MyBatis-plus如何执行自定义SQL

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionTemplate;
import org.springframework.beans.factory.annotation.Autowired;

import java.sql.SQLException;

public class TestMySql {
    @Autowired
    private SqlSessionTemplate sqlSessionTemplate;

    //    自定义执行SQL
    public void mySql() throws SQLException {
        String sql = "select * from User";
        SqlSession sqlSession = openSession();
        sqlSession.getConnection().prepareStatement(sql);
        closeSession(sqlSession);
    }

    //    开启链接
    private SqlSession openSession() {
        SqlSessionFactory sqlSessionFactory = sqlSessionTemplate.getSqlSessionFactory();
        return sqlSessionFactory.openSession();
    }

    //    关闭链接
    private void closeSession(SqlSession sqlSession) {
        sqlSession.close();
    }
}

String sql = "Select * From User";
sqlMapper.explainQuery(sql);

@SqlParser(filter = true)
void explainQuery(String sql);

<update id="explainQuery">
  ${templateName,jdbcType=VARCHAR}
</update>

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import java.util.List;
public interface MyBaseMapper<T> extends BaseMapper<T> {
    List<T> findAll();
}

import com.baomidou.mybatisplus.core.enums.SqlMethod;
import com.baomidou.mybatisplus.core.injector.AbstractMethod;
import com.baomidou.mybatisplus.core.metadata.TableInfo;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlSource;

public class FindAll extends AbstractMethod {
    @Override
    public MappedStatement injectMappedStatement(Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo) {
        String sqlMethod = "findAll";
        String sql = "select * from " + tableInfo.getTableName();
        SqlSource sqlSource = languageDriver.createSqlSource(configuration, sql, modelClass);
        return this.addSelectMappedStatement(mapperClass, sqlMethod, sqlSource, modelClass, tableInfo);
    }
}

import com.baomidou.mybatisplus.core.injector.AbstractMethod;
import com.baomidou.mybatisplus.core.injector.DefaultSqlInjector;

import java.util.List;

public class MySqlInjector extends DefaultSqlInjector {
    @Override
    public List<AbstractMethod> getMethodList() {
        List<AbstractMethod> methodList = super.getMethodList();
        methodList.add(new FindAll()); // 再扩充自定义的方法
        list.add(new FindAll());
        return methodList;
    }
}

import com.baomidou.mybatisplus.core.injector.AbstractMethod;
import com.baomidou.mybatisplus.core.injector.DefaultSqlInjector;

import java.util.List;

public class MySqlInjector extends DefaultSqlInjector {
    @Override
    public List<AbstractMethod> getMethodList() {
        List<AbstractMethod> methodList = super.getMethodList();
        methodList.add(new FindAll()); // 再扩充自定义的方法
        list.add(new FindAll());
        return methodList;
    }
}

### 2.4、注册到Spring容器

```java
/*** 自定义SQL注入器 */
@Bean
public MySqlInjector mySqlInjector() {
    return new MySqlInjector();
}

@Test
public void testFindAll() {
    List<User> users = this.userMapper.findAll();
    for (User user : users) {
        System.out.println(user);
    }
}