MyBatis源碼解析1-全局熟悉源碼

1.主要的類

下面以org.apache.ibatis.binding.MapperProxy這個類爲主線進行初步探索。

重要的類MapperFactoryBean和兩個InvocationHandler的實現類MapperProxy和SqlSessionInterceptor

還有一些PooledDataSource裏面的InvocationHandler

可以在MyBatis源碼裏搜索"InvocationHandler"，立即可以搜索到所有到類.

org.mybatis.spring.mapper.MapperFactoryBean

package org.mybatis.spring.mapper;

import static org.springframework.util.Assert.notNull;

import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.session.Configuration;
import org.mybatis.spring.SqlSessionTemplate;
import org.mybatis.spring.support.SqlSessionDaoSupport;
import org.springframework.beans.factory.FactoryBean;

/**
 * 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 
  }
  
  public MapperFactoryBean(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  /**
   * {@inheritDoc}
   */
  @Override
  protected void checkDaoConfig() {
    super.checkDaoConfig();

    notNull(this.mapperInterface, "Property 'mapperInterface' is required");

    Configuration configuration = getSqlSession().getConfiguration();
    if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
      try {
        configuration.addMapper(this.mapperInterface);
      } catch (Exception e) {
        logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e);
        throw new IllegalArgumentException(e);
      } finally {
        ErrorContext.instance().reset();
      }
    }
  }

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

  /**
   * {@inheritDoc}
   */
  @Override
  public Class<T> getObjectType() {
    return this.mapperInterface;
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public boolean isSingleton() {
    return true;
  }

  //------------- mutators --------------

  /**
   * Sets the mapper interface of the MyBatis mapper
   *
   * @param mapperInterface class of the interface
   */
  public void setMapperInterface(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  /**
   * Return the mapper interface of the MyBatis mapper
   *
   * @return class of the interface
   */
  public Class<T> getMapperInterface() {
    return mapperInterface;
  }

  /**
   * If addToConfig is false the mapper will not be added to MyBatis. This means
   * it must have been included in mybatis-config.xml.
   * <p/>
   * If it is true, the mapper will be added to MyBatis in the case it is not already
   * registered.
   * <p/>
   * By default addToCofig is true.
   *
   * @param addToConfig
   */
  public void setAddToConfig(boolean addToConfig) {
    this.addToConfig = addToConfig;
  }

  /**
   * Return the flag for addition into MyBatis config.
   *
   * @return true if the mapper will be added to MyBatis in the case it is not already
   * registered.
   */
  public boolean isAddToConfig() {
    return addToConfig;
  }
}

主要方法是

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

重要的InvocationHandler–MapperProxy

public class MapperProxy<T> implements InvocationHandler, Serializable {

  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache;

  public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> 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);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }
}

主要是

return mapperMethod.execute(sqlSession, args);

創建MapperProxy

SqlSessionTemplate.java

  @Override
  public <E> List<E> selectList(String statement, Object parameter) {
    return this.sqlSessionProxy.<E> selectList(statement, parameter);
  }

org.mybatis.spring.SqlSessionTemplate

private class SqlSessionInterceptor implements InvocationHandler {
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      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) {
          // 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) {
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
        }
      }
    }
  }
  

主要通過下面的代碼。就執行了sql語句，獲取到操作數據庫到結果

SqlSession sqlSession = getSqlSession(
          SqlSessionTemplate.this.sqlSessionFactory,
          SqlSessionTemplate.this.executorType,
          SqlSessionTemplate.this.exceptionTranslator);
      try {
        Object result = method.invoke(sqlSession, args);

org.mybatis.spring.SqlSessionTemplate到構造方法裏
新建了一個Proxy代理

======
下面是程序執行流程分析

Spring容器啓動過程中，會發生

Step1: SqlSessionFactoryBean.getObject()

  @Override
  public SqlSessionFactory getObject() throws Exception {
    if (this.sqlSessionFactory == null) {
      afterPropertiesSet();
    }

    return this.sqlSessionFactory;
  }
  

  @Override
  public void afterPropertiesSet() throws Exception {
    notNull(dataSource, "Property 'dataSource' is required");
    notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
    state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
              "Property 'configuration' and 'configLocation' can not specified with together");

    this.sqlSessionFactory = buildSqlSessionFactory();
  }

SqlSessionFactoryBean.buildSqlSessionFactory()
具體包含下面這些子步驟
初始化typeAlias

if (hasLength(this.typeAliasesPackage)) {
      String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,
          ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
      for (String packageToScan : typeAliasPackageArray) {
        configuration.getTypeAliasRegistry().registerAliases(packageToScan,
                typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");
        }
      }
    }
    

創建事務工廠

    if (this.transactionFactory == null) {
      this.transactionFactory = new SpringManagedTransactionFactory();
    }
    

解析Mapping xml文件

          XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
              configuration, mapperLocation.toString(), configuration.getSqlFragments());
          xmlMapperBuilder.parse();

Step2 mapperRegistry.addMapper(type)

  public <T> void addMapper(Class<T> type) {
    mapperRegistry.addMapper(type);
  }

由圖可見

    @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()));
        }

        org.apache.ibatis.session.Configuration configuration = this.properties.getConfiguration();
        if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) {
            configuration = new org.apache.ibatis.session.Configuration();
        }

        if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
            Iterator var4 = this.configurationCustomizers.iterator();

            while(var4.hasNext()) {
                ConfigurationCustomizer customizer = (ConfigurationCustomizer)var4.next();
                customizer.customize(configuration);
            }
        }

        factory.setConfiguration(configuration);
        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 (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
            factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
        }

        if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
            factory.setMapperLocations(this.properties.resolveMapperLocations());
        }

        return factory.getObject();
    }
    

2.Spring Boot啓動過程中調用鏈入下

根據IDEA裏的debug–frames可以看出調用鏈(倒着看就行)

MybatisAutoConfiguration#sqlSessionFactory()
SqlSessionFactoryBean#getObject()
SqlSessionFactoryBean#afterPropertiesSet()
SqlSessionFactoryBean#buildSqlSessionFactory()
XMLMapperBuilder#parse()
XMLMapperBuilder#bindMapperForNamespace();
Configuration#addMapper(boundType);
org.apache.ibatis.binding.MapperRegistry#addMapper(Class<T> type)

調用完畢後，
SqlSessionFactoryBean#getObject()
return this.sqlSessionFactory;

3.Sringboot 啓動完畢後，調用mapper中到dao接口的時候。 調用鏈如下

MapperRegistry#getMapper(sql, sqlSession)

  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);
    }
  }
  
MapperProxyFactory#newInstance(SqlSession sqlSession)


  public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }
  
 protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }
  
 MapperProxy是一個InvocationHandler
 MapperProxy.invoke(Object proxy, Method method, Object[] args)

MapperProxy.invoke 最終會被
SqlSessionInterceptor#invoke(Object proxy, Method method, Object[] args)攔截

Object result = method.invoke(sqlSession, args);

這時候result就是數據庫操作的結果。

連載列表
MyBatis源碼解析1-全局熟悉源碼

MyBatis源碼解析2-MapperRegistry

MyBatis源碼解析3-MapperFactoryBean