自己动手实现一个简单的Mybatis（初级版本1.0）
mybatis,mybatis源码
mybatis源码
发布日期:   2021-04-05
作者:   欧阳思海
文章字数:   2.1k
阅读时长:   10 分
阅读次数:  
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原文链接：blog.ouyangsihai.cn >> 自己动手实现一个简单的Mybatis（初级版本1.0）

手写Mybatis-v1.0

**源码链接（包括v1.0与v2.0）: **

从上一个文章 —Mybatis概述中了解到了Mybatis的主要架构与底层原理流程，结尾给出了一个宏观流程图，可以知道，大致我们可以从三个模块入手：

  1. SqlSession：含有属性Configuration、Excutor，含有方法getMapper，selectOne（先实现一个查询方法）
  2. Configuration：含有MapperRegistry（mapper接口、方法、SQL），含有方法getMapper
  3. Executor：含有方法doQuery查询数据库

这样来看，我们的MyBatis1.0的大致脉络已经出来了。接下来就coding吧~

先是自定义的SqlSession （这里忽略SqlSessionFactory解析xml资源过程，1.0版本简化）

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/** * @description: 自定义的SqlSession * @author: linyh * @create: 2018-10-31 16:31 **/public class CustomSqlSession {     //持有两个关键对象    private CustomConfiguration configuration;    private CustomExecutor executor;     /**     * 用构造器将两个对象形成关系     */    public CustomSqlSession(CustomConfiguration configuration, CustomExecutor executor) {        this.configuration = configuration;        this.executor = executor;    }     public CustomConfiguration getConfiguration() {        return configuration;    }     /**    * 委派configuration获取mapper    */    public T T getMapper(ClassT clazz){        return configuration.getMapper(clazz, this);    }     /**     * 委派executor查询     */    public T T selectOne(String statement, String parameter){        return executor.query(statement, parameter);    }}

/**

  • @description: 自定义的SqlSession
  • @author: linyh
  • @create: 2018-10-31 16:31

**/
public class CustomSqlSession {


//持有两个关键对象
private CustomConfiguration configuration;
private CustomExecutor executor;

/**
 * 用构造器将两个对象形成关系
 */
public CustomSqlSession(CustomConfiguration configuration, CustomExecutor executor) {
    this.configuration = configuration;
    this.executor = executor;
}

public CustomConfiguration getConfiguration() {
    return configuration;
}

/**
* 委派configuration获取mapper
*/
public  T getMapper(Class clazz){
    return configuration.getMapper(clazz, this);
}

/**
 * 委派executor查询
 */
public  T selectOne(String statement, String parameter){
    return executor.query(statement, parameter);
}

}

然后是自定义Configuration实现getMapper方法，这里也初始化一个MapperProxyFactory为了存放所有的Mapper。再写一个验证Mapper是否存在的方法和根据Class获取对应mapper的MapperProxyFactory。

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/** * @description: * @author: linyh * @create: 2018-10-31 16:32 **/public class CustomConfiguration {     public final MapperRegistory mapperRegistory = new MapperRegistory();     public static final MapString, String mappedStatements = new HashMap();     //TODO 改用anontation扫描 (暂时HardCode)    //初始化时Configuration加载所有Mapper方法与Sql语句    public CustomConfiguration() {        mapperRegistory.addMapper(TestMapper.class);        mappedStatements.put("com.test.mybatis.v1.mapper.TestCustomMapper.selectByPrimaryKey"        , "select * from test where id = %d");    }     //MapperProxy根据statementName查找是否有对应SQL    public boolean hasStatement(String statementName) {        return mappedStatements.containsKey(statementName);    }     //MapperProxy根据statementID获取SQL    public String getMappedStatement(String id) {        return mappedStatements.get(id);    }     public T T getMapper(ClassT clazz, CustomSqlSession sqlSession) {        return mapperRegistory.getMapper(clazz, sqlSession);    }}

