MyBatis架構中Mapper映射配置的使用及原理解析(二) 配置篇 SqlSessionFactoryBuilder，XMLConfigBuilder

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在 <MyBatis架構中Mapper映射配置的使用及原理解析(一) 配置與使用> 的demo中看到了SessionFactory的建立過程：

SqlSessionFactory sessionFactory = null;        String resource = "mybatisConfig.xml";        try {            sessionFactory = new SqlSessionFactoryBuilder().build(Resources                    .getResourceAsReader(resource));        } catch (IOException e) {            e.printStackTrace();        }

那麼我們就從SqlSessionFactoryBuilder開始，看看Mybatis的載入過程。

SqlSessionFactoryBuilder的核心源碼：

package org.apache.ibatis.session;

public class SqlSessionFactoryBuilder {

//通過Reader讀取Mybatis配置

 public SqlSessionFactory build(Reader reader, String environment, Properties properties) {

    try {            XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);      return build(parser.parse()); //parse()方法得到Configuration    } catch (Exception e) {      throw ExceptionFactory.wrapException("Error building SqlSession.", e);    } finally {      ErrorContext.instance().reset();      try {        reader.close();      } catch (IOException e) {        // Intentionally ignore. Prefer previous error.      }    }  }
  //通過InputStream讀取Mybatis配置  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {    try {      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);      return build(parser.parse()); //parse()方法得到Configuration    } 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.      }    }  }  
  //以上2個方法最終調用的是build(Configuration config)  public SqlSessionFactory build(Configuration config) {    return new DefaultSqlSessionFactory(config);  }}

通過源碼，我們可以看到SqlSessionFactoryBuilder 通過XMLConfigBuilder 去解析我們傳入的mybatis的設定檔，構造出Configuration，最終返回new DefaultSqlSessionFactory(config)的SqlSessionFactory執行個體。

接下來我們看看 XMLConfigBuilder 是怎樣解析Mybatis的設定檔的，下面是部分源碼：

 

package org.apache.ibatis.builder.xml;/** * 解析Mybatis設定檔 */public class XMLConfigBuilder extends BaseBuilder {  private boolean parsed;  private XPathParser parser;  private String environment;  public XMLConfigBuilder(Reader reader) {    this(reader, null, null);  }  public XMLConfigBuilder(Reader reader, String environment) {    this(reader, environment, null);  }  public XMLConfigBuilder(Reader reader, String environment, Properties props) {    this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);  }  public XMLConfigBuilder(InputStream inputStream) {    this(inputStream, null, null);  }  public XMLConfigBuilder(InputStream inputStream, String environment) {    this(inputStream, environment, null);  }  public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {    this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);  }  private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {    super(new Configuration());    ErrorContext.instance().resource("SQL Mapper Configuration");    this.configuration.setVariables(props);    this.parsed = false;    this.environment = environment;    this.parser = parser;  }  //調用此方法對mybatis設定檔進行解析,返回Configuration對象  public Configuration parse() {    if (parsed) {      throw new BuilderException("Each XMLConfigBuilder can only be used once.");    }    parsed = true;    //從根節點configuration，開始解析    parseConfiguration(parser.evalNode("/configuration"));    return configuration;  }    //解析configuration節點下的10個子節點。  private void parseConfiguration(XNode root) {    try {      propertiesElement(root.evalNode("properties")); //issue #117 read properties first      typeAliasesElement(root.evalNode("typeAliases"));      pluginElement(root.evalNode("plugins"));      objectFactoryElement(root.evalNode("objectFactory"));      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));      settingsElement(root.evalNode("settings"));      environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631      databaseIdProviderElement(root.evalNode("databaseIdProvider"));      typeHandlerElement(root.evalNode("typeHandlers"));      mapperElement(root.evalNode("mappers"));    } catch (Exception e) {      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);    }  }  }  

 從上面可以看出可以配置10個子節點， 分別為：properties、typeAliases、plugins、objectFactory、objectWrapperFactory、settings、environments、databaseIdProvider、typeHandlers、mappers。

MyBatis架構中Mapper映射配置的使用及原理解析(二) 配置篇 SqlSessionFactoryBuilder，XMLConfigBuilder