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_NAME3.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。
