上篇文章《深入淺出Mybatis系列(一)---Mybatis入門》, 寫了一個Demo簡單體現了一下Mybatis的流程。在這次,將簡單介紹一下Mybatis的設定檔:
上次範例中,我們以 SqlSessionFactoryBuilder 去創建SqlSessionFactory, 那麼,我們就先從SqlSessionFactoryBuilder入手, 咱們先看看源碼是怎麼實現的:
SqlSessionFactoryBuilder原始碼片段:
1 public class SqlSessionFactoryBuilder { 2 3 //Reader读取mybatis配置文件,传入构造方法 4 //除了Reader外,其实还有对应的inputStream作为参数的构造方法, 5 //这也体现了mybatis配置的灵活性 6 public SqlSessionFactory build(Reader reader) { 7 return build(reader, null, null); 8 } 9 10 public SqlSessionFactory build(Reader reader, String environment) { 11 return build(reader, environment, null); 12 } 13 14 //mybatis配置文件 + properties, 此时mybatis配置文件中可以不配置properties,也能使用${}形式 15 public SqlSessionFactory build(Reader reader, Properties properties) { 16 return build(reader, null, properties); 17 } 18 19 //通过XMLConfigBuilder解析mybatis配置,然后创建SqlSessionFactory对象 20 public SqlSessionFactory build(Reader reader, String environment, Properties properties) { 21 try { 22 XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties); 23 //下面看看这个方法的源码 24 return build(parser.parse()); 25 } catch (Exception e) { 26 throw ExceptionFactory.wrapException("Error building SqlSession.", e); 27 } finally { 28 ErrorContext.instance().reset(); 29 try { 30 reader.close(); 31 } catch (IOException e) { 32 // Intentionally ignore. Prefer previous error. 33 } 34 } 35 } 36 37 public SqlSessionFactory build(Configuration config) { 38 return new DefaultSqlSessionFactory(config); 39 } 40 41 }
透過原始碼,我們可以看到SqlSessionFactoryBuilder 透過XMLConfigBuilder 去解析我們傳入的mybatis的設定文件, 下面就接著看看 XMLConfigBuilder 部分原始碼:
1 /** 2 * mybatis 配置文件解析 3 */ 4 public class XMLConfigBuilder extends BaseBuilder { 5 public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) { 6 this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props); 7 } 8 9 private XMLConfigBuilder(XPathParser parser, String environment, Properties props) { 10 super(new Configuration()); 11 ErrorContext.instance().resource("SQL Mapper Configuration"); 12 this.configuration.setVariables(props); 13 this.parsed = false; 14 this.environment = environment; 15 this.parser = parser; 16 } 17 18 //外部调用此方法对mybatis配置文件进行解析 19 public Configuration parse() { 20 if (parsed) { 21 throw new BuilderException("Each XMLConfigBuilder can only be used once."); 22 } 23 parsed = true; 24 //从根节点configuration 25 parseConfiguration(parser.evalNode("/configuration")); 26 return configuration; 27 } 28 29 //此方法就是解析configuration节点下的子节点 30 //由此也可看出,我们在configuration下面能配置的节点为以下10个节点 31 private void parseConfiguration(XNode root) { 32 try { 33 propertiesElement(root.evalNode("properties")); //issue #117 read properties first 34 typeAliasesElement(root.evalNode("typeAliases")); 35 pluginElement(root.evalNode("plugins")); 36 objectFactoryElement(root.evalNode("objectFactory")); 37 objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); 38 settingsElement(root.evalNode("settings")); 39 environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631 40 databaseIdProviderElement(root.evalNode("databaseIdProvider")); 41 typeHandlerElement(root.evalNode("typeHandlers")); 42 mapperElement(root.evalNode("mappers")); 43 } catch (Exception e) { 44 throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e); 45 } 46 } 47 }
#透過以上原始碼,我們就能看出,在mybatis的設定檔中:
1. configuration節點為根節點。
2. 在configuration節點下,我們可以設定10個子節點, 分別為:properties、typeAliases、plugins、objectFactory、objectWrapperFactory、settings、environments、databaseIdProvider、typeHandlers、mappers。
本篇文章就先只介紹這些內容,接下來的文章將依序分析解析這個10個節點中比較重要的幾個節點的源碼,看看在解析這些節點的時候,到底做了些什麼。
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