Mybatis配置文件解析（转载）

流程图

demo案例

还是从案例开始。

public static void main(String[] args) {
    String resource = "mybatis-config.xml";
    InputStream inputStream = null;
    SqlSession sqlSession = null;
    try {
        inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = sqlSessionFactory.openSession();

        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        System.out.println(userMapper.selectById(1));

    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            inputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        sqlSession.close();
    }
}

从SqlSessionFactoryBuilder开始。

SqlSessionFactoryBuilder类

org.apache.ibatis.session.SqlSessionFactoryBuilder

该类里全是build方法各种重载。

//这个方法啥也没干  
public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
}

最终来到另外一个build方法里：

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
        //创建一个XMLConfigBuilder对象  
        XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
        return build(parser.parse());
    } 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.
        }
    }
}

XMLConfigBuilder类

该类的构造方法重载：

首先进入：

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;
}

build(parser.parse());中的parser.parse()；

mybatis-config.xml在哪里解析的呢？

请看下面这个方法：

//该方法返回一个Configuration对象
public Configuration parse() {
  if (parsed) {
    throw new BuilderException("Each XMLConfigBuilder can only be used once.");
  }
  parsed = true;
  //关键点
  parseConfiguration(parser.evalNode("/configuration"));
  return configuration;
}

parseConfiguration(parser.evalNode("/configuration"));

终于看到开始解析配置文件了：

进入方法parseConfiguration。

private void parseConfiguration(XNode root) {
    try {
        //issue #117 read properties first
        propertiesElement(root.evalNode("properties"));
        Properties settings = settingsAsProperties(root.evalNode("settings"));
        loadCustomVfs(settings);
        loadCustomLogImpl(settings);
        typeAliasesElement(root.evalNode("typeAliases"));
        pluginElement(root.evalNode("plugins"));
        objectFactoryElement(root.evalNode("objectFactory"));
        objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
        reflectorFactoryElement(root.evalNode("reflectorFactory"));
        settingsElement(settings);
        // read it after objectFactory and objectWrapperFactory issue #631
        environmentsElement(root.evalNode("environments"));
        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);
    }
}

这里就是把mybatis-config.xml内容解析，然后设置到Configuration对象中。

那么我们定义的Mapper.xml是在哪里解析的呢？

我们的Mapper.xml在mybatis-config.xml中的配置是这样的：

<mapper>使用方式有以下四种：

//1使用类路径
<mappers>
    <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
      <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
</mappers>
//2使用绝对url路径
<mappers>
   <mapper url="file:///var/mappers/AuthorMapper.xml"/>
   <mapper url="file:///var/mappers/BlogMapper.xml"/>
   <mapper url="file:///var/mappers/PostMapper.xml"/>
</mappers>
//3使用java类名
<mappers>
   <mapper class="org.mybatis.builder.AuthorMapper"/>
   <mapper class="org.mybatis.builder.BlogMapper"/>
   <mapper class="org.mybatis.builder.PostMapper"/>
</mappers>

//4自动扫描包下所有映射器
<mappers>
   <package name="org.mybatis.builder"/>
</mappers>

继续源码分析，我们在上面mybatis-config.xml解析中可以看到：

我们不妨进入这个方法看看：

private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
        for (XNode child : parent.getChildren()) {
            //自动扫描包下所有映射器
            if ("package".equals(child.getName())) {
                String mapperPackage = child.getStringAttribute("name");
                //放  
                configuration.addMappers(mapperPackage);
            } else {
                String resource = child.getStringAttribute("resource");
                String url = child.getStringAttribute("url");
                String mapperClass = child.getStringAttribute("class");
                //使用java类名
                if (resource != null && url == null && mapperClass == null) {
                    ErrorContext.instance().resource(resource);
                    //根据文件存放目录，读取XxxMapper.xml
                    InputStream inputStream = Resources.getResourceAsStream(resource);
                    //映射器比较复杂，调用XMLMapperBuilder
                    //注意在for循环里每个mapper都重新new一个XMLMapperBuilder，来解析
                    XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
                    mapperParser.parse();
                    //使用绝对url路径
                } else if (resource == null && url != null && mapperClass == null) {
                    ErrorContext.instance().resource(url);
                    InputStream inputStream = Resources.getUrlAsStream(url);
                    //映射器比较复杂，调用XMLMapperBuilder
                    XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
                    mapperParser.parse();
                    //使用类路径    
                } else if (resource == null && url == null && mapperClass != null) {
                    Class<?> mapperInterface = Resources.classForName(mapperClass);
                    //直接把这个映射加入配置
                    configuration.addMapper(mapperInterface);
                } else {
                    throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
                }
            }
        }
    }
}

这里刚刚和我们的上面说的<mapper>使用的方式完全是一模一样的。

到这里，配置文件mybatis-config.xml和我们定义映射文件XxxMapper.xml就全部解析完成。

回到SqlSessionFactoryBuilder类

前面讲到了XMLConfigBuilder中的parse方法，并返回了一个Configuration对象。

build(parser.parse());

这个build方法就是传入一个Configuration对象，然后构建一个DefaultSqlSession对象。

public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
}

继续回到我们的demo代码中这一行代码里：

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

这一行代码就相当于：

SqlSessionFactory sqlSessionFactory = new new DefaultSqlSessionFactory();

到这里，我们的整个流程就搞定了。

转载于：Mybatis是如何解析配置文件的？看完终于明白了