Mybatis源码分析-执行模块

执行模块打算分几篇记录，先大概了解下整体流程，再详细讲些个人感觉重要的点。

接着上篇例子讲

String resource = "configs/mybatis-config.xml";
Reader reader = Resources.getResourceAsReader(resource);
SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(reader);
SqlSession session = sqlSessionFactory.openSession();
try {
AppMapper mapper = session.getMapper(AppMapper.class);
List<App> blog = mapper.selectByFilter(null);
System.out.println(JsonUtil.objectToJson(blog));
} finally {
session.close();
}

上篇已经粗略介绍过配置初始化的代码，这篇来看看 代码中try块中的代码！

1 AppMapper mapper = session.getMapper(AppMapper.class); 获取代理mapper类

从上篇应该知道，此时的session的真正执行者是DefaultSqlSession，来看看其getMapper方法

@Override
public <T> T getMapper(Class<T> type) {
return configuration.<T>getMapper(type, this);
}

实现了Configuration的getMapper方法

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}

实现了MapperRegistry的getMapper方法

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);
}
}

实现了 MapperProxyFactory的newInstance方法

protected T newInstance(MapperProxy<T> mapperProxy) {
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}

public T newInstance(SqlSession sqlSession) {
final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}

终于到正主了，可以看到，在这里实现了代理了，代理是MapperProxy并且返回

2 List blog = mapper.selectByFilter(null);

获取到mapper代理后，执行了selectByFilter方法，既然是代理类，执行的方法就应该是MapperProxy类中的invoke方法，我们来看看

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);
}
final MapperMethod mapperMethod = cachedMapperMethod(method);
return mapperMethod.execute(sqlSession, args);
}

Object.class.equals(method.getDeclaringClass()) 这个判断基本上可以没用了，我们一般都是用接口

往下走，出现MapperMethod，来看看他的execute方法

public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
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()) {
executeWithResultHandler(sqlSession, args);
result = null;
} 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);
}
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;
}

我们的例子中走的是 executeForMany方法，返回列表

private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
List<E> result;
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
result = sqlSession.<E>selectList(command.getName(), param, rowBounds);
} else {
result = sqlSession.<E>selectList(command.getName(), param);
}
// issue #510 Collections & arrays support
if (!method.getReturnType().isAssignableFrom(result.getClass())) {
if (method.getReturnType().isArray()) {
return convertToArray(result);
} else {
return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
}
}
return result;
}

好吧，绕了大圈 ，又回到sqlSession.selectList方法

public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
MappedStatement ms = configuration.getMappedStatement(statement);
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();
}
}

终于到了执行器这里了，此时的executor是CachingExecutor代理，先从缓存过一遍，如果不存在，则从库中获取

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
Set<Method> methods = signatureMap.get(method.getDeclaringClass());
if (methods != null && methods.contains(method)) {
return interceptor.intercept(new Invocation(target, method, args));
}
return method.invoke(target, args);
} catch (Exception e) {
throw ExceptionUtil.unwrapThrowable(e);
}
}

从代理中走了一圈，看看是否有插件的存在，有插件则走插件，无插件走原方法，咱这里没插件！

public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
BoundSql boundSql = ms.getBoundSql(parameterObject);
CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}

这里先不讲缓存了，继续经过一级缓存的判断，没有的情况下，继续执行SimpleExecutor执行器

list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;

二级缓存的判断，也没有，则

list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);

从数据库中获取数据

public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
Configuration configuration = ms.getConfiguration();
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
stmt = prepareStatement(handler, ms.getStatementLog());
return handler.<E>query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}

终于出现Statement关键类了

StatementHandler 四大类之一

private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
Connection connection = getConnection(statementLog);
stmt = handler.prepare(connection, transaction.getTimeout());
handler.parameterize(stmt);
return stmt;
}

分析下 这块

Connection connection = getConnection(statementLog);

