mybaties核心组件概念
Configuration:用于描述 MyBatis 主配置文件信息,MyBatis 框架在启动时自动配置类中,会加载mapper配置文件,将配置信息转换为 Configuration 对象,然后把该对象传入给sqlSessionFactory供后续使用。
SqlSession:面向用户的 API,是 MyBatis 与数据库交互的接口。
Executor:SQL 执行器,用于和数据库交互。SqlSession 可以理解为 Executor 组件的外观(外观模式),真正执行 SQL 的是 Executor 组件。
MappedStatement:用于描述 SQL 配置信息,MyBatis 框架启动时,XML 文件或者注解配置的 SQL信息会被转换为 MappedStatement 对象注册到 Configuration 组件中。
StatementHandler:封装了对 JDBC 中 Statement 对象的操作,包括为 Statement 参数占位符设置值,通过 Statement 对象执行 SQL语句。
TypeHandler:类型处理器,用于 Java 类型与 JDBC 类型之间的转换。
ParameterHandler:用于处理 SQL 中的参数占位符,为参数占位符设置值。
ResultSetHandler:封装了对 ResultSet 对象的处理逻辑,将结果集转换为 Java 实体对象。
mybaties主要逻辑点
- mybaties自动配置流程
- mybaties mapper接口动态代理注入到spring中流程
- sql执行流程
下面就围绕这三掉来分析下mybaties的源码和执行流程
mybaties自动配置流程
mybaties mapper接口动态代理注入到spring中流程
sql执行流程
图中根据执行逻辑分成了三大块。
蓝色部分:通过调用MapperFactoryBean的getObject方法生成mapper对应的动态代理。
红色部分:调用mapper方法的时候,触发对应动态代理拦截对应的方法。
绿色部分:
sqlsession执行一条sql的逻辑。主要先从configration中获取对应的MappedStatement,然后创建
Executor执行器(默认是SimpleExecutor),执行器流程:
- 获取StatementHandler,先执行jdbc的prepare,
- 然后用ParameterHandler把mapper方法中传入的参数(对象或者值)解析后设置到Jdbc的statement中。
- 执行jdbc execute方法,去执行具体的sql。
- ResultSetHandler调用handleCursorResultSets方法处理查询返回的结果,主要是进行对象的映射处理。最后把结果再依次返回。
mybaties自动配置流程
配置入口类MybatisAutoConfiguration
@Bean
@ConditionalOnMissingBean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
factory.setDataSource(dataSource);
factory.setVfs(SpringBootVFS.class);
if (StringUtils.hasText(this.properties.getConfigLocation())) {
factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
}
applyConfiguration(factory);
if (this.properties.getConfigurationProperties() != null) {
factory.setConfigurationProperties(this.properties.getConfigurationProperties());
}
if (!ObjectUtils.isEmpty(this.interceptors)) {
factory.setPlugins(this.interceptors);
}
if (this.databaseIdProvider != null) {
factory.setDatabaseIdProvider(this.databaseIdProvider);
}
if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
}
if (this.properties.getTypeAliasesSuperType() != null) {
factory.setTypeAliasesSuperType(this.properties.getTypeAliasesSuperType());
}
if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
}
if (!ObjectUtils.isEmpty(this.typeHandlers)) {
factory.setTypeHandlers(this.typeHandlers);
}
if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
factory.setMapperLocations(this.properties.resolveMapperLocations());
}
Set<String> factoryPropertyNames = Stream
.of(new BeanWrapperImpl(SqlSessionFactoryBean.class).getPropertyDescriptors()).map(PropertyDescriptor::getName)
.collect(Collectors.toSet());
Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {
// Need to mybatis-spring 2.0.2+
factory.setScriptingLanguageDrivers(this.languageDrivers);
if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {
defaultLanguageDriver = this.languageDrivers[0].getClass();
}
}
if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) {
// Need to mybatis-spring 2.0.2+
factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver);
}
return factory.getObject();
}
@Bean
@ConditionalOnMissingBean
public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
ExecutorType executorType = this.properties.getExecutorType();
if (executorType != null) {
return new SqlSessionTemplate(sqlSessionFactory, executorType);
} else {
return new SqlSessionTemplate(sqlSessionFactory);
}
}
这个类没啥好说的,主要看sqlSessionFactory,它是通过SqlSessionFactoryBean的getObject生成的。
继续看getObject方法,里面主要就是调用了buildSqlSessionFactory方法
protected SqlSessionFactory buildSqlSessionFactory() throws Exception {
...省略不关心代码
for (Resource mapperLocation : this.mapperLocations) {
if (mapperLocation == null) {
continue;
}
try {
// 解析mapper对应的xml文件,它会把xml解析成一个个的MappedStatement,即每个查询标签都会被解析成一个MappedStatement
// 解析完后,会间接存入Configuration中。
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
xmlMapperBuilder.parse();
} catch (Exception e) {
throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
} finally {
ErrorContext.instance().reset();
}
LOGGER.debug(() -> "Parsed mapper file: '" + mapperLocation + "'");
}
...省略不关心代码
// 创建sqlSessionFactory类,并把targetConfiguration作为参数
return this.sqlSessionFactoryBuilder.build(targetConfiguration);
}
经过此步骤后,mybaties中mapper的解析工作已经完成了,后续就可以通过动态代理拦截方法,去执行sql了。
mybaties mapper接口动态代理注入到spring中流程
MapperScan
@Import(MapperScannerRegistrar.class)
@Repeatable(MapperScans.class)
public @interface MapperScan {
}
MapperScannerRegistrar
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
AnnotationAttributes mapperScanAttrs = AnnotationAttributes
.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
if (mapperScanAttrs != null) {
registerBeanDefinitions(importingClassMetadata, mapperScanAttrs, registry,
