Mybatis 动态执行SQL语句

<dependency>
   <groupId>org.ow2.asm</groupId>
   <artifactId>asm</artifactId>
   <version>7.0</version>
</dependency>

import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.builder.xml.XMLMapperBuilder;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.defaults.DefaultSqlSessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
 
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.util.Map;
 
//from fhadmin.cn
@Component
@Slf4j
public class SqlExecutor {
 
    @Autowired
    private SqlSessionFactory sqlSessionFactory;
 
    public void parserString(String originSql,Map<String,Object> param) {
        StringBuilder builder = new StringBuilder();
        builder.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n");
        builder.append("<!DOCTYPE mapper PUBLIC \"-//mybatis.org//DTD Mapper 3.0//EN\" \"http://mybatis.org/dtd/mybatis-3-mapper.dtd\">\r\n");
        builder.append("<mapper namespace=\"cn.video.asm.TestMapper\">\r\n");
        builder.append("	 <select id=\"queryById\"  resultType=\"java.util.Map\">\r\n");
        builder.append(originSql);
        builder.append("	 </select>\r\n");
        builder.append("</mapper>");
        InputStream inputStream = new ByteArrayInputStream(builder.toString().getBytes());
        Configuration baseConfig = sqlSessionFactory.getConfiguration();
        // 不能使用原有的config对象加载，否则下次就不会重复加载导致传入的SQL语句不能切换
        // 也可以在这里指定数据源，从对应的数据源做查询动作
        Configuration configuration = new Configuration(baseConfig.getEnvironment());
        String resource = "resource";
        ErrorContext.instance().resource(resource);
        XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration,resource ,configuration.getSqlFragments());
        mapperParser.parse();
        SqlSession sqlSessionXML = new DefaultSqlSessionFactory(configuration).openSession();
        Object result = null;
        try {
            // 使用自定义的ClassLoader
            MyClassLoader loader = new MyClassLoader();
            // 生成二进制字节码
            byte[] bytes = MyClassLoader.dump();
            // 加载我们生成的 Mapper类
            Class<?> clazz = loader.defineClass("cn.video.asm.TestMapper", bytes);
            // 将生成的类对象加载到configuration中
            configuration.addMapper(clazz);
            Method query = clazz.getMethod("queryById", Map.class);
            // 这里就是通过类对象从configuration中获取对应的Mapper
            Object testMapper = sqlSessionXML.getMapper(clazz);
            result = query.invoke(testMapper, param);
        } catch (Exception e) {
            log.error("",e);
        }
        System.out.println("dyn : " + result);
    }
}

package cn.video.common;
 
import jdk.internal.org.objectweb.asm.ClassWriter;
import jdk.internal.org.objectweb.asm.MethodVisitor;
 
import static jdk.internal.org.objectweb.asm.Opcodes.*;
 
//from fhadmin.cn
public class MyClassLoader extends ClassLoader {
 
    public static byte[] dump() {
        ClassWriter cw = new ClassWriter(0);
        cw.visit(52, ACC_PUBLIC + ACC_ABSTRACT + ACC_INTERFACE, "cn/video/asm/TestMapper", null, "java/lang/Object", null);
        cw.visitSource("TestMapper.java", null);
        {
            MethodVisitor mv = cw.visitMethod(ACC_PUBLIC + ACC_ABSTRACT, "queryById", "(Ljava/util/Map;)Ljava/util/List;", "(Ljava/util/Map;)Ljava/util/List<Ljava/lang/Object;>;", null);
            mv.visitEnd();
        }
        cw.visitEnd();
        return cw.toByteArray();
    }
 
    public Class<?> defineClass(String name, byte[] b) {
        // ClassLoader是个抽象类，而ClassLoader.defineClass 方法是protected的
        // 所以我们需要定义一个子类将这个方法暴露出来
        Class<?> clazz = super.findLoadedClass(name);
        if (clazz != null) {
            return clazz;
        }
        return super.defineClass(name, b, 0, b.length);
    }
}