【mybatis源码解析】(三)MapperRegistry类解析

【mybatis源码解析】(一)mybatis执行流程以及实现原理
【mybatis源码解析】(二)详解mybatis中java动态代理模式的运用
【mybatis源码解析】(三)MapperRegistry类解析

系列文章目录前言一、MapperRegistry是什么？二、MapperRegistry初始化

前面两篇文章介绍了大体流程，这篇着重介绍跟MapperRegistry相关的类

MapperRegistry翻译过来就是映射器注册表
看看他的属性

config是存储了mybatis相关配置的类
knownMappers是一个以mpper接口类对象为key，MapperProxyFactory为值的map集合

构造函数需要传入配置对象

getMapper方法返回mapper的动态代理生成的对象

配置中是否拥有mapper

添加一个MapperFProxyFactory对象到map集合，初始化时候会调用

在Configuration类中我们可以看到MapperRegistry的属性创建，说明在创建Configuration类时候就创建了MapperRegistry对象。
Configuration类在XMLConfigBuilder类中完成了创建
接下来看看的XMLConfigBuilder的parseConfiguration(XNode root)方法

有一个mapperElement(root.evalNode(“mappers”));方法，进去看看

  private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {
          String mapperPackage = child.getStringAttribute("name");
          configuration.addMappers(mapperPackage);
        } else {
          String resource = child.getStringAttribute("resource");
          String url = child.getStringAttribute("url");
          String mapperClass = child.getStringAttribute("class");
          if (resource != null && url == null && mapperClass == null) {
            ErrorContext.instance().resource(resource);
            try(InputStream inputStream = Resources.getResourceAsStream(resource)) {
              XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
              mapperParser.parse();
            }
          } else if (resource == null && url != null && mapperClass == null) {
            ErrorContext.instance().resource(url);
            try(InputStream inputStream = Resources.getUrlAsStream(url)){
              XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
              mapperParser.parse();
            }
          } else if (resource == null && url == null && mapperClass != null) {
            Class mapperInterface = Resources.classForName(mapperClass);
            configuration.addMapper(mapperInterface);
          } else {
            throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
          }
        }
      }
    }
  }

处理方法总结来说就是解析xml配置，将mapper相关信息提出来，调用configuration.addMappers(mapperPackage)，将mapper加入MapperRegistry的knownMappers属性
就是这个方法

  public  void addMapper(Class type) {
    if (type.isInterface()) {
      if (hasMapper(type)) {//判重
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;//标志位
      try {
        knownMappers.put(type, new MapperProxyFactory<>(type));//创建MapperProxyFactory工厂类放入
        // It's important that the type is added before the parser is run
        // otherwise the binding may automatically be attempted by the
        // mapper parser. If the type is already known, it won't try.
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);//mapper其他配置解析生成
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }