spring如何管理mybatis(一) ----- 动态代理接口

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问题来源

最近在集成spring和mybatis时遇到了很多问题，从网上查了也解决了，但是就是心里有点别扭，想看看到底怎么回事，所以跟了下源码，终于发现了其中的奥妙。

问题分析

首先我们来看看基本的配置。

spring的配置：

<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource">
<property name="driverClassName" value="${db.driver}"/>
<property name="url" value="${db.url}"/>
<property name="username" value="${db.userName}"/>
<property name="password" value="${db.password}"/>
<property name="maxActive" value="${druid.maxActive}"></property>
<property name="maxWait" value="${druid.maxWait}"></property>
</bean> <bean id="mSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">

<property name="dataSource" ref="dataSource"/>

<property name="mapperLocations" value="classpath*:mapper/*.xml"/>
</bean>



<bean id="mapperScannerConfigurer" class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.zex.dao" />
<property name="sqlSessionFactoryBeanName" value="mSqlSessionFactory"></property>
</bean>

<bean id="transactionManagermeta"
class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dataSource"/>
</bean>

<tx:annotation-driven/>

mapper文件和dao接口

controller层代码

源码跟踪

首先我们分解下spring-mybatis配置信息，数据库配置不说了，我们来看看sqlSessionFactory的配置

这个配置，主要是把SqlSessionFactoryBean用spring管理起来了，我们一起来看看这个bean的作用

/**
* {@code FactoryBean} that creates an MyBatis {@code SqlSessionFactory}.
* This is the usual way to set up a shared MyBatis {@code SqlSessionFactory} in a Spring application context;
* the SqlSessionFactory can then be passed to MyBatis-based DAOs via dependency injection.
*
* Either {@code DataSourceTransactionManager} or {@code JtaTransactionManager} can be used for transaction
* demarcation in combination with a {@code SqlSessionFactory}. JTA should be used for transactions
* which span multiple databases or when container managed transactions (CMT) are being used.
*/

这是这个类的注释：这个类主要用来创建Mybatis需要的SqlSessionFactory,在spring的上下文共享这个类。这里可以看出这个类用来

管理mybatis的配置信息，讲mybatis的信息管理载spring中，我们看下基本属性。

public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>, InitializingBean, ApplicationListener<ApplicationEvent> { private static final Log LOGGER = LogFactory.getLog(SqlSessionFactoryBean.class); private Resource configLocation; private Configuration configuration; private Resource[] mapperLocations; private DataSource dataSource; private TransactionFactory transactionFactory; private Properties configurationProperties; private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder(); private SqlSessionFactory sqlSessionFactory; //EnvironmentAware requires spring 3.1
private String environment = SqlSessionFactoryBean.class.getSimpleName(); private boolean failFast; private Interceptor[] plugins; private TypeHandler<?>[] typeHandlers; private String typeHandlersPackage; private Class<?>[] typeAliases; private String typeAliasesPackage; private Class<?> typeAliasesSuperType; //issue #19. No default provider.
private DatabaseIdProvider databaseIdProvider; private Class<? extends VFS> vfs; private Cache cache; private ObjectFactory objectFactory; private ObjectWrapperFactory objectWrapperFactory;
}

这里我们看到了有个

private Resource configLocation;

这个属性用来管理mybatis基本配置信息的xml的位置，sqlSessionFactoryBean会根据这个配置加载Configuration,当然我们也可以通过这个类中

其他的参数来配置，例如typeHandler，typeAliasesPackages等等，这些既可以在Configuration的xml中配置，也可以直接配置。所以这个bean主要作用就是生成configuration，

然后通过sqlSessionFactoryBuilder来创建sqlSessionFactory，可以说最重要的就是创建这个sqlSessionFactory。

接下来我们看看SqlSessionTemplate

SqlSessionTemplate这个类实现了mybatis的sqlSession，mybatis的sqlSession主要是执行数据库操作，spring实现了SqlSessionTemplate这个类，主要是讲mybatis对数据库的
操作转嫁到spring中来，让spring来进行数据的操作。我们看看这个类的属性。

public class SqlSessionTemplate implements SqlSession { private final SqlSessionFactory sqlSessionFactory; private final ExecutorType executorType; private final SqlSession sqlSessionProxy; private final PersistenceExceptionTranslator exceptionTranslator; /**
* Constructs a Spring managed SqlSession with the {@code SqlSessionFactory}
* provided as an argument.
*
* @param sqlSessionFactory
*/
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());
} /**
* Constructs a Spring managed SqlSession with the {@code SqlSessionFactory}
* provided as an argument and the given {@code ExecutorType}
* {@code ExecutorType} cannot be changed once the {@code SqlSessionTemplate}
* is constructed.
*
* @param sqlSessionFactory
* @param executorType
*/
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) {
this(sqlSessionFactory, executorType,
new MyBatisExceptionTranslator(
sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(), true));
} /**
* Constructs a Spring managed {@code SqlSession} with the given
* {@code SqlSessionFactory} and {@code ExecutorType}.
* A custom {@code SQLExceptionTranslator} can be provided as an
* argument so any {@code PersistenceException} thrown by MyBatis
* can be custom translated to a {@code RuntimeException}
* The {@code SQLExceptionTranslator} can also be null and thus no
* exception translation will be done and MyBatis exceptions will be
* thrown
*
* @param sqlSessionFactory
* @param executorType
* @param exceptionTranslator
*/
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;
this.sqlSessionProxy = (SqlSession) newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class },
new SqlSessionInterceptor());
}

