系列
- mybatis-3.4.6 配置介绍
- mybatis-3.4.6 顶层配置解析
- mybatis-3.4.6 子配置解析
- mybatis-3.4.6 mapper解析
- mybatis-3.4.6 SQL执行流程
- mybatis-3.4.6 SqlSession执行过程
- mybatis-3.4.6 缓存介绍
- mybatis-3.4.6 自增主键
- mybatis-3.4.6 foreach 自增主键
- mybatis-3.4.6 事务管理
开篇
- 这个系列是基于mybatis-3.4.6版本的源码解析，这篇文章是梳理基于SqlSessionFactory的mybatis的整体执行流程，文章更侧重于整体流程的梳理。
- mybatis基于SqlSessionFactory的执行包含四步骤，分别是构建SqlSessionFactory、构建SqlSession对象，获取mapper对象、执行SQL语句。
demo举例
public class MybatisHelloWorld {
public static void main(String[] args) {
String resouce = "configuration.xml";
Reader reader;
try {
reader = Resources.getResourceAsReader(resouce);
// 1、构建SqlSessionFactory对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
// 2、构建SqlSession对象
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
// 3、获取mapper对象
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
// 4、执行SQL语句
ImcUser imcUser = userMapper.getById(1,"nick");
System.out.println("xxxxxx " + imcUser.getUserNick());
} finally {
sqlSession.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
- 1、构建SqlSessionFactory对象，其中SqlSessionFactory是根据配置文件build生成。
- 2、构建SqlSession对象，通过sqlSessionFactory.openSession获取SqlSession对象。
- 3、获取mapper对象，通过sqlSession.getMapper获取mapper对象。
- 4、通过mapper的方法执行SQL语句，通过调用mapper的interface对应的方法获取数据。
执行过程分析
执行流程图
mybatis执行流程图
- 整体的执行过程如mybatis执行流程图所示。
- 核心步骤一是返回MapperProxy对象。
- 核心步骤二是通过MapperProxy对象执行execute。
- 核心步骤三是通过MapperMethod来执行请求。
DefaultSqlSessionFactory
public class DefaultSqlSessionFactory implements SqlSessionFactory {
private final Configuration configuration;
public DefaultSqlSessionFactory(Configuration configuration) {
this.configuration = configuration;
}
@Override
public SqlSession openSession() {
return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
final Environment environment = configuration.getEnvironment();
// 创建事务相关
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
// 创建executor对象
final Executor executor = configuration.newExecutor(tx, execType);
// 核心在于创建DefaultSqlSession对象
return new DefaultSqlSession(configuration, executor, autoCommit);
} catch (Exception e) {
closeTransaction(tx); // may have fetched a connection so lets call close()
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
}
- DefaultSqlSessionFactory的openSessionFromDataSource方法负责创建DefaultSqlSession对象。
- DefaultSqlSession对象的变量包括all-in-one的configuration，执行的Executor对象等。
DefaultSqlSession
public class DefaultSqlSession implements SqlSession {
private final Configuration configuration;
private final Executor executor;
private final boolean autoCommit;
private boolean dirty;
private List> cursorList;
public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
this.configuration = configuration;
this.executor = executor;
this.dirty = false;
this.autoCommit = autoCommit;
}
@Override
public T getMapper(Class type) {
return configuration.getMapper(type, this);
}
}
- DefaultSqlSession的目前核心在于根据type返回mapper对象。
getMapper
public class Configuration {
protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
public T getMapper(Class type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
}
- Configuration的mapperRegistry维持着mapper和MapperProxyFactory。
- mapperRegistry是整个mapper代理的核心数据结构。
public class MapperRegistry {
private final Configuration config;
private final Map, MapperProxyFactory> knownMappers = new HashMap, MapperProxyFactory>();
public MapperRegistry(Configuration config) {
this.config = config;
}
@SuppressWarnings("unchecked")
public T getMapper(Class type, SqlSession sqlSession) {
final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
try {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}
- MapperRegistry通过knownMappers维持mapper类和MapperProxyFactory的映射关系。
- getMapper通过mapperProxyFactory.newInstance来创建代理类。
MapperProxyFactory
public class MapperProxyFactory {
