022.自定义注解

缺乏、安全感 2021-10-06 15:40 227阅读 0赞

注解是Jdk1.5新增新技术。很多框架为了简化代码，都会提供有些注解。  
可以理解为插件，是代码级别的插件，在类的方法上写：@XXX，就是在代码上插入了一个插件。  
注解不会也不能影响代码的实际逻辑，仅仅起到辅助性的作用。

--------------------

#### 定义 ####

Java文件中叫做Annotation，用@interface表示。

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#### 元注解 ####

@interface上面按需要注解上一些东西，  
包括 **@Retention**、**@Target**、**@Document**、**@Inherited**四种。

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#### 注解的保留策略 ####

// 注解仅存在于源码中，在class字节码文件中不包含
    @Retention(RetentionPolicy.SOURCE)   
    // 默认的保留策略，注解会在class字节码文件中存在，但运行时无法获得
    @Retention(RetentionPolicy.CLASS)     
    // 注解会在class字节码文件中存在，在运行时可以通过反射获取到
    @Retention(RetentionPolicy.RUNTIME)

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#### 注解的作用目标 ####

// 接口、类、枚举、注解
    @Target(ElementType.TYPE)                      
    // 字段、枚举的常量
    @Target(ElementType.FIELD)                     
    // 方法
    @Target(ElementType.METHOD)                 
     // 方法参数
    @Target(ElementType.PARAMETER)           
    // 构造函数
    @Target(ElementType.CONSTRUCTOR)       
    // 局部变量
    @Target(ElementType.LOCAL_VARIABLE)   
     // 注解
    @Target(ElementType.ANNOTATION_TYPE)
    // 包
    @Target(ElementType.PACKAGE)

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#### 注解包含在javadoc中 ####

@Documented

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#### 注解可以被继承 ####

@Inherited

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#### 通过注解进行校验 ####

##### demo1 #####

package cn.qbz.thread.day1121;
    
    import java.lang.annotation.*;
    
    @Documented
    @Inherited
    @Target({ ElementType.FIELD, ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface UserAnnotation { 
        int min() default 0;
    
        int max() default 120;
    
        boolean isNotNull() default true;
    }

package cn.qbz.thread.day1121;
    
    public class User { 
        @UserAnnotation(isNotNull = true)
        private String name;
        @UserAnnotation(min = 18, max = 50)
        private Integer age;
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public Integer getAge() { 
            return age;
        }
    
        public void setAge(Integer age) { 
            this.age = age;
        }
    }

package cn.qbz.thread.day1121;
    
    import java.lang.reflect.Field;
    
    public class UserCheck { 
    
        public static boolean check(User user) throws Exception { 
    
            if (user == null) { 
                System.out.println("user is null.");
                return false;
            }
    
            Field[] fields = User.class.getDeclaredFields();
            for (Field field : fields) { 
                field.setAccessible(true);
                UserAnnotation userAnnotation = field.getAnnotation(UserAnnotation.class);
                String name = field.getName();
                Object value = field.get(user);
                int min = userAnnotation.min();
                int max = userAnnotation.max();
                boolean isNull = userAnnotation.isNotNull();
    
                if (isNull) { 
                    if (value == null) { 
                        throw new Exception(name + " is null.");
                    }
                    int length = value.toString().length();
                    if (length < min) { 
                        throw new Exception(name + " length min is " + min);
                    }
                    if (length > max) { 
                        throw new Exception(name + " length max is " + max);
                    }
                }
            }
            return true;
        }
    }

package cn.qbz.thread.day1121;
    
    public class AnnotationTest { 
        public static void main(String[] args) throws Exception { 
            User user = new User();
            user.setAge(3);
            user.setName("sdfaf");
    
            UserCheck.check(user);
        }
    
    }

##### demo2 #####

<dependency>
                <groupId>javax.validation</groupId>
                <artifactId>validation-api</artifactId>
                <version>1.1.0.Final</version>
            </dependency>

package com.antzb.chaos.annotations;
    
    import com.alibaba.fastjson.JSONArray;
    import com.alibaba.fastjson.JSONObject;
    import com.antzb.chaos.constant.ConstantKey;
    import com.antzb.chaos.utils.CommonUtil;
    import org.springframework.util.StringUtils;
    
    import javax.validation.Constraint;
    import javax.validation.ConstraintValidator;
    import javax.validation.ConstraintValidatorContext;
    import javax.validation.Payload;
    import java.lang.annotation.*;
    import java.util.ArrayList;
    import java.util.List;
    
    /** * @Author: qubianzhong * @Date: 18-4-12 下午1:38 */
    @Documented
    @Target({ ElementType.PARAMETER, ElementType.FIELD})
    @Retention(RetentionPolicy.RUNTIME)
    @Constraint(validatedBy = ProjectUpdateTemplate.OrderByValidator.class)
    public @interface ProjectUpdateTemplate { 
    