/**

  • @description:
  • @author: linyh
  • @create: 2018-10-31 16:32

**/
public class CustomConfiguration {


public final MapperRegistory mapperRegistory = new MapperRegistory();

public static final MapString, String mappedStatements = new HashMap();

//TODO 改用anontation扫描 (暂时HardCode)
//初始化时Configuration加载所有Mapper方法与Sql语句
public CustomConfiguration() {
    mapperRegistory.addMapper(TestMapper.class);
    mappedStatements.put("com.test.mybatis.v1.mapper.TestCustomMapper.selectByPrimaryKey"
    , "select * from test where id = %d");
}

//MapperProxy根据statementName查找是否有对应SQL
public boolean hasStatement(String statementName) {
    return mappedStatements.containsKey(statementName);
}

//MapperProxy根据statementID获取SQL
public String getMappedStatement(String id) {
    return mappedStatements.get(id);
}

public  T getMapper(Class clazz, CustomSqlSession sqlSession) {
    return mapperRegistory.getMapper(clazz, sqlSession);
}

}

这里完善MapperProxy与MapperRegistory（注册所有的Mapper的Map）

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/** * @description: Mapper动态代理者 * @author: linyh * @create: 2018-10-31 16:52 **/public class MapperProxy implements InvocationHandler{     private CustomSqlSession sqlSession;     public MapperProxy(CustomSqlSession sqlSession) {        this.sqlSession = sqlSession;    }     /**     * 每一个Mapper的每个方法都将执行invoke方法，此方法判断方法名是否维护在Configuration中，如有则取出SQL    */    @Override    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {        if (sqlSession.getConfiguration().hasStatement(method.getDeclaringClass().getName()+"."+method.getName())) {            String sql = sqlSession.getConfiguration().getMappedStatement(method.getDeclaringClass().getName()+"."+method.getName());            return sqlSession.selectOne(sql, args[0].toString());        }        return method.invoke(proxy, args);    }}

/**

  • @description: Mapper动态代理者
  • @author: linyh
  • @create: 2018-10-31 16:52

**/
public class MapperProxy implements InvocationHandler{


private CustomSqlSession sqlSession;

public MapperProxy(CustomSqlSession sqlSession) {
    this.sqlSession = sqlSession;
}

/**
 * 每一个Mapper的每个方法都将执行invoke方法，此方法判断方法名是否维护在Configuration中，如有则取出SQL
*/
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (sqlSession.getConfiguration().hasStatement(method.getDeclaringClass().getName()+"."+method.getName())) {
        String sql = sqlSession.getConfiguration().getMappedStatement(method.getDeclaringClass().getName()+"."+method.getName());
        return sqlSession.selectOne(sql, args[0].toString());
    }
    return method.invoke(proxy, args);
}

}

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/** * @description: mapper注册类 * @author: linyh * @create: 2018-10-31 16:51 **/public class MapperRegistory {     //用一个Map维护所有Mapper    private final MapClass?, MapperProxyFactory knownMappers = new HashMap();     //TODO Configuration解析anontation之后调用方法初始化所有mapper    public T void addMapper(ClassT clazz){        knownMappers.put(clazz, new MapperProxyFactory(clazz));    }     /**     * getMapper最底层执行者，获取mapper的MapperProxyFactory对象     */    public T T getMapper(ClassT clazz, CustomSqlSession sqlSession) {        MapperProxyFactory proxyFactory = knownMappers.get(clazz);        if (proxyFactory == null) {            throw new RuntimeException("Type: " + clazz + " can not find");        }        return (T)proxyFactory.newInstance(sqlSession);    }     /**     * 内部类实现一个Factory生成Mapper的代理     */    public class MapperProxyFactoryT{         private ClassT mapperInterface;         public MapperProxyFactory(ClassT mapperInterface) {            this.mapperInterface = mapperInterface;        }         public T newInstance(CustomSqlSession sqlSession) {            return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, new MapperProxy(sqlSession));        }    }}

/**

  • @description: mapper注册类
  • @author: linyh
  • @create: 2018-10-31 16:51

**/
public class MapperRegistory {


//用一个Map维护所有Mapper
private final MapClass?, MapperProxyFactory knownMappers = new HashMap();

