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

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

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

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
 final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) 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);
 }
 }

public void addMappers(String packageName, Class<?> superType) {
 ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
 //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<Class<? extends Class<?>>> 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);
 }

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.");
   }
  }
  }
 }
 }

 public <T> void addMapper(Class<T> 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);
  }
  }
 }
 }

public class MapperProxyFactory<T> {

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

 public Class<T> getMapperInterface() {
 return mapperInterface;
 }

 public Map<Method, MapperMethod> getMethodCache() {
 return methodCache;
 }

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

}

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;
 }