private final Class mapperInterface;
private final Map methodCache = new ConcurrentHashMap();
public MapperProxyFactory(Class mapperInterface) {
this.mapperInterface = mapperInterface;
}
public Class getMapperInterface() {
return mapperInterface;
}
public Map getMethodCache() {
return methodCache;
}
@SuppressWarnings("unchecked")
protected T newInstance(MapperProxy mapperProxy) {
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);
}
}
- MapperProxyFactory的newInstance主要是创建mapper的接口对应的proxy对象MapperProxy。
- newInstance返回是通过jdk的动态代理生成的新对象。
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;
}
@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);
}
// 通过MapperMethod来执行流程
final MapperMethod mapperMethod = cachedMapperMethod(method);
// 执行mapperMethod的execute方法
return mapperMethod.execute(sqlSession, args);
}
private MapperMethod cachedMapperMethod(Method method) {
MapperMethod mapperMethod = methodCache.get(method);
if (mapperMethod == null) {
mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
methodCache.put(method, mapperMethod);
}
return mapperMethod;
}
}
- MapperProxy会新建MapperMethod对象并执行其execute方法。
- MapperMethod的execute方法相当于串联了真正执行SQL的命令。
MapperMethod
public class MapperMethod {
private final SqlCommand command;
private final MethodSignature method;
public MapperMethod(Class mapperInterface, Method method, Configuration config) {
this.command = new SqlCommand(config, mapperInterface, method);
this.method = new MethodSignature(config, mapperInterface, method);
}
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);
if (method.returnsOptional()
&& (result == null || !method.getReturnType().equals(result.getClass()))) {
result = Optional.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;
}
}
- MapperMethod会创建SqlCommand对象并执行具体的SQL。
- MapperMethod的execute本质上是通过sqlSession实现真正的执行逻辑。
SqlCommand
public class MapperMethod {
public static class SqlCommand {
private final String name;
private final SqlCommandType type;
public SqlCommand(Configuration configuration, Class mapperInterface, Method method) {
final String methodName = method.getName();
final Class declaringClass = method.getDeclaringClass();
// 解析MappedStatement
MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass,
configuration);
if (ms == null) {
if (method.getAnnotation(Flush.class) != null) {
name = null;
type = SqlCommandType.FLUSH;
} else {
throw new BindingException("Invalid bound statement (not found): "
+ mapperInterface.getName() + "." + methodName);
}
} else {
name = ms.getId();
type = ms.getSqlCommandType();
if (type == SqlCommandType.UNKNOWN) {
throw new BindingException("Unknown execution method for: " + name);
}
}
}
public String getName() {
return name;
}
public SqlCommandType getType() {
return type;
}
private MappedStatement resolveMappedStatement(Class mapperInterface, String methodName,
Class declaringClass, Configuration configuration) {
String statementId = mapperInterface.getName() + "." + methodName;
if (configuration.hasStatement(statementId)) {
return configuration.getMappedStatement(statementId);
} else if (mapperInterface.equals(declaringClass)) {
return null;
}
for (Class superInterface : mapperInterface.getInterfaces()) {
if (declaringClass.isAssignableFrom(superInterface)) {
MappedStatement ms = resolveMappedStatement(superInterface, methodName,
declaringClass, configuration);
if (ms != null) {
return ms;
}
}
}
return null;
}
}
}
- SqlCommand的构造函数会解析MappedStatement对象，根据mapperInterface.getName() + "." + methodName从Configuration的mappedStatements获取mappedStatement对象。
- mappedStatements是在解析mapper的配置文件过程中生成的。
- 本质上SqlCommand的创建过程关联了mapper的Interface和XML的SQL定义。
SqlSessionFactory类关系图
DefaultSqlSessionFactory
SqlSession
参考文章
- 源码参考
- mybatis官网介绍
- 深入理解mybatis原理
- Mybatis3.4.x技术内幕
- mybatis 3.x源码深度解析与最佳实践