//TODO Configuration解析anontation之后调用方法初始化所有mapper
public  void addMapper(Class clazz){
    knownMappers.put(clazz, new MapperProxyFactory(clazz));
}

/**
 * getMapper最底层执行者，获取mapper的MapperProxyFactory对象
 */
public  T getMapper(Class clazz, CustomSqlSession sqlSession) {
    MapperProxyFactory proxyFactory = knownMappers.get(clazz);
    if (proxyFactory == null) {
        throw new RuntimeException("Type: " + clazz + " can not find");
    }
    return (T)proxyFactory.newInstance(sqlSession);
}

/**
 * 内部类实现一个Factory生成Mapper的代理
 */
public class MapperProxyFactory{

    private Class mapperInterface;

    public MapperProxyFactory(Class mapperInterface) {
        this.mapperInterface = mapperInterface;
    }

    public T newInstance(CustomSqlSession sqlSession) {
        return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, new MapperProxy(sqlSession));
    }
}

}

到这里getMapper就实现好了，每次getMapper都能生成对应的MapperProxy代理。接下来实现Executor的查询方法。

先定义一个接口（2.0将加入CacheExecutor，面向接口编程便于扩展）。

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/** * @description: * @author: linyh * @create: 2018-10-31 16:32 **/public interface CustomExecutor {    T T query(String statement, String parameter);}

/**

  • @description:
  • @author: linyh
  • @create: 2018-10-31 16:32

**/
public interface CustomExecutor {
T query(String statement, String parameter);
}

然后是具体的实现类，其中使用JDBC查询。

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/** * @description: 自定义Executor * @author: linyh * @create: 2018-10-31 17:46 **/public class CustomDefaultExecutor implements CustomExecutor{     @Override    public T T query(String statement, String parameter) {        Connection conn = null;        PreparedStatement preparedStatement = null;        Test test = null;        try {            conn = getConnection();             //TODO ParameterHandler            preparedStatement = conn.prepareStatement(String.format(statement, Integer.parseInt(parameter)));            preparedStatement.execute();            ResultSet rs = preparedStatement.getResultSet();             //TODO ObjectFactory            test = new Test();             //TODO ResultSetHandler            while (rs.next()) {                test.setId(rs.getInt(1));                test.setNums(rs.getInt(2));                test.setName(rs.getString(3));            }         } catch (SQLException e) {            e.printStackTrace();        } finally {            try {                conn.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        return (T)test;    }     public Connection getConnection() throws SQLException {        String driver = "com.mysql.jdbc.Driver";        String url = "jdbc:mysql://127.0.0.1:3306/gp?serverTimezone=UTC";        String username = "root";        String password = "admin";        Connection conn = null;        try {            Class.forName(driver); //classLoader,加载对应驱动            conn = DriverManager.getConnection(url, username, password);        } catch (ClassNotFoundException e) {            e.printStackTrace();        } catch (SQLException e) {            e.printStackTrace();        }        return conn;    }}

/**

  • @description: 自定义Executor
  • @author: linyh
  • @create: 2018-10-31 17:46

**/
public class CustomDefaultExecutor implements CustomExecutor{


@Override
public  T query(String statement, String parameter) {
    Connection conn = null;
    PreparedStatement preparedStatement = null;
    Test test = null;
    try {
        conn = getConnection();

        //TODO ParameterHandler
        preparedStatement = conn.prepareStatement(String.format(statement, Integer.parseInt(parameter)));
        preparedStatement.execute();
        ResultSet rs = preparedStatement.getResultSet();

        //TODO ObjectFactory
        test = new Test();

        //TODO ResultSetHandler
        while (rs.next()) {
            test.setId(rs.getInt(1));
            test.setNums(rs.getInt(2));
            test.setName(rs.getString(3));
        }

