Mybatis之插件开发之下划线转驼峰形式插件

墨蓝 2023-07-05 13:22 44阅读 0赞

背景：有些人在使用Mybatis时，为了方便扩展而使用Map类型的返回值。使用Map作为返回值时，Map中的键值就是查询结果中的列名，而列名一般都是大小写字母或者下划线形式，因此和Java使用的驼峰形式不一致，而且由于不同数据库查询出来的大小写也不一致，因此为了保证在使用Map是属性一致，可以对Map类型结果进行特殊处理，即不同格式的列名转换为Java的驼峰形式命名。这种情况下我们可以使用拦截器，通过拦截**ResultSetHander**接口中的**handleResultSets**方法去处理Map类型的结果，拦截器代码如下：

### 1，拦截器类CameHumpInterceptor.class ###

package person.david.ssm.interceptor;
    
    import org.apache.ibatis.executor.resultset.ResultSetHandler;
    import org.apache.ibatis.plugin.*;
    
    import java.sql.Statement;
    import java.util.*;
    
    /**
     * @author David
     * @className CameHumpInterceptor
     * Mybatis Map 类型下划线key转小写驼峰形式
     * @date 2020/2/13 20:40
     */
    @Intercepts(
            @Signature(
                    type = ResultSetHandler.class,
                    method = "handleResultSets",
                    args = {
        Statement.class})
    
    )
    @SuppressWarnings({
        "unchecked","rawtypes"})
    public class CameHumpInterceptor implements Interceptor {
        
        @Override
        public Object intercept(Invocation invocation) throws Throwable {
        
            System.out.println("==================>开始进行拦截...");
            List<Object> list = (List<Object>)invocation.proceed();
            for (Object object : list) {
        
                //如果结果是Map类型，就对Map的key进行转换
                if (object instanceof Map){
        
                    processMap((Map) object);
                }else {
        
                    break;
                }
            }
            return list;
        }
    
        /**
         * 处理map类型
         *
         * @param map
         */
        private void processMap(Map<String,Object> map){
        
            System.out.println("==================>开始处理map类型...");
    
            Set<String> keySet = new HashSet<>(map.keySet());
            for (String key : keySet) {
        
                //以大写开头的字母为小写，如果包含下划线也会处理为驼峰
                //此处只通过简单的两个标识来判断
                if ((key.charAt(0) >= 'A' && key.charAt(0) <= 'Z') || key.indexOf("_") >= 0 ){
        
                    Object value = map.get(key);
                    map.remove(key);
                    map.put(underlineToCamehunp(key),value);
                }
            }
        }
    
    
        /**
         * 将下划线风格转换为驼峰风格
         * @param inputString
         * @return
         */
        public static String underlineToCamehunp(String inputString){
        
            System.out.println("==================>开始进行转换...");
            StringBuilder sb = new StringBuilder();
            boolean nextUppercase = false;
            for (int i = 0; i < inputString.length(); i++) {
        
                char c = inputString.charAt(i);
                if (c == '_') {
        
                    if (sb.length()>0) {
        
                        nextUppercase = true;
                    }
                }else {
        
                    if (nextUppercase) {
        
                        sb.append(Character.toUpperCase(c));
                        nextUppercase = false;
                    }else {
        
                        sb.append(Character.toLowerCase(c));
                    }
                }
            }
    
            return sb.toString();
        }
    
    
        @Override
        public Object plugin(Object target) {
        
            return Plugin.wrap(target,this);
        }
    
        @Override
        public void setProperties(Properties properties) {
        
    
        }
    }

### 2，接口TestMapper.class ###

@CacheNamespace(eviction = FifoCache.class,flushInterval = 60000,size = 512,readWrite = true)
    public interface TestMapper {
        
       
        Map<Object,Object> selectStuById(int id);
    }

### 3，TestMapper.xml文件 ###

<select id="selectStuById" parameterType="int" resultType="map">
            select stu_name, stu_age, stu_gender, stu_hobby
            from t_test
            where id = #{id}
        </select>

### 4，配置文件里配置写好的拦截器插件 ###

<plugins>
            <plugin interceptor="person.david.ssm.interceptor.CameHumpInterceptor"/>
        </plugins>

### 5，测试类测试下划线转驼峰 ###

@Test
        public void test7(){
        
            SqlSession sqlSession = sqlSessionFactory.openSession();
            TestMapper testMapper = sqlSession.getMapper(TestMapper.class);
            Map<Object ,Object> map = testMapper.selectStuById(4);
            for (Map.Entry<Object, Object> entry : map.entrySet()) {
        
                System.out.println(entry.getKey()+"=========>"+entry.getValue());
            }
        }

#### 测试结果 ####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTEzNDMw_size_16_color_FFFFFF_t_70]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTEzNDMw_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200215140600983.PNG?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTEzNDMw,size_16,color_FFFFFF,t_70