mybatis框架的简单实现

本mybatis只是简单实现，实现mybatis的一部分核心功能。

思路：

1. 解析配置文件，得到数据库配置及mapper相关信息
2. 创建实体类封装解析到的数据
3. 通过动态代理执行sql语句

mapper实体类封装UserMapper.xml的数据：

package com.zhijin.framwork;

public class Mapper {
    private String id ;
    private String resultType ;
    private String sql ;
    private String tag ;
    private String namespace ;


    public Mapper() {
    }

    public Mapper(String id, String resultType, String sql, String tag, String namespace) {
        this.id = id;
        this.resultType = resultType;
        this.sql = sql;
        this.tag = tag;
        this.namespace = namespace;
    }


    public String getId() {
        return id;
    }


    public void setId(String id) {
        this.id = id;
    }


    public String getResultType() {
        return resultType;
    }


    public void setResultType(String resultType) {
        this.resultType = resultType;
    }
    public String getSql() {
        return sql;
    }


    public void setSql(String sql) {
        this.sql = sql;
    }


    public String getTag() {
        return tag;
    }


    public void setTag(String tag) {
        this.tag = tag;
    }


    public String getNamespace() {
        return namespace;
    }


    public void setNamespace(String namespace) {
        this.namespace = namespace;
    }

    public String toString() {
        return "Mapper{id = " + id + ", resultType = " + resultType + ", sql = " + sql + ", tag = " + tag + ", namespace = " + namespace + "}";
    }
}

创建Configuration封装sqlMapConfig.xml配置

package com.zhijin.framwork;

public class Mapper {
    private String id ;
    private String resultType ;
    private String sql ;
    private String tag ;
    private String namespace ;


    public Mapper() {
    }

    public Mapper(String id, String resultType, String sql, String tag, String namespace) {
        this.id = id;
        this.resultType = resultType;
        this.sql = sql;
        this.tag = tag;
        this.namespace = namespace;
    }


    public String getId() {
        return id;
    }


    public void setId(String id) {
        this.id = id;
    }


    public String getResultType() {
        return resultType;
    }


    public void setResultType(String resultType) {
        this.resultType = resultType;
    }
    public String getSql() {
        return sql;
    }


    public void setSql(String sql) {
        this.sql = sql;
    }


    public String getTag() {
        return tag;
    }


    public void setTag(String tag) {
        this.tag = tag;
    }


    public String getNamespace() {
        return namespace;
    }


    public void setNamespace(String namespace) {
        this.namespace = namespace;
    }

    public String toString() {
        return "Mapper{id = " + id + ", resultType = " + resultType + ", sql = " + sql + ", tag = " + tag + ", namespace = " + namespace + "}";
    }
}

德鲁伊数据库连接池工厂：

package com.zhijin.utils;

import com.alibaba.druid.pool.DruidDataSourceFactory;
import com.zhijin.framwork.Configuration;
import com.zhijin.framwork.SqlSession;

import javax.sql.DataSource;
import java.io.IOException;
import java.util.Properties;

public class DruidFactoryUtils {
    private static DataSource dataSource ;

    static {
        try {
            Configuration configuration = new Configuration();
            Properties properties = new Properties();
            properties.setProperty("driverClassName",configuration.getDriver());
            properties.setProperty("url",configuration.getUrl());
            properties.setProperty("username",configuration.getUsername());
            properties.setProperty("password",configuration.getPassword());

            dataSource = DruidDataSourceFactory.createDataSource(properties);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void close(SqlSession sqlSession){
        try {
            if (sqlSession!=null) {
                sqlSession.close();
            }
        } catch (IOException e) {
                e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession(){
        SqlSession sqlSession = new SqlSession();
        try {
            sqlSession.setConnection(dataSource.getConnection());
        } catch (Exception e) {
            e.printStackTrace();
        }
        return sqlSession;
    }

}

动态代理执行sql

package com.zhijin.framwork;


import java.io.Closeable;
import java.io.IOException;
import java.lang.reflect.*;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

public class SqlSession implements Closeable {
    private Connection connection ;

    public Connection getConnection() {
        return connection;
    }

    public void setConnection(Connection connection) {
        this.connection = connection;
    }

    @Override
    public void close() throws IOException {

    }

    /**
     * 通过动态代理执行查询
     * @param obj
     * @param <T>
     * @return
     */
    public <T> T getMapper(Class obj) {
        return (T) Proxy.newProxyInstance(obj.getClassLoader(), new Class[]{obj}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //1.通过Configuration自加载得到sql语句并执行
                Configuration configuration = new Configuration();
                List<Mapper> mappers = configuration.getMappers();
                Mapper currentMapper =null;
                for (Mapper mapper : mappers) {
                    if (mapper.getNamespace().equals(obj.getName())&& mapper.getId().equals(method.getName())){
                        currentMapper = mapper;
                        break;
                    }
                }
                String sql = currentMapper.getSql();
                PreparedStatement pstm = connection.prepareStatement(sql);
                List<Object> datas = new ArrayList<>();
                if (currentMapper.getTag().equals("select")){
                    //处理结果集，封装到list集合中返回给调用
                    ResultSet rs = pstm.executeQuery();
                    while (rs.next()){
                        String resultType = currentMapper.getResultType();
                        Class clazz = Class.forName(resultType);
                        Object data = clazz.getDeclaredConstructor().newInstance();

                        Field[] fields = clazz.getDeclaredFields();
                        for (Field field : fields) {
                            field.setAccessible(true);
                            field.set(data,rs.getObject(field.getName()));
                        }
                        datas.add(data);
                        return  datas;
                    }
                }else if (currentMapper.getTag().equalsIgnoreCase("update") 
                        || currentMapper.getTag().equalsIgnoreCase("delete") 
                        || currentMapper.getTag().equalsIgnoreCase("insert")){
                    int rows = pstm.executeUpdate();
                    return rows;
                }else {
                    pstm.execute();
                }
                return null;
            }
        });
    }
}

测试类：

package com.zhijin.text;


import com.zhijin.bean.User;
import com.zhijin.dao.UserMapper;
import com.zhijin.framwork.SqlSession;
import com.zhijin.utils.DruidFactoryUtils;
import org.junit.Test;

import java.util.List;

public class MybatisTest {

    /**
     * 测试查询全部
     */
    @Test
    public void selectAll()   {
        SqlSession sqlSession = DruidFactoryUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = userMapper.findAll();
        System.out.println(users);
        DruidFactoryUtils.close(sqlSession);
    }
}