× configuration 配置

   × properties 屬性
   × settings 設(shè)置
   × typeAliases 類型命名
   × typeHandlers 類型處理器
   × objectFactory 對象工廠
   × plugins 插件
   × environments 環(huán)境
       × environment 環(huán)境變量
       × transactionManager 事務(wù)管理器
       × dataSource 數(shù)據(jù)源
× 映射器

String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
// 1、Mybatis初始化(根據(jù)InputStream得到SqlSessionFactory)
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 2、創(chuàng)建SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
// 3、執(zhí)行SQL語句并返回結(jié)果
List list = sqlSession.selectList("com.foo.bean.BlogMapper.queryAllBlogInfo");

SqlSessionFactory sqlSessionFactory =
    new SqlSessionFactoryBuilder().build(inputStream);

// mybatis初始化第一步，調(diào)用build()，上圖中的1
build(inputStream) 調(diào)用 build(inputStream,null,null) 

// mybatis初始化第二步，手動創(chuàng)建XMLConfigBuilder，上圖中的2 
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, null,null);

// mybatis初始化第三步，parse()方法構(gòu)建configuration對象的過程，上圖中的 3 和 4
Configuration configuration=parser.parse();   

// mybatis初始化第四步，使用Configuration對象創(chuàng)建SqlSessionFactory 上圖中 5
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);

SqlSessionFactoryBuilder.java

public SqlSessionFactory build(InputStream inputStream)
{   //1. 調(diào)用SqlSessionFactoryBuilder對象的build(inputStream)方法
    return build(inputStream, null, null);
}
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties)
{
    try
    {
        //2. 創(chuàng)建XMLConfigBuilder對象用來解析XML配置文件，生成Configuration對象
        XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
        //3. 將XML配置文件內(nèi)的信息解析成Java對象Configuration對象
        Configuration config = parser.parse();
        //4. 根據(jù)Configuration對象創(chuàng)建出SqlSessionFactory對象
        return build(config);
    }
    catch (Exception e)
    {
        throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    }
    finally
    {
        ErrorContext.instance().reset();
        try
        {
            inputStream.close();
        }
        catch (IOException e)
        {
            // Intentionally ignore. Prefer previous error.
        }
    }
}
//從此處可以看出，MyBatis內(nèi)部通過Configuration對象來創(chuàng)建SqlSessionFactory,用戶也可以自己通過API構(gòu)造好Configuration對象，調(diào)用此方法創(chuàng)建SqlSessionFactory
public SqlSessionFactory build(Configuration config)
{
    return new DefaultSqlSessionFactory(config);
}

    public Configuration parse()
    {
        if (parsed)
        {
            throw new BuilderException("Each XMLConfigBuilder can only be used once.");
        }
        parsed = true;
        //源碼中沒有這一句，只有 parseConfiguration(parser.evalNode("/configuration"));
        //為了讓讀者看得更明晰，源碼拆分為以下兩句
        XNode configurationNode = parser.evalNode("/configuration");
        parseConfiguration(configurationNode);
        return configuration;
    }
    /*
    解析 "/configuration"節(jié)點(diǎn)下的子節(jié)點(diǎn)信息，然后將解析的結(jié)果設(shè)置到Configuration對象中
    */
  private void parseConfiguration(XNode root) {
    try {
      //1.首先處理properties 節(jié)點(diǎn)	
      propertiesElement(root.evalNode("properties")); 
      //issue #117 read properties first
      //2.處理typeAliases
      typeAliasesElement(root.evalNode("typeAliases"));
      //3.處理插件
      pluginElement(root.evalNode("plugins"));
      //4.處理objectFactory
      objectFactoryElement(root.evalNode("objectFactory"));
      //5.objectWrapperFactory
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      //6.settings
      settingsElement(root.evalNode("settings"));
      //7.處理environments
      environmentsElement(root.evalNode("environments")); 
      // read it after objectFactory and objectWrapperFactory issue #631
      //8.database
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      //9. typeHandlers
      typeHandlerElement(root.evalNode("typeHandlers"));
      //10 mappers
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }

/*
   解析environments節(jié)點(diǎn)，并將結(jié)果設(shè)置到Configuration對象中
   注意：創(chuàng)建envronment時，如果SqlSessionFactoryBuilder指定了特定的環(huán)境（即數(shù)據(jù)源）；
         則返回指定環(huán)境（數(shù)據(jù)源）的Environment對象，否則返回默認(rèn)的Environment對象；
         這種方式實(shí)現(xiàn)了MyBatis可以連接多數(shù)據(jù)源
*/
private void environmentsElement(XNode context) throws Exception
{
    if (context != null)
    {
        if (environment == null)
        {
            environment = context.getStringAttribute("default");
        }
        for (XNode child : context.getChildren())
        {
            String id = child.getStringAttribute("id");
            if (isSpecifiedEnvironment(id))
            {
                //1.創(chuàng)建事務(wù)工廠 TransactionFactory，繼續(xù)深入子節(jié)點(diǎn)
                TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
                DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
                //2.創(chuàng)建數(shù)據(jù)源DataSource
                DataSource dataSource = dsFactory.getDataSource();
                //3. 構(gòu)造Environment對象
                Environment.Builder environmentBuilder = new Environment.Builder(id)
                .transactionFactory(txFactory)
                .dataSource(dataSource);
                //4. 將創(chuàng)建的Envronment對象設(shè)置到configuration 對象中
                configuration.setEnvironment(environmentBuilder.build());
            }
        }
    }
}
private boolean isSpecifiedEnvironment(String id)
{
    if (environment == null)
    {
        throw new BuilderException("No environment specified.");
    }
    else if (id == null)
    {
        throw new BuilderException("Environment requires an id attribute.");
    }
    else if (environment.equals(id))
    {
        return true;
    }
    return false;
}

public Configuration parse()
{
    if (parsed)
    {
        throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    //源碼中沒有這一句，只有 parseConfiguration(parser.evalNode("/configuration"));
    //為了讓讀者看得更明晰，源碼拆分為以下兩句
    XNode configurationNode = parser.evalNode("/configuration");
    parseConfiguration(configurationNode);
    return configuration;   // 完成后，返回configuration對象，返回給程序員
}

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);

String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
//手動創(chuàng)建XMLConfigBuilder，并解析創(chuàng)建Configuration對象
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, null,null);
Configuration configuration=parse();
//使用Configuration對象創(chuàng)建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
//使用MyBatis
SqlSession sqlSession = sqlSessionFactory.openSession();
List list = sqlSession.selectList("com.foo.bean.BlogMapper.queryAllBlogInfo");

  private void environmentsElement(XNode context) throws Exception {
    if (context != null) {
      if (environment == null) {
        environment = context.getStringAttribute("default");
      }
      for (XNode child : context.getChildren()) {
        String id = child.getStringAttribute("id");
        //是和默認(rèn)的環(huán)境相同時，解析之
        if (isSpecifiedEnvironment(id)) {
          TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
          DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
          DataSource dataSource = dsFactory.getDataSource();
 
          //使用了Environment內(nèi)置的構(gòu)造器Builder，傳遞id 事務(wù)工廠和數(shù)據(jù)源
          Environment.Builder environmentBuilder = new Environment.Builder(id)
              .transactionFactory(txFactory)
              .dataSource(dataSource);
          configuration.setEnvironment(environmentBuilder.build());
        }
      }
    }
  }

public final class Environment {
  private final String id;
  private final TransactionFactory transactionFactory;
  private final DataSource dataSource;
 
  public Environment(String id, TransactionFactory transactionFactory, DataSource dataSource) {
    if (id == null) {
      throw new IllegalArgumentException("Parameter 'id' must not be null");
    }
    if (transactionFactory == null) {
        throw new IllegalArgumentException("Parameter 'transactionFactory' must not be null");
    }
    this.id = id;
    if (dataSource == null) {
      throw new IllegalArgumentException("Parameter 'dataSource' must not be null");
    }
    this.transactionFactory = transactionFactory;
    this.dataSource = dataSource;
  }
 
  public static class Builder {
      private String id;
      private TransactionFactory transactionFactory;
      private DataSource dataSource;
 
    public Builder(String id) {
      this.id = id;
    }
 
    public Builder transactionFactory(TransactionFactory transactionFactory) {
      this.transactionFactory = transactionFactory;
      return this;
    }
 
    public Builder dataSource(DataSource dataSource) {
      this.dataSource = dataSource;
      return this;
    }
 
    public String id() {
      return this.id;
    }
 
    public Environment build() {
      return new Environment(this.id, this.transactionFactory, this.dataSource);
    }
 
  }
 
  public String getId() {
    return this.id;
  }
 
  public TransactionFactory getTransactionFactory() {
    return this.transactionFactory;
  }
 
  public DataSource getDataSource() {
    return this.dataSource;
  }
 
}