前端指定返回字段解决方案

冷不防 2021-09-21 10:06 442阅读 0赞

### 一，业务场景 ###

个别场景中需要前端指定返回字段解决方案。必须一些可以编辑显示列的table，在这讨论几种实现方式。思路如下：

1，后端数据全返回，前端控制显示与否，缺点是增加数据库查询压力（都查出来了），增加流量传输。

2，数据库查询所有字段业务层序列化的时候指定序列化的字段，缺点就是增加数据库查询压力。

3，数据库动态查询，缺点是安全性健壮性不好把控（不可使用预先编译且有sql注入风险）。

仁者见仁智者见智，有没有更优秀，更优雅的方法欢迎谈论。

### 二，实现 ###

第一种不用说，后端和往常一样，该怎么样还怎么样。

下面说后两种。

JSON序列化之指定序列化字段（fastjson,gson,jackson）

**1，jackson**

import com.fasterxml.jackson.annotation.JsonFilter;
    import com.fasterxml.jackson.core.JsonProcessingException;
    import com.fasterxml.jackson.databind.ObjectMapper;
    import com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter;
    import com.fasterxml.jackson.databind.ser.impl.SimpleFilterProvider;
    import org.springframework.util.StringUtils;
    
    /**
     * jackson自定义JSON返回字段
     *
     * @author Mr_Lee
     * @date 2020-08-13 08:35
     */
    public class JackSonFilter {
    
        private static final String INCLUDE = "JSON_INCLUDE";
        private static final String EXCEPT = "JSON_EXCEPT";
    
        @JsonFilter(INCLUDE)
        private interface MyJsonInclude {
        }
    
        @JsonFilter(EXCEPT)
        private interface MyJsonExcept {
        }
    
        /**
         * 引入字段
         */
        public static String mapperInclude(Object bean, String include) throws JsonProcessingException {
    
            ObjectMapper mapper = new ObjectMapper();
    
            if (StringUtils.hasText(include)) {
                mapper.setFilterProvider(new SimpleFilterProvider().addFilter(INCLUDE,
                        SimpleBeanPropertyFilter.filterOutAllExcept(include.split(","))));
    
                mapper.addMixIn(bean.getClass(), MyJsonInclude.class);
            }
    
            return mapper.writeValueAsString(bean);
        }
    
        /**
         * 排除字段
         */
        public static String mapperExcept(Object bean, String except) throws JsonProcessingException {
    
            ObjectMapper mapper = new ObjectMapper();
    
            if (StringUtils.hasText(except)) {
                mapper.setFilterProvider(new SimpleFilterProvider().addFilter(EXCEPT,
                        SimpleBeanPropertyFilter.serializeAllExcept(except.split(","))));
    
                mapper.addMixIn(bean.getClass(), MyJsonExcept.class);
            }
    
            return mapper.writeValueAsString(bean);
        }
    }

**2，gson**

import com.google.gson.ExclusionStrategy;
    import com.google.gson.FieldAttributes;
    import com.google.gson.Gson;
    import com.google.gson.GsonBuilder;
    import org.springframework.util.StringUtils;
    
    import java.util.Arrays;
    
    /**
     * Gson自定义JSON返回字段
     *
     * @author Mr_Lee
     * @date 2020-08-13 10:04
     */
    public class GsonFilter {
    
        /**
         * 引入字段
         */
        public static String toIncludeJson(Object bean, String include) {
    
            ExclusionStrategy myExclusionStrategy = new ExclusionStrategy() {
                @Override
                public boolean shouldSkipField(FieldAttributes fa) {
    
                    if (StringUtils.hasText(include)) {
                        return !Arrays.asList(include.split(",")).contains(fa.getName());
                    }
    
                    return true;
                }
    
                @Override
                public boolean shouldSkipClass(Class<?> clazz) {
                    return false;
                }
            };
    
            Gson gson = new GsonBuilder().setExclusionStrategies(myExclusionStrategy).create();
            return gson.toJson(bean);
        }
    
        /**
         * 排除字段
         */
        public static String toExceptJson(Object bean, String except) {
    
            ExclusionStrategy myExclusionStrategy = new ExclusionStrategy() {
                @Override
                public boolean shouldSkipField(FieldAttributes fa) {
    
                    if (StringUtils.hasText(except)) {
                        return Arrays.asList(except.split(",")).contains(fa.getName());
                    }
    
                    return false;
                }
    
                @Override
                public boolean shouldSkipClass(Class<?> clazz) {
                    return false;
                }
            };
    