        String message() default "[任务步骤格式有误！]";
    
        Class<?>[] groups() default { };
    
        Class<? extends Payload>[] payload() default { };
    
        class OrderByValidator implements ConstraintValidator<ProjectUpdateTemplate, JSONObject> { 
            @Override
            public void initialize(ProjectUpdateTemplate projectUpdateTemplate) { 
            }
    
            @Override
            public boolean isValid(JSONObject template, ConstraintValidatorContext context) { 
                context.disableDefaultConstraintViolation();
                boolean isRight = true;
                String errorMessage = "";
                if (template != null && template.size() > 0) { 
                    for (String key : template.keySet()) { 
                        JSONObject element = template.getJSONObject(key);
                        if (element == null) { 
                            isRight = false;
                            errorMessage = "任务步骤序号异常！必须为:1,2,3,4的字符串.";
                            break;
                        }
                    }
                } else { 
                    isRight = false;
                    errorMessage = "任务步骤不能为空";
                }
                context.buildConstraintViolationWithTemplate(errorMessage).addConstraintViolation();
                return isRight;
            }
        }
    }

public class ProjectUpdateTemplateReq { 
        @NotNull
        private Integer projectInfoId;
        @ProjectUpdateTemplate
        private JSONObject stepTemplate;
    
        public Integer getProjectInfoId() { 
            return projectInfoId;
        }
    
        public void setProjectInfoId(Integer projectInfoId) { 
            this.projectInfoId = projectInfoId;
        }
    
        public JSONObject getStepTemplate() { 
            return stepTemplate;
        }
    
        public void setStepTemplate(JSONObject stepTemplate) { 
            this.stepTemplate = stepTemplate;
        }
    }

@PostMapping
        public ResultMessage updateProjectOfTemplate(@Valid @RequestBody ProjectUpdateTemplateReq projectUpdateTemplateReq) { 
         
         }

##### demo3 #####

package com.rongyi.smart.web.checker.annotation;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    @Target(ElementType.METHOD)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface CheckLogin { 
    }

package com.antzb.chaos.www.aspect;
    
    import com.antzb.chaos.annotations.CheckLogin;
    import com.antzb.chaos.constant.ConstantKey;
    import com.antzb.chaos.www.util.JwtTokenUtil;
    import io.jsonwebtoken.Claims;
    import org.aspectj.lang.JoinPoint;
    import org.aspectj.lang.annotation.After;
    import org.aspectj.lang.annotation.Aspect;
    import org.aspectj.lang.annotation.Before;
    import org.aspectj.lang.annotation.Pointcut;
    import org.springframework.stereotype.Component;
    import org.springframework.web.context.request.RequestContextHolder;
    import org.springframework.web.context.request.ServletRequestAttributes;
    
    import javax.servlet.http.HttpServletRequest;
    import java.sql.Timestamp;
    
    /** * @Author: qubianzhong * @Date: 18-5-4 上午10:01 */
    @Component
    @Aspect
    public class CheckLoginAspect { 
        @Pointcut("@annotation(checkLogin)")
        public void checkLoginPointCut(CheckLogin checkLogin) { 
        }
    
        @Before("checkLoginPointCut(checkLogin)")
        public void doBefore(JoinPoint joinPoint, CheckLogin checkLogin) { 
            String message = "请扫码登录后重新访问!";
            ServletRequestAttributes sra = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
            HttpServletRequest request = sra.getRequest();
    
            request.setAttribute(ConstantKey.HTTPSERVLETREQUEST_ATTRIBUTES_CHECKLOGIN, true);
    
            String token = request.getHeader(ConstantKey.JWT_HEADER_KEY);
            if (token == null) { 
                throw new SecurityException(message);
            }
            Claims claims = JwtTokenUtil.getClaimsFromToken(token.replace(ConstantKey.JWT_TOKENHEAD_KEY, ""));
            if (claims == null) { 
                throw new SecurityException(message);
            }
            Object userName = claims.get(JwtTokenUtil.CLAIM_KEY_USERNAME);
            Object userId = claims.get(JwtTokenUtil.CLAIM_KEY_USERID);
    
            Timestamp expirationTime = new Timestamp(claims.getExpiration().getTime());
            if (userId == null
                    || userName == null
                    || expirationTime == null
                    || expirationTime.before(new Timestamp(System.currentTimeMillis()))) { 
                throw new SecurityException(message);
            }
        }
    
        @After("checkLoginPointCut(checkLogin)")
        public void doAfter(CheckLogin checkLogin) { 
        }
    }

@GetMapping("/task/list")
        @CheckLogin
        public ResultMessage queryProjectTaskList() { 
            ResultMessage resultMessage = new ResultMessage();
            //......
            return resultMessage;
        }