mybatis通过接口查找对应的mapper.xml以及方法执行

在使用mybatis的时候，有一种方式是

BookMapper bookMapper = SqlSession().getMapper(BookMapper.class)

获取接口，然后调用接口的方法。只要方法名和对应的mapper.xml中的id名字相同，就可以执行sql。
那么接口是如何与mapper.xml对应的呢？
首先看下，在getMapper()方法是如何操作的。
在DefaultSqlSession.java中调用了configuration.getMapper()

public  T getMapper(Class type) {
    return configuration.getMapper(type, this);
  }

在Configuration.java中调用了mapperRegistry.getMapper(type, sqlSession)；

public  T getMapper(Class type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
  }

下面重点来了，在MapperRegistry.java中实现了动态代理

public  T getMapper(Class<T> type, SqlSession sqlSession) {
    final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
    if (mapperProxyFactory == null)
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

这个函数分两部分来看，首先是从map集合中获取接口代理，map集合的来源，第二部分获取代理后实例化，获取接口的方法，执行sql。
对于第一部分：集合的来源。
这个MapperRegistry.java中有个方法是addMappers();共有两个重载。

public void addMappers(String packageName, Class superType) {
    ResolverUtil> resolverUtil = new ResolverUtil>();
    //通过包名，查找该包下所有的接口进行遍历，放入集合中
    resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
    Set>> mapperSet = resolverUtil.getClasses();
    for (Class mapperClass : mapperSet) {
      addMapper(mapperClass);
    }
  }

 //解析包名下的接口
  public void addMappers(String packageName) {
    addMappers(packageName, Object.class);
  }

往上追溯该方法的调用是在SqlSessionFactory.build();时对配置文件的解析，其中对节点mappers的解析，这里先不赘述，

mapperElement(root.evalNode("mappers"));

private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
      //使用package节点进行解析配置
        if ("package".equals(child.getName())) {
          String mapperPackage = child.getStringAttribute("name");
          //注册包下的接口
          configuration.addMappers(mapperPackage);
        } else {
        //使用mapper节点
          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);
            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);
            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.");
          }
        }
      }
    }
  }

这是调用addMapper()的顺序。
同时在改方法中还有一个方法很重要

 public  void addMapper(Class type) {
    if (type.isInterface()) {
      if (hasMapper(type)) {
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        knownMappers.put(type, new MapperProxyFactory<T>(type));
        //根据接口名寻找同包下同名的xml或者mapper的namespace是该接口的xml
        //找到对用的xml后进行解析mapper节点里面的节点
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

这是通过接口的全路径来查找对应的xml。这里有两种方式解析，也就是我们平常xml文件放置位置的两种写法。
第一种是不加namespace，把xml文件放在和接口相同的路径下，同时xml的名字与接口名字相同，如接口名为Student.java，xml文件为Student.xml。在相同的包下。这种当时可以不加namespace.
第二种是加namespace,通过namespace来查找对应的xml.
到这就是接口名和xml的全部注册流程。
下面再说下第二部分就是通过动态代理获取接口名字来对应xml中的id。
主要有两个类MapperProxyFactory.java和MapperProxy.java
对于MapperProxyFactory.java

public class MapperProxyFactory {

  private final Class mapperInterface;
  private Map methodCache = new ConcurrentHashMap();
    //构造函数，获取接口类
  public MapperProxyFactory(Class mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  public Class getMapperInterface() {
    return mapperInterface;
  }

  public Map getMethodCache() {
    return methodCache;
  }

  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }
//供外部调用
  public T newInstance(SqlSession sqlSession) {
    final MapperProxy mapperProxy = new MapperProxy(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

}

在MapperProxy.java中进行方法的执行

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) {
      try {
        return method.invoke(this, args);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    //方法的执行
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }

至此，就是mybatis所有接口和xml的加载，以及通过动态代理来进行接口的执行的过程。