generateBaseBeanName(importingClassMetadata, 0));
}
}
void registerBeanDefinitions(AnnotationMetadata annoMeta, AnnotationAttributes annoAttrs,
BeanDefinitionRegistry registry, String beanName) {
// 指定BeanDefinition对应的类,这里是MapperScannerConfigurer,这个类很重要后续会解释
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
builder.addPropertyValue("processPropertyPlaceHolders", true);
... 省去不重要代码
// 设置mapperFactoryBeanClass属性,这个是MapperFactoryBean,最终就是调用它的getObject方法,生成对应mapper的动态代理,
//,然后注入到spring中的
Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
builder.addPropertyValue("mapperFactoryBeanClass", mapperFactoryBeanClass);
}
// 可以直接定义覆盖默认的sqlSessionTemplateRef
String sqlSessionTemplateRef = annoAttrs.getString("sqlSessionTemplateRef");
if (StringUtils.hasText(sqlSessionTemplateRef)) {
builder.addPropertyValue("sqlSessionTemplateBeanName", annoAttrs.getString("sqlSessionTemplateRef"));
}
// 可以直接定义覆盖默认的sqlSessionFactory,比如配置多数据源的时候,可以定义自己的fatory
String sqlSessionFactoryRef = annoAttrs.getString("sqlSessionFactoryRef");
if (StringUtils.hasText(sqlSessionFactoryRef)) {
builder.addPropertyValue("sqlSessionFactoryBeanName", annoAttrs.getString("sqlSessionFactoryRef"));
}
// 要扫描的mapper路径,只会把该路径下的mapper注册成动态代理
List<String> basePackages = new ArrayList<>();
basePackages.addAll(
Arrays.stream(annoAttrs.getStringArray("value")).filter(StringUtils::hasText).collect(Collectors.toList()));
basePackages.addAll(Arrays.stream(annoAttrs.getStringArray("basePackages")).filter(StringUtils::hasText)
.collect(Collectors.toList()));
basePackages.addAll(Arrays.stream(annoAttrs.getClassArray("basePackageClasses")).map(ClassUtils::getPackageName)
.collect(Collectors.toList()));
if (basePackages.isEmpty()) {
basePackages.add(getDefaultBasePackage(annoMeta));
}
String lazyInitialization = annoAttrs.getString("lazyInitialization");
if (StringUtils.hasText(lazyInitialization)) {
builder.addPropertyValue("lazyInitialization", lazyInitialization);
}
builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(basePackages));
// 把MapperScannerConfigurer类生成对应,并且注入到spring容器中
registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
}
上面方法会把MapperScannerConfigurer实例化,并且注入到容器中。
MapperScannerConfigurer类创建成功后会调用它的postProcessBeanDefinitionRegistry方法,该方法属于BeanDefinitionRegistryPostProcessor接口,注册了BeanDefinition后,spring会触发该方法,所以再分析该方法。
MapperScannerConfigurer
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
if (this.processPropertyPlaceHolders) {
processPropertyPlaceHolders();
}
// 核心类,主要是扫描指定的mapper路径下所有的mapper接口,然后注入到spring的时候,注入的名字还是接口名
// 但是注入的实际类替换成了MapperFactoryBean,该类是一个FactoryBean,当调用它的getObject的时候,会生成
// 对应接口的动态代理
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
scanner.setAddToConfig(this.addToConfig);
scanner.setAnnotationClass(this.annotationClass);
scanner.setMarkerInterface(this.markerInterface);
scanner.setSqlSessionFactory(this.sqlSessionFactory);
scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
scanner.setResourceLoader(this.applicationContext);
scanner.setBeanNameGenerator(this.nameGenerator);
// 设置MapperFactoryBean类
scanner.setMapperFactoryBeanClass(this.mapperFactoryBeanClass);
if (StringUtils.hasText(lazyInitialization)) {
scanner.setLazyInitialization(Boolean.valueOf(lazyInitialization));
}
scanner.registerFilters();
// 调用scan,把对应包路径下的所有类,注入到spring容器中
scanner.scan(
StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
ClassPathMapperScanner继承了ClassPathBeanDefinitionScanner,该类的san方法可以扫描指定路径下的所有类,并把他们注入到spring容器中。
经过上面这个方法后,指定mapper路径下的所有接口,会以动态代理的方式注入到spring容器中。
sql执行流程
上面分析了动态代理生成的核心类是MapperFactoryBean的getObject方法,这里先分析动态代理生成逻辑
MapperFactoryBean
public T getObject() throws Exception {
return getSqlSession().getMapper(this.mapperInterface);
}
会调用到
SqlSessionTemplate
public <T> T getMapper(Class<T> type) {
// 这里获取Configuration类,然后调用getMapper方法。
return getConfiguration().getMapper(type, this);
}
最后会调用到这里,创建动态代理
MapperProxyFactory
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<>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
上面可以看到动态代理拦截方法类是MapperProxy,当执行动态代理对应方法的时候,会先执行该类的拦截方法invoke -> cachedInvoker ,最后调用到的拦截方法是MapperMethod的execute,如下:
MapperMethod
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
// 根据不同的类型,来不行不同的方法
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()) {
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;
}
private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
List<E> result;
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
// 执行sqlSession的方法,其实这里是sqlSessionTemplate,具体可以看前面传入的参数
result = sqlSession.selectList(command.getName(), param, rowBounds);
} else {
result = sqlSession.selectList(command.getName(), param);
}
.....
