request.NativeWebRequest;
    import org.springframework.web.method.support.HandlerMethodArgumentResolver;
    import org.springframework.web.method.support.ModelAndViewContainer;
    
    @Component
    public class LoginUserHandlerMethodArgumentResolver implements HandlerMethodArgumentResolver {
    
        // 判断当前用户是否有注解参数 @LoginUser SysUser sysUser
        @Override
        public boolean supportsParameter(MethodParameter parameter) {
            return parameter.getParameterType().isAssignableFrom(SysUser.class) && 
            parameter.hasParameterAnnotation(LoginUser.class);
        }
    
        @Override
        public Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer 
            modelAndViewContainer, NativeWebRequest nativeWebRequest, WebDataBinderFactory             
            webDataBinderFactory) throws Exception {
                // 给注解参数SysUser 赋值，此处作为测试，因此写了死值，实际开发中，可将登录成功后存入session 或者redis中的用户id取出，查询当前登录用户从而赋值
                SysUser sysUser = new SysUser();
                sysUser.setId("ghjklyuiohjkhjk");
                sysUser.setName("testUser");
            return sysUser;
        }
    }

2、创建参数注解@LoginSysUser

@Documented
    @Target({ElementType.PARAMETER})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface LoginUser {
    
        String value()  default  "";
    
    }

3、将自定义参数解析器设置到spring的参数解析器集合中

import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.web.method.support.HandlerMethodArgumentResolver;
    import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
    
    import java.util.List;
    
    @Configuration
    public class LoginUserConfigurer implements WebMvcConfigurer {
    
        @Autowired
        private LoginUserHandlerMethodArgumentResolver loginUserHandlerMethodArgumentResolver;
    
        @Override
        public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
            resolvers.add(loginUserHandlerMethodArgumentResolver);
        }
    }

4、测试

@RequestMapping(value = "/testLoginUser")
    @ResponseBody
    public String getPort(@LoginUser SysUser sysUser){
        System.out.println(sysUser);
       return null;
    }
    
    
    结果： SysUser(name=testUser, id=ghjklyuiohjkhjk)