手写Mybatis-v1.0
源码链接（包括v1.0与v2.0）: https://github.com/staticLin/customMyBatis.git
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：
- SqlSession：含有属性Configuration、Excutor，含有方法getMapper，selectOne（先实现一个查询方法）
- Configuration：含有MapperRegistry（mapper接口、方法、SQL），含有方法getMapper
- 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）
/**
* @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(Class<T> clazz){
return configuration.getMapper(clazz, this);
}
/**
* 委派executor查询
*/
public <T> 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。
/**
* @description:
* @author: linyh
* @create: 2018-10-31 16:32
**/
public class CustomConfiguration {
public final MapperRegistory mapperRegistory = new MapperRegistory();
public static final Map<String, 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(Class<T> clazz, CustomSqlSession sqlSession) {
return mapperRegistory.getMapper(clazz, sqlSession);
}
}这里完善MapperProxy与MapperRegistory（注册所有的Mapper的Map）
/**
* @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 Map<Class<?>, 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(Class<T> 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(Class<T> 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<T>{
private Class<T> mapperInterface;
public MapperProxyFactory(Class<T> 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）。
/**
* @description:
* @author: linyh
* @create: 2018-10-31 16:32
**/
public interface CustomExecutor {
<T> T query(String statement, String parameter);
}
然后是具体的实现类，其中使用JDBC查询。
/**
* @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;
}
}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~
/**
* @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 + '\'' +
'}';
}
}/**
* @Author:linyh
* @Date: 2018/10/31 16:56
* @Modified By:
*/
public interface TestCustomMapper {
Test selectByPrimaryKey(int id);
}
/**
* @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：
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
- 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。
- 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
- 新增anontation功能动态扫描Mapper类，去掉HardCode。
- 新增StatementHandler设置参数以及负责查询工作。
- 新增ObjectFactory动态创建实体类。
- 新增ResultSetHandler将结果集映射到实体类中。
- 增加一个Plugin功能。
- 增加CacheExecutor装饰者来为查询增加一个缓存功能。