mybatis源码解析2---XMLConfigBuilder解析

1.XMLConfigBuilder

XMLConfigBuilder类位于Mybatis包的org.apache.ibatis.builder.xml目录下，继承于BaseBuilder类，关于BaseBuilder类后续再看。

XMLConfigBuilder看名字能猜到是关于mybatis的XML配置的构造类，负责构造mybatis的XML配置的。

XMLConfigBuilder共有四个属性，代码如下：

1 private boolean parsed;//解析标识,因为Configuration是全局变量，只需要解析创建一次即可，true表示已经解析创建过,false则表示没有
2 private XPathParser parser;
3 private String environment;//环境参数
4 private ReflectorFactory localReflectorFactory = new DefaultReflectorFactory();

XMLConfigBuilder共有6个public构造方法和一个private的构造方法，如下：

 1  public XMLConfigBuilder(Reader reader) {
 2     this(reader, null, null);
 3   }
 4 
 5   public XMLConfigBuilder(Reader reader, String environment) {
 6     this(reader, environment, null);
 7   }
 8 
 9   public XMLConfigBuilder(Reader reader, String environment, Properties props) {
10     this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
11   }
12 
13   public XMLConfigBuilder(InputStream inputStream) {
14     this(inputStream, null, null);
15   }
16 
17   public XMLConfigBuilder(InputStream inputStream, String environment) {
18     this(inputStream, environment, null);
19   }
20 
21   public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
22     this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
23   }
24 
25   private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
26     super(new Configuration());//调用父类的构造方法
27     ErrorContext.instance().resource("SQL Mapper Configuration");
28     this.configuration.setVariables(props);
29     this.parsed = false;
30     this.environment = environment;
31     this.parser = parser;
32   }

很显然6个public的构造方法都是根据mybatis的配置文件流创建一个XPathParser对象，然后最终都调用了私有的构造方法，而私有的构造方法先是调用了父类BaseBuilder的构造方法，然后分别根据参数给四个属性赋值。

而上一篇文章提到了SqlSessionFactoryBuilder中是通过创建一个XMLConfigBuilder对象，然后调用了对象的parse()方法获取到一个Configuration对象。接下来就先看看XMLConfigBuilder的parse方法，如下：、

 1 public Configuration parse() {
 2     if (parsed) {//判断Configuration是否解析过，Configuration是全局变量，只需要解析创建一次即可
 3       throw new BuilderException("Each XMLConfigBuilder can only be used once.");
 4     }
 5     parsed = true;
 6     parseConfiguration(parser.evalNode("/configuration"));//调用下面的方法,parser.evalNode("/configuration")解析XML配置的configuration节点的内容，得到XNode对象
 7     return configuration;
 8   }
 9   //根据root中存储的是configuration节点的内容
10   private void parseConfiguration(XNode root) {
11     try {
12       Properties settings = settingsAsPropertiess(root.evalNode("settings"));//设置settings配置
13       //issue #117 read properties first
14       propertiesElement(root.evalNode("properties"));//设置properties配置
15       loadCustomVfs(settings);
16       typeAliasesElement(root.evalNode("typeAliases"));//设置typeAliases配置
17       pluginElement(root.evalNode("plugins"));//设置plugins配置
18       objectFactoryElement(root.evalNode("objectFactory"));//设置objectFactory配置
19       objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));//设置objectWrapperFactory配置
20       reflectorFactoryElement(root.evalNode("reflectorFactory"));//设置reflectFactory配置
21       settingsElement(settings);
22       // read it after objectFactory and objectWrapperFactory issue #631
23       environmentsElement(root.evalNode("environments"));//设置environments配置
24       databaseIdProviderElement(root.evalNode("databaseIdProvider"));//设置databaseIdProvider配置
25       typeHandlerElement(root.evalNode("typeHandlers"));//设置typeHandlers配置
26       mapperElement(root.evalNode("mappers"));//设置mappers配置
27     } catch (Exception e) {
28       throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
29     }
30   }

可以看出parse的作用是解析mybatis-config.xml的configuration节点的内容，然后挨个赋值给configuration对象的属性；

而XMLConfigBuilder的其他私有方法都是给根据XNode对象（XML配置的configuration节点内容）来给全局配置变量configuration的属性进行赋值，关于Configuration类的解析下一章会解析

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mybatis源码解析2---XMLConfigBuilder解析

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