            Gson gson = new GsonBuilder().setExclusionStrategies(myExclusionStrategy).create();
            return gson.toJson(bean);
        }
    }

**3，fastjson**

import com.alibaba.fastjson.JSONObject;
    import com.alibaba.fastjson.serializer.SimplePropertyPreFilter;
    import org.springframework.util.StringUtils;
    
    import java.util.Arrays;
    
    /**
     * FastJson自定义JSON返回字段
     *
     * @author Mr_Lee
     * @date 2020-08-13 09:57
     */
    public class FastJsonFilter {
    
        /**
         * 引入字段
         */
        public static String toIncludeJSONString(Object bean, String include) {
            SimplePropertyPreFilter filter = new SimplePropertyPreFilter();
    
            if (StringUtils.hasText(include)) {
                filter.getIncludes().addAll(Arrays.asList(include.split(",")));
            }
    
            return JSONObject.toJSONString(bean, filter);
        }
    
        /**
         * 排除字段
         */
        public static String toExceptJSONString(Object bean, String except) {
            SimplePropertyPreFilter filter = new SimplePropertyPreFilter();
    
            if (StringUtils.hasText(except)) {
                filter.getExcludes().addAll(Arrays.asList(except.split(",")));
            }
    
            return JSONObject.toJSONString(bean, filter);
        }
    }

测试

import com.fasterxml.jackson.core.JsonProcessingException;
    
    /**
     * @author Mr_Lee
     * @date 2020-08-13 08:37
     */
    public class TestCase {
    
        public static void main(String[] args) throws JsonProcessingException {
    
            User user = new User(1, "lwc", "123456", true, "liwc0329@gmail.com");
    
            String jackSonString1 = JackSonFilter.mapperInclude(user, "id,userName");
            String jackSonString2 = JackSonFilter.mapperExcept(user, "id");
            System.out.println(jackSonString1);
            System.out.println(jackSonString2);
    
            System.out.println("---------------------------------------------");
    
            String fastJsonString1 = FastJsonFilter.toIncludeJSONString(user, "id,userName");
            String fastJsonString2 = FastJsonFilter.toExceptJSONString(user, "id");
            System.out.println(fastJsonString1);
            System.out.println(fastJsonString2);
    
    
            System.out.println("---------------------------------------------");
    
            String gsonString1 = GsonFilter.toIncludeJson(user, "id,userName");
            String gsonString2 = GsonFilter.toExceptJson(user, "id");
            System.out.println(gsonString1);
            System.out.println(gsonString2);
        }
    
    
    }

> \{"id":1,"userName":"lwc"\}  
> \{"userName":"lwc","passWord":"123456","status":true,"email":"liwc0329@gmail.com"\}  
> \---------------------------------------------  
> \{"id":1,"userName":"lwc"\}  
> \{"email":"liwc0329@gmail.com","passWord":"123456","status":true,"userName":"lwc"\}  
> \---------------------------------------------  
> \{"id":1,"userName":"lwc"\}  
> \{"userName":"lwc","passWord":"123456","status":true,"email":"liwc0329@gmail.com"\}

通过上面的方法可以实现方法二。

方法三呢？

可用MyBatis的动态SQL进行数据返回；故可在业务层将指定返回的列传入数据层，利用foreach标签进行遍历返回数据。

1.请求参数

@Data
    public class QueryDTO {
    
        /**
         * 返回值
         */
        private Set<String> targetFields;
    }

2.mapper接口

/**
         * 查询数据
         * @param record
         * @return
         */
        List<ResourceTotal> query(QueryDTO record);

3.mapper.xml实现

<sql id="Base_Result_Column">
        resourceId, platformCount, createUserId
      </sql>
    
      <select id="query" parameterType="cn.example.module.data.test.QueryDTO" resultMap="BaseResultMap">
        select
        <foreach collection="targetFields" item="item" separator=",">
          ${item}
        </foreach>
        ,
        <include refid="Base_Result_Column"/>
        from resource_total
        where 1 = 1
      </select>

4.注意事项  
a.使用动态返回字段时，不可使用预先编译，故foreach中使用‘$’符号，而不使用‘\#’；  
b.foreach标签后若还有其他固定字段返回，记得用逗号‘,’分隔。