return result;
}
会根据不同的类型来执行不同的处理sql方法,这里以executeForMany为入口分析,调用了sqlSessionTemplate的selectList方法。如下:
SqlSessionTemplate
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
return this.sqlSessionProxy.selectList(statement, parameter, rowBounds);
}
sqlSessionProxy是什么东西?
其实这是一个SqlSession的代理类,主要作用是执行具体sql之前先opensession获取一个sqlsession,sql执行完后再closesession。
具体代码如下:
SqlSessionTemplate
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
PersistenceExceptionTranslator exceptionTranslator) {
notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
notNull(executorType, "Property 'executorType' is required");
this.sqlSessionFactory = sqlSessionFactory;
this.executorType = executorType;
this.exceptionTranslator = exceptionTranslator;
// 创建sqlSession动态代理
this.sqlSessionProxy = (SqlSession) newProxyInstance(SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class }, new SqlSessionInterceptor());
}
// 动态代理拦截方法
private class SqlSessionInterceptor implements InvocationHandler {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// 先获取sqlsession,里面就是调用了SqlSessionFactory的openSession方法。
SqlSession sqlSession = getSqlSession(SqlSessionTemplate.this.sqlSessionFactory,
SqlSessionTemplate.this.executorType, SqlSessionTemplate.this.exceptionTranslator);
try {
// 调用SqlSession具体的方法
Object result = method.invoke(sqlSession, args);
if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
// force commit even on non-dirty sessions because some databases require
// a commit/rollback before calling close()
sqlSession.commit(true);
}
return result;
} catch (Throwable t) {
Throwable unwrapped = unwrapThrowable(t);
if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
// release the connection to avoid a deadlock if the translator is no loaded. See issue #22
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
sqlSession = null;
Throwable translated = SqlSessionTemplate.this.exceptionTranslator
.translateExceptionIfPossible((PersistenceException) unwrapped);
if (translated != null) {
unwrapped = translated;
}
}
throw unwrapped;
} finally {
if (sqlSession != null) {
// 收尾工作,管理session
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
}
}
}
}
跟踪的getSqlSession方法,会发现SqlSession的实现类是DefaultSqlSession,它的selectList方法如下
DefaultSqlSession
@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
// 获取xml解析出来的MappedStatement
MappedStatement ms = configuration.getMappedStatement(statement);
// 调用执行器的query方法,这里的Executor默认的是SimpleExecutor
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();
}
}
经过一系列调用最终会调用到如下代码
SimpleExecutor
@Override
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
// 获取Configuration类
Configuration configuration = ms.getConfiguration();
// 创建StatementHandler,默认它的实现类是PreparedStatementHandler,newStatementHandler方法中
// 还会调用interceptorChain.pluginAll给StatementHandler设置拦截器配置,这样后续就可以定义StatementHandler
// 对应的拦截器了。
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
// 最终会执行JDBC中prepare操作
stmt = prepareStatement(handler, ms.getStatementLog());
// 执行查询操作
return handler.query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
// 最终通过数据源获取一个JDBC连接
Connection connection = getConnection(statementLog);
// 最终也会执行JDBC的prepare操作
stmt = handler.prepare(connection, transaction.getTimeout());
// 这里的最终会调用到ParameterHandler的setParameters方法,把mapper方法中的参数转换后,传入
// JDBC的statement中。
handler.parameterize(stmt);
return stmt;
}
继续看query方法,这里的handler是PreparedStatementHandler
如下:
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
// jdbc具体执行方法
ps.execute();
// 调用ResultSethandler进行查询结果数据处理,主要做数据对象映射,然后把处理后的数据返回。
return resultSetHandler.handleResultSets(ps);
}
@Override
public void parameterize(Statement statement) throws SQLException {
// 这个就是上面提到的,“把mapper方法中的参数转换后,传入
// JDBC的statement中”
parameterHandler.setParameters((PreparedStatement) statement);
}