前言

ps：最近在参与3100保卫战，战况很激烈，刚刚打完仗，来更新一下之前写了一半的博客。

该篇针对日常写查询的时候，那些动态条件sql 做个简单的封装，自动生成（抛砖引玉，搞个小玩具，不喜勿喷）。

正文

来看看我们平时写那些查询，基本上都要写的一些动态sql：

一个字段写一个if ，有没有人觉得烦的。

每张表的查询，很多都有这种需求，根据什么查询，根据什么查询，不为空就触发条件。

天天写天天写，copy 改，copy改，有没有人觉得烦的。

可能有看官看到这就会说，用插件自动生成就好了。
也有看官会说，用mybatis-plus就好了。

确实有道理，但是我就是想整个小玩具。你管我。

开整

本篇实现的封装小玩具思路：

①制定的规则（比如标记自定义注解 @JcSqlQuery 或是函数命名带上JcDynamics）。

② 触发的查询符合规则的，都自动去根据传参对象，不为空就自动组装 sql查询条件。

③ 利用mybatis @Select 注解，把默认表查询sql写好，顺便进到自定义的mybatis拦截器里面。

④组装完sql，就执行，完事。

先写mapper函数：

/*** @Author JCccc* @Description* @Date 2023/12/14 16:56*/
@Mapper
public interface DistrictMapper {@Select("select code,name,parent_code,full_name  FROM s_district_info")List<District> queryListJcDynamics(District district);@Select("select code,name,parent_code,full_name  FROM s_district_info")District queryOneJcDynamics(District district);}

然后是ParamClassInfo.java 这个用于收集需要参与动态sql组装的类：

import lombok.Data;/*** @Author JCccc* @Description* @Date 2021/12/14 16:56*/
@Data
public class ParamClassInfo {private  String classType;private  Object keyValue;private  String  keyName;}

然后是一个自定义的mybatis拦截器(这里面写了一些小函数实现自主组装，下面有图解) ：

MybatisInterceptor.java

import com.example.dotest.entity.ParamClassInfo;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.*;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.springframework.beans.BeanUtils;
import org.springframework.stereotype.Component;
import org.springframework.util.CollectionUtils;
import org.springframework.util.ReflectionUtils;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;
import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;import static java.util.regex.Pattern.*;/*** @Author JCccc* @Description* @Date 2021/12/14 16:56*/
@Component
@Intercepts({@Signature(type = Executor.class, method = "update", args = {MappedStatement.class, Object.class}),@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})
})
public class MybatisInterceptor implements Interceptor {private final static String JC_DYNAMICS = "JcDynamics";@Overridepublic Object intercept(Invocation invocation) throws Throwable {//获取执行参数Object[] objects = invocation.getArgs();MappedStatement ms = (MappedStatement) objects[0];Object objectParam = objects[1];List<ParamClassInfo> paramClassInfos = convertParamList(objectParam);String queryConditionSqlScene = getQueryConditionSqlScene(paramClassInfos);//解析执行sql的map方法,开始自定义规则匹配逻辑String mapperMethodAllName = ms.getId();int lastIndex = mapperMethodAllName.lastIndexOf(".");String mapperClassStr = mapperMethodAllName.substring(0, lastIndex);String mapperClassMethodStr = mapperMethodAllName.substring((lastIndex + 1));Class<?> mapperClass = Class.forName(mapperClassStr);Method[] methods = mapperClass.getMethods();for (Method method : methods) {if (method.getName().equals(mapperClassMethodStr) && mapperClassMethodStr.contains(JC_DYNAMICS)) {BoundSql boundSql = ms.getSqlSource().getBoundSql(objects[1]);String originalSql = boundSql.getSql().toLowerCase(Locale.CHINA).replace("[\\t\\n\\r]", " ");//进行自动的 条件拼接String newSql = originalSql + queryConditionSqlScene;BoundSql newBoundSql = new BoundSql(ms.getConfiguration(), newSql,boundSql.getParameterMappings(), boundSql.getParameterObject());MappedStatement newMs = newMappedStatement(ms, new MyBoundSqlSqlSource(newBoundSql));for (ParameterMapping mapping : boundSql.getParameterMappings()) {String prop = mapping.getProperty();if (boundSql.hasAdditionalParameter(prop)) {newBoundSql.setAdditionalParameter(prop, boundSql.getAdditionalParameter(prop));}}Object[] queryArgs = invocation.getArgs();queryArgs[0] = newMs;System.out.println("打印新SQL语句" + newSql);}}//继续执行逻辑return invocation.proceed();}private String getQueryConditionSqlScene(List<ParamClassInfo> paramClassInfos) {StringBuilder conditionParamBuilder = new StringBuilder();if (CollectionUtils.isEmpty(paramClassInfos)) {return "";}conditionParamBuilder.append("  WHERE ");int size = paramClassInfos.size();for (int index = 0; index < size; index++) {ParamClassInfo paramClassInfo = paramClassInfos.get(index);String keyName = paramClassInfo.getKeyName();//默认驼峰拆成下划线 ，比如 userName -》 user_name ,   name -> name//如果是需要取别名，其实可以加上自定义注解这些，但是本篇例子是轻封装，思路给到，你们i自己玩String underlineKeyName = camelToUnderline(keyName);conditionParamBuilder.append(underlineKeyName);Object keyValue = paramClassInfo.getKeyValue();String classType = paramClassInfo.getClassType();//其他类型怎么处理 ，可以按照类型区分 ，比如检测到一组开始时间，Date 拼接 between and等
//            if (classType.equals("String")){
//                conditionParamBuilder .append("=").append("\'").append(keyValue).append("\'");
//            }conditionParamBuilder.append("=").append("\'").append(keyValue).append("\'");if (index != size - 1) {conditionParamBuilder.append(" AND ");}}return conditionParamBuilder.toString();}private static List<ParamClassInfo> convertParamList(Object obj) {List<ParamClassInfo> paramClassList = new ArrayList<>();for (PropertyDescriptor pd : BeanUtils.getPropertyDescriptors(obj.getClass())) {if (!"class".equals(pd.getName())) {if (ReflectionUtils.invokeMethod(pd.getReadMethod(), obj) != null) {ParamClassInfo paramClassInfo = new ParamClassInfo();paramClassInfo.setKeyName(pd.getName());paramClassInfo.setKeyValue(ReflectionUtils.invokeMethod(pd.getReadMethod(), obj));paramClassInfo.setClassType(pd.getPropertyType().getSimpleName());paramClassList.add(paramClassInfo);}}}return paramClassList;}public static String camelToUnderline(String line){if(line==null||"".equals(line)){return "";}line=String.valueOf(line.charAt(0)).toUpperCase().concat(line.substring(1));StringBuffer sb=new StringBuffer();Pattern pattern= compile("[A-Z]([a-z\\d]+)?");Matcher matcher=pattern.matcher(line);while(matcher.find()){String word=matcher.group();sb.append(word.toUpperCase());sb.append(matcher.end()==line.length()?"":"_");}return sb.toString();}@Overridepublic Object plugin(Object o) {//获取代理权if (o instanceof Executor) {//如果是Executor（执行增删改查操作），则拦截下来return Plugin.wrap(o, this);} else {return o;}}/*** 定义一个内部辅助类，作用是包装 SQL*/class MyBoundSqlSqlSource implements SqlSource {private BoundSql boundSql;public MyBoundSqlSqlSource(BoundSql boundSql) {this.boundSql = boundSql;}@Overridepublic BoundSql getBoundSql(Object parameterObject) {return boundSql;}}private MappedStatement newMappedStatement(MappedStatement ms, SqlSource newSqlSource) {MappedStatement.Builder builder = newMappedStatement.Builder(ms.getConfiguration(), ms.getId(), newSqlSource, ms.getSqlCommandType());builder.resource(ms.getResource());builder.fetchSize(ms.getFetchSize());builder.statementType(ms.getStatementType());builder.keyGenerator(ms.getKeyGenerator());if (ms.getKeyProperties() != null && ms.getKeyProperties().length > 0) {builder.keyProperty(ms.getKeyProperties()[0]);}builder.timeout(ms.getTimeout());builder.parameterMap(ms.getParameterMap());builder.resultMaps(ms.getResultMaps());builder.resultSetType(ms.getResultSetType());builder.cache(ms.getCache());builder.flushCacheRequired(ms.isFlushCacheRequired());builder.useCache(ms.isUseCache());return builder.build();}@Overridepublic void setProperties(Properties properties) {//读取mybatis配置文件中属性}

代码简析：

驼峰转换下划线，用于转出数据库表的字段：

通过反射把 sql入参的对象不为空的属性名和对应的值，拿出来：

组件动态查询的sql 语句：

写个简单测试用例：

    @AutowiredDistrictMapper districtMapper;@Testpublic void test() {District query = new District();query.setCode("110000");query.setName("北京市");District district = districtMapper.queryOneJcDynamics(query);System.out.println(district.toString());District listQuery = new District();listQuery.setParentCode("110100");List<District> districts = districtMapper.queryListJcDynamics(listQuery);System.out.println(districts.toString());}

看下效果，可以看到都自动识别把不为空的字段属性和值拼接成查询条件了：