这个类包含有四个基本的属性，其中的SqlSessionFactory就是我们之前通过SqlSessionFactoryBean生成的那个SqlSessionFactory，他的作用是提供Configation,

另一个重要的属性就是SqlSessionProxy这个类其实是个代理类，代理的Mybatis的sqlSession接口，这样他就可以拥有MyBatis的sqlSession的所有方法了。这个代理类在执行的时候

其实是走的

SqlSessionInterceptor的invoke方法

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
final SqlSession sqlSession = getSqlSession(
SqlSessionTemplate.this.sqlSessionFactory,
SqlSessionTemplate.this.executorType,
SqlSessionTemplate.this.exceptionTranslator);
try {
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) {
Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
if (translated != null) {
unwrapped = translated;
}
}
throw unwrapped;
} finally {
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
}
}

这个方法就是获取真实的sqlSession然后调用数据库的操作。

ok，以上就是spring和mybatis的整合点，接下来我们看看是如何只通过一个接口就能操作数据库的，肯定用的是代理模式，只是mybatis用的太好了。

首先我们来看个类，MapperFactoryBean

/**
* BeanFactory that enables injection of MyBatis mapper interfaces. It can be set up with a
* SqlSessionFactory or a pre-configured SqlSessionTemplate.
* <p>
* Sample configuration:
*
* <pre class="code">
* {@code
* <bean id="baseMapper" class="org.mybatis.spring.mapper.MapperFactoryBean" abstract="true" lazy-init="true">
* <property name="sqlSessionFactory" ref="sqlSessionFactory" />
* </bean>
*
* <bean id="oneMapper" parent="baseMapper">
* <property name="mapperInterface" value="my.package.MyMapperInterface" />
* </bean>
*
* <bean id="anotherMapper" parent="baseMapper">
* <property name="mapperInterface" value="my.package.MyAnotherMapperInterface" />
* </bean>
* }
* </pre>
* <p>
* Note that this factory can only inject <em>interfaces</em>, not concrete classes.
*
* @author Eduardo Macarron
*
* @see SqlSessionTemplate
*/
public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> { private Class<T> mapperInterface; private boolean addToConfig = true; public MapperFactoryBean() {
//intentionally empty
}/**
* {@inheritDoc}
*/
@Override
public T getObject() throws Exception {
return getSqlSession().getMapper(this.mapperInterface);
}}

这个类就是可以注入mapper接口的工厂类，可以理解为他可以通过接口生产一个代理类用来调用接口的工作，首先他是个FactoryBean可以通过getObject(),获取到他管理的bean，

这个类最主要的就是传入一个sqlSessionFactory。

我们先来看看一般的用法

我们看到将这个类由spring管理，然后注入sqlSessionFactory，然后又用其他的类去继承它并注入接口，这样这个接口就被管理起来了，生成了代理类。我们在获取这个接口的时候得到的其实就是代理类。不过这样子有点麻烦，我们每次都要进行接口的配置，所以spring提供了org.mybatis.spring.mapper.MapperScannerConfigurer这个类来管理所有的接口了，这个类会所有所有的配置的包中的接口，然后将每个接口的定义设置好生成代理相应的信息。

@Override
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages); if (beanDefinitions.isEmpty()) {
logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
} else {
for (BeanDefinitionHolder holder : beanDefinitions) {
GenericBeanDefinition definition = (GenericBeanDefinition) holder.getBeanDefinition(); if (logger.isDebugEnabled()) {
logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName()
+ "' and '" + definition.getBeanClassName() + "' mapperInterface");
} // the mapper interface is the original class of the bean
// but, the actual class of the bean is MapperFactoryBean
definition.getPropertyValues().add("mapperInterface", definition.getBeanClassName());
definition.setBeanClass(MapperFactoryBean.class); definition.getPropertyValues().add("addToConfig", this.addToConfig); boolean explicitFactoryUsed = false;
if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionFactory != null) {
definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
explicitFactoryUsed = true;
} if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
if (explicitFactoryUsed) {
logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionTemplate != null) {
if (explicitFactoryUsed) {
logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
explicitFactoryUsed = true;
} if (!explicitFactoryUsed) {
if (logger.isDebugEnabled()) {
logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
}
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
}
}
} return beanDefinitions;
}

我们重点看下

definition.getPropertyValues().add("mapperInterface", definition.getBeanClassName());
definition.setBeanClass(MapperFactoryBean.class);
definition.getPropertyValues().add("addToConfig", this.addToConfig);

这三行代码，指定了mapper接口的类型--MapperFactoryBean,以及相应的接口信息，这样bean的定义就指定了必要的信息，当spring创建这个mapper接口对应的bean的时候就会生成相应的MapperFactoryBean类，当需要接口实例时就会调用MapperFactoryBean的getObject（）方法获取相应的bean。

@Override
public T getObject() throws Exception {
return getSqlSession().getMapper(this.mapperInterface);
}

这个方法就是获取mapper接口对应的代理类，这个方法给我们上了一堂如何完美利用jdk代理类的课。建议大家可以研究下。这里不是我们的重点，就不带大家研读了。