sql查询返回值使用map封装多个key和value实例

2024-04-02 19:04:59 464人浏览独家记忆

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摘要

直接上代码，代码是测试过的 1.重写ResultHandler public class MapResultHandler implements ResultHandler {

直接上代码，代码是测试过的

1.重写ResultHandler


public class MapResultHandler implements ResultHandler {
    private final Map mappedResults = new HashMap();
    @Override
    public void handleResult(ResultContext context) {
        @SuppressWarnings("rawtypes")
        Map map = (Map) context.getResultObject();
        mappedResults.put(map.get("key"), map.get("value"));
    }
    public Map getMappedResults() {
        return mappedResults;
    }
}

2.在mapper封装


  <resultMap id="retMap" type="java.util.HashMap">
        <result column="keyName" property="key" javaType="java.lang.String"/>
        <result column="val" property="value" javaType="java.math.BigDecimal"/>
    </resultMap>

例子：


SELECT F_NAME keyName,nvl(sum (F_METADATA_VALUE),0) val from 表名
GROUP BY F_CODE, F_NAME

3.service实现


 @Autowired
    private sqlSessionFactory sqlSessionFactory;
    private static final String mapperPath = "mapper的路径.";      
  Map<String, Object> parameter = new HashMap<>();
  //设置参数
        parameter.put("query", query);
  //mapper的方法名
        String methodName = "selectMedicineSurvey";
        //查询数据使用Map封装
        Map<String, BigDecimal> medicineSurveyMap = getStringBigDecimalMap(mapperPath, parameter, methodName);
    //查询数据使用Map封装
    private Map<String, BigDecimal> getStringBigDecimalMap(String mapperPath, Map<String, Object> parameter, String methodName) {
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        MapResultHandler handler = new MapResultHandler();
        sqlSession.select(mapperPath + methodName, parameter, handler);
       //关流
        sqlSession.close();
         //获取结果
        return (Map<String, BigDecimal>) handler.getMappedResults();
    }


sqlSession.close();

一定要记得数据库关流，不然连接数就会把数据库给卡死

mybatis查询两个字段，返回Map，一个字段作为key，一个字段作为value的实现

1. 问题描述

在使用MyBatis，我们经常会遇到这种情况：SELECT两个字段，需要返回一个Map，其中第一个字段作为key，第二个字段作为value。MyBatis的MapKey虽然很实用，但并不能解决这种场景。这里，就介绍一种使用拦截器来解决这个问题的方案。

2. 解决方案

源码详见：spring-mybatis-test

2.1 注解


package com.adu.spring_test.mybatis.annotations;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.METHOD })
public @interface MapF2F {
    
    boolean isAllowKeyRepeat() default true;
    
    boolean isAllowValueDifferentWithSameKey() default false;
}

2.2 拦截器


package com.adu.spring_test.mybatis.interceptor;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Properties;
import org.apache.commons.lang3.StringUtils;
import org.apache.ibatis.executor.resultset.ResultSetHandler;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.plugin.Intercepts;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.plugin.Plugin;
import org.apache.ibatis.plugin.Signature;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.type.TypeHandler;
import org.apache.ibatis.type.TypeHandlerReGIStry;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.dao.DuplicateKeyException;
import com.adu.spring_test.mybatis.annotations.MapF2F;
import com.adu.spring_test.mybatis.util.ReflectUtil;
import javafx.util.Pair;

@Intercepts(@Signature(method = "handleResultSets", type = ResultSetHandler.class, args = { Statement.class }))
public class MapF2FInterceptor implements Interceptor {
    private Logger logger = LoggerFactory.getLogger(MapF2FInterceptor.class);
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        MetaObject metaStatementHandler = ReflectUtil.getRealTarget(invocation);
        MappedStatement mappedStatement = (MappedStatement) metaStatementHandler.getValue("mappedStatement");
        String className = StringUtils.substringBeforeLast(mappedStatement.getId(), ".");// 当前类
        String currentMethodName = StringUtils.substringAfterLast(mappedStatement.getId(), ".");// 当前方法
        Method currentMethod = findMethod(className, currentMethodName);// 获取当前Method
        if (currentMethod == null || currentMethod.getAnnotation(MapF2F.class) == null) {// 如果当前Method没有注解MapF2F
            return invocation.proceed();
        }
        // 如果有MapF2F注解，则这里对结果进行拦截并转换
        MapF2F mapF2FAnnotation = currentMethod.getAnnotation(MapF2F.class);
        Statement statement = (Statement) invocation.getArgs()[0];
        Pair<Class<?>, Class<?>> kvTypePair = getKVTypeOfReturnMap(currentMethod);// 获取返回Map里key-value的类型
        TypeHandlerRegistry typeHandlerRegistry = mappedStatement.getConfiguration().getTypeHandlerRegistry();// 获取各种TypeHander的注册器
        return result2Map(statement, typeHandlerRegistry, kvTypePair, mapF2FAnnotation);
    }
    @Override
    public Object plugin(Object obj) {
        return Plugin.wrap(obj, this);
    }
    @Override
    public void setProperties(Properties properties) {
    }
    