这个方法里面涉及到数据连接池（当然你也可以配置不用连接池，但为什么不用呢？），也就是说 优先从连接池中获取链接，如果过期，则删除过期链接重新生成一个链接。连接池具体怎么样不是本篇内容。然后返回的链接时一个ConnectionLogger的代理，来看看invoke内容

public Object invoke(Object proxy, Method method, Object[] params)
throws Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, params);
}
if ("prepareStatement".equals(method.getName())) {
if (isDebugEnabled()) {
debug(" Preparing: " + removeBreakingWhitespace((String) params[0]), true);
}
PreparedStatement stmt = (PreparedStatement) method.invoke(connection, params);
stmt = PreparedStatementLogger.newInstance(stmt, statementLog, queryStack);
return stmt;
} else if ("prepareCall".equals(method.getName())) {
if (isDebugEnabled()) {
debug(" Preparing: " + removeBreakingWhitespace((String) params[0]), true);
}
PreparedStatement stmt = (PreparedStatement) method.invoke(connection, params);
stmt = PreparedStatementLogger.newInstance(stmt, statementLog, queryStack);
return stmt;
} else if ("createStatement".equals(method.getName())) {
Statement stmt = (Statement) method.invoke(connection, params);
stmt = StatementLogger.newInstance(stmt, statementLog, queryStack);
return stmt;
} else {
return method.invoke(connection, params);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}

好吗 在使用connection生成Statment的时候，就执行了该invoke内容了。

stmt = PreparedStatementLogger.newInstance(stmt, statementLog, queryStack);

又使用代理，返回PreparedStatementLogger代理

到此 Statement 已经创建好了

public Object invoke(Object proxy, Method method, Object[] params) throws Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, params);
}
if (EXECUTE_METHODS.contains(method.getName())) {
if (isDebugEnabled()) {
debug("Parameters: " + getParameterValueString(), true);
}
clearColumnInfo();
if ("executeQuery".equals(method.getName())) {
ResultSet rs = (ResultSet) method.invoke(statement, params);
return rs == null ? null : ResultSetLogger.newInstance(rs, statementLog, queryStack);
} else {
return method.invoke(statement, params);
}
} else if (SET_METHODS.contains(method.getName())) {
if ("setNull".equals(method.getName())) {
setColumn(params[0], null);
} else {
setColumn(params[0], params[1]);
}
return method.invoke(statement, params);
} else if ("getResultSet".equals(method.getName())) {
ResultSet rs = (ResultSet) method.invoke(statement, params);
return rs == null ? null : ResultSetLogger.newInstance(rs, statementLog, queryStack);
} else if ("getUpdateCount".equals(method.getName())) {
int updateCount = (Integer) method.invoke(statement, params);
if (updateCount != -1) {
debug("   Updates: " + updateCount, false);
}
return updateCount;
} else {
return method.invoke(statement, params);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}

接下来Statement每一个操作都会进入PreparedStatementLogger的invoke方法中 ，可见 它只处理executeQuery，setNull，getResultSet，getUpdateCount的方法调用，其他还是调用原方法

接下来 是ParameterHandler，四大类之一，主要是处理参数的操作

@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
ps.execute();
return resultSetHandler.<E> handleResultSets(ps);
}

走到PreparedStatementHandler中的query方法，执行sql语句了，接下来就是对结果集的处理了，ResultSetHandler四大类之一，主要处理结果数据转换！

public List<Object> handleResultSets(Statement stmt) throws SQLException {
ErrorContext.instance().activity("handling results").object(mappedStatement.getId());

final List<Object> multipleResults = new ArrayList<Object>();

int resultSetCount = 0;
//获得执行的字段、字段类型等信息
ResultSetWrapper rsw = getFirstResultSet(stmt);
//获得结果配置信息
List<ResultMap> resultMaps = mappedStatement.getResultMaps();
int resultMapCount = resultMaps.size();
validateResultMapsCount(rsw, resultMapCount);
while (rsw != null && resultMapCount > resultSetCount) {
ResultMap resultMap = resultMaps.get(resultSetCount);
//对结果数据进行处理，生成实体类，循环行数据，给实体类赋值，方法中还需要考虑到类型转换器
handleResultSet(rsw, resultMap, multipleResults, null);
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
}

