mybatis blinding模块分析---sqlsesion.getMapper()方法实现原理
问题：通常我们调用一个mapper接口方法是如何实现的？例如下面代码
List<User> users= mapper.queryUser(param);
在解析原理前先看看一下类：
- MapperRegistry： mapper 接口和对应的代理对象工厂的注册中心；
- MapperProxyFactory：用于生成 mapper 接口动态代理的实例对象；保证 Mapper 实例对象是局部变量；
- MapperProxy：实现了 InvocationHandler 接口，它是增强 mapper 接口的实现；
- MapperMethod：封装了 Mapper 接口中对应方法的信息，以及对应的 sql 语句的信息；它是 mapper 接口与映射配置文件中 sql 语句的桥梁； MapperMethod 对象不记录任何状态信息，所以它可以在多个代理对象之间共享；
代码入口位置：
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
package org.apache.ibatis.session;
import java.io.Closeable;
import java.sql.Connection;
import java.util.List;
import java.util.Map;
import org.apache.ibatis.cursor.Cursor;
import org.apache.ibatis.executor.BatchResult;
public interface SqlSession extends Closeable {
<T> T selectOne(String var1);
<T> T selectOne(String var1, Object var2);
<E> List<E> selectList(String var1);
<E> List<E> selectList(String var1, Object var2);
<E> List<E> selectList(String var1, Object var2, RowBounds var3);
<K, V> Map<K, V> selectMap(String var1, String var2);
<K, V> Map<K, V> selectMap(String var1, Object var2, String var3);
<K, V> Map<K, V> selectMap(String var1, Object var2, String var3, RowBounds var4);
<T> Cursor<T> selectCursor(String var1);
<T> Cursor<T> selectCursor(String var1, Object var2);
<T> Cursor<T> selectCursor(String var1, Object var2, RowBounds var3);
void select(String var1, Object var2, ResultHandler var3);
void select(String var1, ResultHandler var2);
void select(String var1, Object var2, RowBounds var3, ResultHandler var4);
int insert(String var1);
int insert(String var1, Object var2);
int update(String var1);
int update(String var1, Object var2);
int delete(String var1);
int delete(String var1, Object var2);
void commit();
void commit(boolean var1);
void rollback();
void rollback(boolean var1);
List<BatchResult> flushStatements();
void close();
void clearCache();
Configuration getConfiguration();
//获取mapper对象
<T> T getMapper(Class<T> var1);
Connection getConnection();
}
获取到代理工厂：
说明在mybatis初始化时configuration对象记录了mapper的代理工厂的注册中心
/*mapper接口的动态代理注册中心*/ protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
DefaultSqlSession里面的getMapper方法获取到
@Override
public <T> T getMapper(Class<T> type) {
return configuration.<T>getMapper(type, this);
}
//获取到代理工厂注册类MapperRegistry
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
获取到动态代理工厂
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}
获取到MapperProxy，实现对mapper接口的实现
protected T newInstance(MapperProxy<T> mapperProxy) {
//创建实现了mapper接口的动态代理对象
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
MapperProxy实现了InvocationHandler；进入MapperProxy对象的invoke方法：
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, args);
} else if (isDefaultMethod(method)) {
return invokeDefaultMethod(proxy, method, args);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
//从缓存中获取mapperMethod对象，如果缓存中没有，则创建一个，并添加到缓存中
final MapperMethod mapperMethod = cachedMapperMethod(method);
//调用execute方法执行sql
return mapperMethod.execute(sqlSession, args);
}
实际调用的核心代码：mapperMethod.execute
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
//第一步 根据sql语句类型选择调用不同的方法
switch (command.getType()) {
case INSERT: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(), param));
break;
}
case UPDATE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(), param));
break;
}
case DELETE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(), param));
break;
}
case SELECT:
if (method.returnsVoid() && method.hasResultHandler()) {//返回值为void
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {//返回值为集合或者数组
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {//返回值为map
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {//返回值为游标
result = executeForCursor(sqlSession, args);
} else {//处理返回为单一对象的情况
//通过参数解析器解析解析参数
Object param = method.convertArgsToSqlCommandParam(args);
result = sqlSession.selectOne(command.getName(), param);
if (method.returnsOptional() &&
(result == null || !method.getReturnType().equals(result.getClass()))) {
result = OptionalUtil.ofNullable(result);
}
}
break;
case FLUSH:
result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for: " + command.getName());
}
if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
throw new BindingException("Mapper method '" + command.getName()
+ " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
}
return result;
}
总结：mapper动态代理增强的方式实际上还是会调用sqlSession里面的方法
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