Spring mybatis源碼篇章-SqlSessionFactoryBean

經過實例結合源碼的方式解讀，其中涉及到的文件來自於筆者的Github畢設項目，引用的jar包爲mybatis-spring-1.3.0.jar

Mybatis

Mybatis是基於ORM(Object relation mapping)思想而開發的框架插件，本質原理用一句筆者的話即是使用了JAVA鏈接數據庫的方式來執行相應的SQL(PreparedStatement)，並在此基礎上提供了豐富的動態SQL配置以及緩存等概念。(後續文章會說起)

其基本上是企業與傳統數據庫(Oracle/Mysql等)交互經常使用的數據庫持久層框架，以JAVA語言來講，其與Spring的搭配使用也是廣爲流傳。

本文將從源碼的角度淺析Mybatis與Spring的親密搭配

範例

筆者本文只關注SqlSessionFactoryBean的配置，樣例以下

<!--數據源，引用common-pool包的數據源類-->
    <bean id="dataSource-mysql" class="org.apache.commons.dbcp.BasicDataSource"> 
        <property name="driverClassName" value="${jdbc.driverClassName}" /> 
        <property name="url" value="${jdbc.url}" /> 
        <property name="username" value="${jdbc.username}" /> 
        <property name="password" value="${jdbc.password}" /> 
        <property name="initialSize" value="1" /> 
        <property name="maxActive" value="20" /> 
    </bean> 

    <!--sqlSessionFactoryBean建立--> 
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> 
        <property name="dataSource" ref="dataSource-mysql" /> 
        <property name="typeAliasesPackage" value="com.du.wx.model" /> 
        <property name="mapperLocations" value="classpath:com/du/wx/resources/mapper/*.xml"/> 
    </bean> 

    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"> 
        <!-- joggle表明接口 --> 
        <property name="basePackage" value="com.du.wx.mapper.joggle" /> 
    </bean>

由上述的配置可知，在配置SqlSessionFactory數據庫會話工廠Bean對象時必須依賴相應的數據源屬性dataSource

SqlSessionFactoryBean

筆者分層次來解析此類

基礎內部屬性

優先觀察SqlSessionFactoryBean的內部屬性，代碼片斷以下

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;

經常使用的屬性以下：

configLocation mybatis主配置文件路徑，支持classpath語法

mapperLocations 指定mybatis的mapper配置文件，支持classpath語法

dataSource 數據源

typeAliasesPackage 指定model層類名的別名掃描包，這與mapper配置中的parameterType和resultType搭配使用

InitializingBean複寫方法

緊接着看下其複寫的afterPropertiesSet()方法，代碼以下

@Override
  public void afterPropertiesSet() throws Exception {
    //datasource not allowed to be null.
    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();
  }

與前文說起的對應，必須確保dataSource屬性已經獲得配置。

實例化步驟

最後查看關鍵實例方法buildSqlSessionFactory()方法，因爲片斷過長，筆者截取幾段來進行講解

---

Mybatis主文件加載

Configuration configuration;

    XMLConfigBuilder xmlConfigBuilder = null;
    if (this.configuration != null) {
      configuration = this.configuration;
      if (configuration.getVariables() == null) {
        configuration.setVariables(this.configurationProperties);
      } else if (this.configurationProperties != null) {
        configuration.getVariables().putAll(this.configurationProperties);
      }
    } else if (this.configLocation != null) {
      //若是spring配置中configLocation屬性不爲空，則加載指定的Mybatis配置
      xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
      configuration = xmlConfigBuilder.getConfiguration();
    } else {
      //不然則採用默認的Mybatis配置，@see Configuration
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Property `configuration` or 'configLocation' not specified, using default MyBatis Configuration");
      }
      configuration = new Configuration();
      configuration.setVariables(this.configurationProperties);
    }

經過上述配置代表，內部屬性configLocation是非必須配置項

---

model別名映射掃描

if (hasLength(this.typeAliasesPackage)) {
      //截取typeAliasesPackage屬性的包，支持,或;
      String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
      for (String packageToScan : typeAliasPackageArray) {
        //對應方法的目的是經過掃描包獲得其包以及子包目錄下的全部Class，而後爲每一個class註冊別名  
        configuration.getTypeAliasRegistry().registerAliases(packageToScan,
        typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");
        }
      }
    }

即對內部屬性typeAliasesPackage支持,;做爲分隔符以加載多個目錄，主要是爲了方便編程人員使用parameterType/resultType等屬性

---

mapper配置文件加載

if (!isEmpty(this.mapperLocations)) {
      //mapperLocations
      for (Resource mapperLocation : this.mapperLocations) {
        if (mapperLocation == null) {
          continue;
        }

        try {
          //對掃描的每一個配置文件進行解析，並保存其中的必要參數，後續會分析
          XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
              configuration, mapperLocation.toString(), configuration.getSqlFragments());
          xmlMapperBuilder.parse();
        } catch (Exception e) {
          throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
        } finally {
          ErrorContext.instance().reset();
        }

        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");
        }
      }
    } else {
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");
      }
    }

關鍵處理XML配置的mapper文件，用到了mybatis包中的org.apache.ibatis.builder.xml.XMLMapperBuilder類進行解析。這個後續分析

---

Configuration-全部關於Mybatis的信息均存儲在Mybatis包中的org.apache.ibatis.session.Configuration類上

return this.sqlSessionFactoryBuilder.build(configuration);

Spring呢，就經過SqlSessionFactoryBuilder類來建立相應的SqlSessionFactory對象。具體的因爲篇幅過長，就放在後文分析。

總結

從上文即可以看出來Spring框架是如何整合Mybatis的，就是這個Mybatis的關鍵類Configuration。而相應的開關數據庫等一系列的功能都是經過Spring的SqlSessionFactory對象來操控的。這也是二者結合最核心的地方