    private Method findMethod(String className, String targetMethodName) throws Throwable {
        Method[] methods = Class.forName(className).getDeclaredMethods();// 该类所有声明的方法
        if (methods == null) {
            return null;
        }
        for (Method method : methods) {
            if (StringUtils.equals(method.getName(), targetMethodName)) {
                return method;
            }
        }
        return null;
    }
    
    private Pair<Class<?>, Class<?>> getKVTypeOfReturnMap(Method mapF2FMethod) {
        Type returnType = mapF2FMethod.getGenericReturnType();
        if (returnType instanceof ParameterizedType) {
            ParameterizedType parameterizedType = (ParameterizedType) returnType;
            if (!Map.class.equals(parameterizedType.getRawType())) {
                throw new RuntimeException(
                        "[ERROR-MapF2F-return-map-type]使用MapF2F,返回类型必须是java.util.Map类型！！！method=" + mapF2FMethod);
            }
            return new Pair<>((Class<?>) parameterizedType.getActualTypeArguments()[0],
                    (Class<?>) parameterizedType.getActualTypeArguments()[1]);
        }
        return new Pair<>(null, null);
    }
    
    private Object result2Map(Statement statement, TypeHandlerRegistry typeHandlerRegistry,
            Pair<Class<?>, Class<?>> kvTypePair, MapF2F mapF2FAnnotation) throws Throwable {
        ResultSet resultSet = statement.getResultSet();
        List<Object> res = new ArrayList();
        Map<Object, Object> map = new HashMap();
        while (resultSet.next()) {
            Object key = this.getObject(resultSet, 1, typeHandlerRegistry, kvTypePair.geTKEy());
            Object value = this.getObject(resultSet, 2, typeHandlerRegistry, kvTypePair.getValue());
            if (map.containsKey(key)) {// 该key已存在
                if (!mapF2FAnnotation.isAllowKeyRepeat()) {// 判断是否允许key重复
                    throw new DuplicateKeyException("MapF2F duplicated key!key=" + key);
                }
                Object preValue = map.get(key);
                if (!mapF2FAnnotation.isAllowValueDifferentWithSameKey() && !Objects.equals(value, preValue)) {// 判断是否允许value不同
                    throw new DuplicateKeyException("MapF2F different value with same key!key=" + key + ",value1="
                            + preValue + ",value2=" + value);
                }
            }
            map.put(key, value);// 第一列作为key,第二列作为value。
        }
        res.add(map);
        return res;
    }
    
    private Object getObject(ResultSet resultSet, int columnIndex, TypeHandlerRegistry typeHandlerRegistry,
            Class<?> javaType) throws SQLException {
        final TypeHandler<?> typeHandler = typeHandlerRegistry.hasTypeHandler(javaType)
                ? typeHandlerRegistry.getTypeHandler(javaType) : typeHandlerRegistry.getUnknownTypeHandler();
        return typeHandler.getResult(resultSet, columnIndex);
    }
}

2.3 ReflectUtil


package com.adu.spring_test.mybatis.util;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.SystemMetaObject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ReflectUtil {
    private static final Logger logger = LoggerFactory.getLogger(ReflectUtil.class);
    
    public static MetaObject getRealTarget(Invocation invocation) {
        MetaObject metaStatementHandler = SystemMetaObject.forObject(invocation.getTarget());
        while (metaStatementHandler.hasGetter("h")) {
            Object object = metaStatementHandler.getValue("h");
            metaStatementHandler = SystemMetaObject.forObject(object);
        }
        while (metaStatementHandler.hasGetter("target")) {
            Object object = metaStatementHandler.getValue("target");
            metaStatementHandler = SystemMetaObject.forObject(object);
        }
        return metaStatementHandler;
    }
}

2.4 MyBatis Datasource配置拦截器


<!-- session factory -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="configLocation" value="classpath:mybatis/mybatis-data-config.xml" />
        <property name="mapperLocations" value="classpath:mapper*.xml" />
        <property name="plugins">
            <array>
                <bean class="com.adu.spring_test.mybatis.interceptor.MapF2FInterceptor"/>
            </array>
        </property>
    </bean>

2.5 简例



@MapF2F()
Map<Long, String> queryUserNamesByIds(@Param("ids") List<Long> ids);


<select id="queryUserNamesByIds" resultType="map">
    SELECT id, user_name
    FROM user_info
    WHERE id IN
        <foreach collection="ids" open="(" close=")" separator="," item="item">
            #{item}
        </foreach>
</select>

以上为个人经验，希望能给大家一个参考，也希望大家多多支持编程网。

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本文标题: sql查询返回值使用map封装多个key和value实例

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