Spring Boot AOP + custom annotations + reflection demo

Example: field userId, want to display userName in the page list

Custom annotations

• Introduction to Java annotations Retention, Documented, and Target

• The code shown

  • @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface UserName {
    	
    }
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• Place the annotation on the class field

  • pubilc class User {
        
        @UserName
    	private Integer userId;
    }
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AOP

• If you don’t know AOP, search other blogs, and familiarize yourself with AOP, as well as reflection, before eating

• Define section annotations

  • /** ** on the controller method that needs to be replaced@author MLK
     */
    @Target({ElementType.PARAMETER, ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface Conversion {
    }
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• Define the aspect class

  • The code shown

    @Aspect
    @Component
    @Slf4j
    public class ConversionAspect {
    
        // Define Pointcut Pointcut
        @Pointcut("@annotation(com... Conversion)")
        public void excudeService(a) {}@Around("excudeService()")
        public Object doAroundConversion(ProceedingJoinPoint pjp) {
            // Get the data to return
            Object res = pjp.proceed();
            try {
                parseText(res);
            }catch (Exception e){
                e.printStackTrace();
            }
            returnres; }}Copy the code

  • parseText(res); This method handles the data returned by the controller layer to the front-end page. According to the return format of the project, the list data is fetched.

  • The code shown

    private void parseText(Object result){
            try {
                Iterator<Map.Entry<String, Object>> iterator = ((R) result).entrySet().iterator();
                while (iterator.hasNext()){
                    Map.Entry<String, Object> entry = iterator.next();
                    String key = entry.getKey();
                    Object value = entry.getValue();
                  	
                    // Check paging, my paging data is in rows
                    if ("rows".equals(key)){
                        / / paging
                        List<JSONObject> items = new ArrayList<>();
                        ArrayList list = (ArrayList) value;
                        for(Object o : list) { JSONObject jsonObject = jsonValue(o); items.add(jsonObject); } ((R) result).put(key,items); }}Copy the code

  • jsonValue(o); To get the specific list value, reflect -> get the annotation

  • The code shown

    public JSONObject jsonValue(Object record) {
            ObjectMapper mapper = new ObjectMapper();
            String json = "{}";
            try {
                json = mapper.writeValueAsString(record);
            } catch (JsonProcessingException e) {
                log.error("Json parsing failed" + e.getMessage(), e);
            }
        	// The data to be returned
            JSONObject item = JSONObject.parseObject(json);
        	// convert. getAllFields: Gets all attributes of the class, including the parent class
        	for (Field field : Convert.getAllFields(record)) {
                // Check if there is a UserName annotation
                if(field.getAnnotation(UserName.class) ! =null) {
                    // Get the field
                    String fieldName = field.getName();
                    // Get the field value
                    String fileValue = String.valueOf(item.get(fieldName));
                    // The value is not empty. Get userName according to userId
                    String userName = queryUserNameByUserId(userId);
                    item.put("userName", userName); }}return item;
    }
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