Mybatis-Plus取消自动转驼峰拦截器

背景

• 项目使用Mybatis-Plus，开启了全局结果集字段转驼峰map-underscore-to-camel-case: true。开启之后如果需要返回下划线需要自定义resultMap
• 现需要返回List<Map>，且返回的字段是动态变化，需要返回原Sql中的AS后的字段

版本

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>dynamic-datasource-spring-boot-starter</artifactId>
    <version>2.5.3</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.18</version>
</dependency>

解决

• 由于开启了map-underscore-to-camel-case: true全局驼峰，在org.apache.ibatis.executor.resultset.DefaultResultSetHandler#createAutomaticMappings方法中使用，且在com.baomidou.mybatisplus.extension.handlers.MybatisMapWrapper#findProperty方法中进行了转换。暂时没有找到其他的扩展点，故只能通过拦截器在结果集中处理
• 通过在拦截器中识别方法的注解，对结果进行拦截

@CancelCamelCase

import java.lang.annotation.*;

/**
 * @author wf
 * @date 2022年08月10日 11:14
 * @description SQL获取
 */
@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface CancelCamelCase {
}

CancelCamelCaseInterceptor

• 执行SQL之前先保存本身的下划线字段到一个map，然后等执行完SQL之后再还原回来

import com.alibaba.druid.pool.DruidPooledPreparedStatement;
import com.google.common.collect.Maps;
import com.wf.dev.common.annotaions.CancelCamelCase;
import org.apache.commons.lang3.StringUtils;
import org.apache.ibatis.executor.resultset.DefaultResultSetHandler;
import org.apache.ibatis.executor.resultset.ResultSetHandler;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.reflection.DefaultReflectorFactory;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.SystemMetaObject;
import org.assertj.core.util.Lists;
import org.springframework.stereotype.Component;

import java.lang.reflect.Method;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
import java.util.List;
import java.util.Map;
import java.util.Properties;

/**
 * @author wf
 * @date 2023年01月10日 10:40
 * @description 对mybatis查询单独取消map-underscore-to-camel-case为true
 */
@Component
@Intercepts(@Signature(type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class}))
public class CancelCamelCaseInterceptor implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        DefaultResultSetHandler resultSetHandler = (DefaultResultSetHandler) invocation.getTarget();
        MetaObject metaObject = MetaObject.forObject(resultSetHandler, SystemMetaObject.DEFAULT_OBJECT_FACTORY, SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY, new DefaultReflectorFactory());
        MappedStatement mappedStatement = (MappedStatement) metaObject.getValue("mappedStatement");
        String namespace = mappedStatement.getId();
        String className = StringUtils.substringBeforeLast(namespace, ".");
        Class<?> clazz = Class.forName(className);
        if (!clazz.isAnnotationPresent(CancelCamelCase.class)) {
            return invocation.proceed();
        }
        String methodName = StringUtils.substringAfterLast(namespace, ".");
        Method[] methods = clazz.getMethods();
        Method target = null;
        for (Method method : methods) {
            if (!method.getName().equals(methodName)) {
                continue;
            }
            target = method;
            break;
        }
        if (target == null || !target.isAnnotationPresent(CancelCamelCase.class)) {
            return invocation.proceed();
        }
        DruidPooledPreparedStatement ms = (DruidPooledPreparedStatement) invocation.getArgs()[0];
        ResultSet resultSet = ms.getResultSet();
        ResultSetMetaData metaData = resultSet.getMetaData();
        int columnCount = metaData.getColumnCount();
        Map<String, String> propertyColumnNameMap = Maps.newHashMap();
        for (int i = 1; i <= columnCount; i++) {
            // 这里必须要用getColumnLabel,不能用getColumnName
            String columnName = metaData.getColumnLabel(i);
            propertyColumnNameMap.put(com.baomidou.mybatisplus.core.toolkit.StringUtils.underlineToCamel(columnName), columnName);
        }
        Object proceed = invocation.proceed();
        if (!(proceed instanceof List)) {
            return proceed;
        }
        List list = (List) proceed;
        List<Map<String, Object>> result = Lists.newArrayList();
        for (Object row : list) {
            MetaObject metaObjectRow = MetaObject.forObject(row, SystemMetaObject.DEFAULT_OBJECT_FACTORY, SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY, new DefaultReflectorFactory());
            Map<String, Object> newRow = Maps.newHashMap();
            for (String property : propertyColumnNameMap.keySet()) {
                newRow.put(propertyColumnNameMap.get(property), metaObjectRow.getValue(property));
            }
            result.add(newRow);
        }
        return result;
    }

    @Override
    public Object plugin(Object target) {
        if (target instanceof ResultSetHandler) {
            return Plugin.wrap(target, this);
        }
        return target;
    }

    @Override
    public void setProperties(Properties properties) {

    }
}

Mapper

import org.apache.ibatis.annotations.Param;

import java.util.List;
import java.util.Map;

/**
 * @author wf
 * @date 2023年01月10日 15:07
 * @description
 */
@CancelCamelCase
public interface Mapper {

    /**
     * 从sql查询
     *
     * @param param
     * @return
     */
    @CancelCamelCase
    List<Map<String, Object>> sqlQuery(QueryParam param);
}

小结

• 此方法还是比较死板，增加了for循环，等于效率降低了。需要寻求更多的扩展

参考

• ResultSetMetaData.getColumnName踩坑记
• mybatis-plus返回map自动转驼峰配置