String[] resultSets = mappedStatement.getResultSets();
if (resultSets != null) {
while (rsw != null && resultSetCount < resultSets.length) {
ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
if (parentMapping != null) {
String nestedResultMapId = parentMapping.getNestedResultMapId();
ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
handleResultSet(rsw, resultMap, null, parentMapping);
}
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
}
}

return collapseSingleResultList(multipleResults);
}

private void handleResultSet(ResultSetWrapper rsw, ResultMap resultMap, List<Object> multipleResults, ResultMapping parentMapping) throws SQLException {
try {
if (parentMapping != null) {
handleRowValues(rsw, resultMap, null, RowBounds.DEFAULT, parentMapping);
} else {
if (resultHandler == null) {
DefaultResultHandler defaultResultHandler = new DefaultResultHandler(objectFactory);
//赋值
handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);
multipleResults.add(defaultResultHandler.getResultList());
} else {
handleRowValues(rsw, resultMap, resultHandler, rowBounds, null);
}
}
} finally {
// issue #228 (close resultsets)
closeResultSet(rsw.getResultSet());
}
}

private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping)
throws SQLException {
DefaultResultContext<Object> resultContext = new DefaultResultContext<Object>();
skipRows(rsw.getResultSet(), rowBounds);
while (shouldProcessMoreRows(resultContext, rowBounds) && rsw.getResultSet().next()) {
ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(rsw.getResultSet(), resultMap, null);
Object rowValue = getRowValue(rsw, discriminatedResultMap);
storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet());
}
}

//获取数据赋值
private boolean applyPropertyMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, ResultLoaderMap lazyLoader, String columnPrefix)
throws SQLException {
final List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
boolean foundValues = false;
final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
//循环执行获取行数据
for (ResultMapping propertyMapping : propertyMappings) {
//字段
String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
if (propertyMapping.getNestedResultMapId() != null) {
// the user added a column attribute to a nested result map, ignore it
column = null;
}
if (propertyMapping.isCompositeResult()
|| (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH)))
|| propertyMapping.getResultSet() != null) {
//真实值
Object value = getPropertyMappingValue(rsw.getResultSet(), metaObject, propertyMapping, lazyLoader, columnPrefix);
// issue #541 make property optional
final String property = propertyMapping.getProperty();
if (property == null) {
continue;
} else if (value == DEFERED) {
foundValues = true;
continue;
}
if (value != null) {
foundValues = true;
}
if (value != null || (configuration.isCallSettersOnNulls() && !metaObject.getSetterType(property).isPrimitive())) {
// gcode issue #377, call setter on nulls (value is not 'found')
//通过该方法进行赋值，通过set方法将值set进去
metaObject.setValue(property, value);
}
}
}
return foundValues;
}

private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap) throws SQLException {
final ResultLoaderMap lazyLoader = new ResultLoaderMap();
//获得实体类
Object rowValue = createResultObject(rsw, resultMap, lazyLoader, null);
if (rowValue != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
final MetaObject metaObject = configuration.newMetaObject(rowValue);
boolean foundValues = this.useConstructorMappings;
if (shouldApplyAutomaticMappings(resultMap, false)) {
foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, null) || foundValues;
}
//实体类赋值
foundValues = applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, null) || foundValues;
foundValues = lazyLoader.size() > 0 || foundValues;
rowValue = (foundValues || configuration.isReturnInstanceForEmptyRow()) ? rowValue : null;
}
return rowValue;
}

private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, ResultLoaderMap lazyLoader, String columnPrefix) throws SQLException {
this.useConstructorMappings = false; // reset previous mapping result
final List<Class<?>> constructorArgTypes = new ArrayList<Class<?>>();
final List<Object> constructorArgs = new ArrayList<Object>();
//生成实体类，这里用到ObjectFactory，即配置中介绍的可以实现实体类初始化
Object resultObject = createResultObject(rsw, resultMap, constructorArgTypes, constructorArgs, columnPrefix);
if (resultObject != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
//循环配置结果集
for (ResultMapping propertyMapping : propertyMappings) {
// 判断是否延迟加载
if (propertyMapping.getNestedQueryId() != null && propertyMapping.isLazy()) {
resultObject = configuration.getProxyFactory().createProxy(resultObject, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
break;
}
}
}
this.useConstructorMappings = (resultObject != null && !constructorArgTypes.isEmpty()); // set current mapping result
return resultObject;
}

好了 获得结果就返回，最后关闭连接，不过这里用到连接池，不会真正的关闭。

这两篇mybatis有代码，而且代码占多，并且没有注释，还是想着自己看懂就行了毕竟是粗略的过一下，这种想法不是很好，接下来几篇尽量能注释好吧！！

接下来将逐步分析以下几个模块，一个个来吧！！

1 数据源

2 缓存

3 事务

4 插件