    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    return (T)test;
}

public Connection getConnection() throws SQLException {
    String driver = "com.mysql.jdbc.Driver";
    String url = "jdbc:mysql://127.0.0.1:3306/gp?serverTimezone=UTC";
    String username = "root";
    String password = "admin";
    Connection conn = null;
    try {
        Class.forName(driver); //classLoader,加载对应驱动
        conn = DriverManager.getConnection(url, username, password);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return conn;
}

}

这样查询方法也大致完成了，创建实体与Mapper，然后开始测试一下吧~

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/** * @description: 实体类 * @author: linyh * @create: 2018-10-31 17:03 **/public class Test {     private Integer id;    private Integer nums;    private String name;     public Integer getId() {        return id;    }     public void setId(Integer id) {        this.id = id;    }     public Integer getNums() {        return nums;    }     public void setNums(Integer nums) {        this.nums = nums;    }     public String getName() {        return name;    }     public void setName(String name) {        this.name = name;    }     @Override    public String toString() {        return "Test{" +                "id=" + id +                ", nums=" + nums +                ", name='" + name + '\'' +                '}';    }}

/**

  • @description: 实体类
  • @author: linyh
  • @create: 2018-10-31 17:03

**/
public class Test {


private Integer id;
private Integer nums;
private String name;

public Integer getId() {
    return id;
}

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

public Integer getNums() {
    return nums;
}

public void setNums(Integer nums) {
    this.nums = nums;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

@Override
public String toString() {
    return "Test{" +
            "id=" + id +
            ", nums=" + nums +
            ", name='" + name + '\'' +
            '}';
}

}

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/** * @Author:linyh * @Date: 2018/10/31 16:56 * @Modified By: */public interface TestCustomMapper {    Test selectByPrimaryKey(int id);}

/**

  • @Author:linyh
  • @Date: 2018/10/31 16:56
  • @Modified By:

*/
public interface TestCustomMapper {
Test selectByPrimaryKey(int id);
}

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/** * @description: * @author: linyh * @create: 2018-10-31 18:05 **/public class TestMybatis {    public static void main(String[] args) {        CustomSqlSession sqlSession = new CustomSqlSession(                new CustomConfiguration(), new CustomDefaultExecutor());        TestCustomMapper testCustomMapper = sqlSession.getMapper(TestCustomMapper.class);        System.out.println(testCustomMapper.selectByPrimaryKey(2));    }}

/**

  • @description:
  • @author: linyh
  • @create: 2018-10-31 18:05

**/
public class TestMybatis {
public static void main(String[] args) {
CustomSqlSession sqlSession = new CustomSqlSession(
new CustomConfiguration(), new CustomDefaultExecutor());
TestCustomMapper testCustomMapper = sqlSession.getMapper(TestCustomMapper.class);
System.out.println(testCustomMapper.selectByPrimaryKey(2));
}
}

控制台打印：

自己动手实现一个简单的Mybatis（初级版本1.0）

这样就完成了极简版MyBatisv1.0了，其中还有很多不足之处，我用了TODO标记，下面总结几点不足之处，统计2.0需要改进与增加的功能。

不足之处

  1. 解析Mapper信息时用了HardCode，需改用anontation方式去扫描Mapper与对应SQL语句。
  2. Executor不够单一职责，它不仅负责参数装配还负责查询语句加上结果集映射，不合理，需要细分职责。

增加的功能

  1. 新增anontation功能动态扫描Mapper类，去掉HardCode。
  2. 新增StatementHandler设置参数以及负责查询工作。
  3. 新增ObjectFactory动态创建实体类。
  4. 新增ResultSetHandler将结果集映射到实体类中。
  5. 增加一个Plugin功能。
  6. 增加CacheExecutor装饰者来为查询增加一个缓存功能。
本人花费半年的时间总结的《Java面试指南》已拿腾讯等大厂offer，已开源在github ，欢迎star！

本文GitHub https://github.com/OUYANGSIHAI/JavaInterview 已收录，这是我花了6个月总结的一线大厂Java面试总结，本人已拿大厂offer，欢迎star

原文链接：blog.ouyangsihai.cn >> 自己动手实现一个简单的Mybatis（初级版本1.0）

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