Mybatis源码分析之Mapper执行SQL过程（三）
今天我们来分析myabtis的sql是如何一步一步走到Excutor。
还是之前的demo
public static void main(String[] args) throws Exception {
SqlSessionFactory sessionFactory = ;String resource = "configuration.xml";sessionFactory = new SqlSessionFactoryBuilder.build(Resources.getResourceAsReader(resource));SqlSession sqlSession = sessionFactory.openSession;UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
System.out.println(userMapper.findUserById(1));
}
我们想看下基本的时序图有个大致了解
1:DefaultSqlSession获取getMapper
@Override
public T getMapper(Class type) {
return configuration.getMapper(type, this);
}
2:Configuration获取getMapper
public T getMapper(Class type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
Configuration和DefaultSqlSession什么都没有做，交给了MapperRegistry，我们看下MapperRegistry做了什么。
3：MapperRegistry获取getMapper
@SuppressWarnings("unchecked")
public T getMapper(Class type, SqlSession sqlSession) {
final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
if (mapperProxyFactory == ) {
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);
}}
通过knownMappers获取一个MapperProxyFactory，后然newInstance了一下，那么newInstance得到了什么东西呢？
4：MapperProxyFactory
@SuppressWarnings("unchecked")
protected T newInstance(MapperProxy mapperProxy) {
//java代理return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader, new Class { mapperInterface }, mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
final MapperProxy mapperProxy = new MapperProxy(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
通过以上的动态代理，咱们就可以方便地使用dao接口啦。到这里我们还没有看到任何执行sql有关的信息，或者说还没走到文章开始说的的Excutor， 我们看下MapperProxy代理类
MapperProxy
public class MapperProxy implements InvocationHandler, Serializable {
private static final long serialVersionUID = -6424540398559729838L;private final SqlSession sqlSession;private final Class mapperInterface;
private final Map methodCache;public MapperProxy(SqlSession sqlSession, Class mapperInterface, Map methodCache) {
this.sqlSession = sqlSession;this.mapperInterface = mapperInterface;
this.methodCache = methodCache;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {if (Object.class.equals(method.getDeclaringClass)) {try {return method.invoke(this, args);} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}}final MapperMethod mapperMethod = cachedMapperMethod(method);
return mapperMethod.execute(sqlSession, args);
}private MapperMethod cachedMapperMethod(Method method) {
MapperMethod mapperMethod = methodCache.get(method);
if (mapperMethod == ) {
mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration);
methodCache.put(method, mapperMethod);
}return mapperMethod;
}}
代理类交给了mapperMethod.execute进行处理，到这里我们只是看到了execute字眼了，我们继续往下看。
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;if (SqlCommandType.INSERT == command.getType) {Object param = method.convertArgsToSqlCommandParam(args);result = rowCountResult(sqlSession.insert(command.getName, param));} else if (SqlCommandType.UPDATE == command.getType) {Object param = method.convertArgsToSqlCommandParam(args);result = rowCountResult(sqlSession.update(command.getName, param));} else if (SqlCommandType.DELETE == command.getType) {Object param = method.convertArgsToSqlCommandParam(args);result = rowCountResult(sqlSession.delete(command.getName, param));} else if (SqlCommandType.SELECT == command.getType) {if (method.returnsVoid && method.hasResultHandler) {executeWithResultHandler(sqlSession, args);result = ;} else if (method.returnsMany) {result = executeForMany(sqlSession, args);} else if (method.returnsMap) {result = executeForMap(sqlSession, args);} else if (method.returnsCursor) {result = executeForCursor(sqlSession, args);} else {Object param = method.convertArgsToSqlCommandParam(args);result = sqlSession.selectOne(command.getName, param);}} else if (SqlCommandType.FLUSH == command.getType) {result = sqlSession.flushStatements;} else {throw new BindingException("Unknown execution method for: " + command.getName);}if (result == && method.getReturnType.isPrimitive && !method.returnsVoid) {throw new BindingException("Mapper method '" + command.getName
+ " attempted to return from a method with a primitive return type (" + method.getReturnType + ").");}return result;}
上面代码先是判断CRUD类型，然后根据类型去选择到底执行sqlSession中的哪个方法，我们现在是查询那么程序应该走到sqlSession.selectOne。
@Override
public T selectOne(String statement, Object parameter) {// Popular vote was to return on 0 results and throw exception on too many.List list = this.selectList(statement, parameter);if (list.size == 1) {return list.get(0);} else if (list.size > 1) {throw new TooManyResultsException("Expected one result (or ) to be returned by selectOne, but found: " + list.size);} else {return ;}}
@Override
public List selectList(String statement, Object parameter, RowBounds rowBounds) {try {MappedStatement ms = configuration.getMappedStatement(statement);
//终于看到我们要找的executor接口了return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);} catch (Exception e) {throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);} finally {ErrorContext.instance.reset;}}
我们终于看到executor类了， 调用了query方法，接下来的事情全部交给了executor处理了，
executor底层的分析已经在上一篇已经分享了。
我们代理执行sql的基本顺序是
MapperMethod.execute --> DefaultSqlSession.selectOne --> BaseExecutor.query --> SimpleExecutor.doQuery --> SimpleStatementHandler.query --> DefaultResultSetHandler.handleResultSets(Statement stmt) 最终得到数据。