BookMapper bookMapper = SqlSession().getMapper(BookMapper.class)
獲取接口，然後調用接口的方法。只要方法名和對應的mapper.xml中的id名字相同，就可以執行sql。
那麽接口是如何與mapper.xml對應的呢？
首先看下，在getMapper()方法是如何操作的。
在DefaultSqlSession.java中調用了configuration.getMapper()
public <T> T getMapper(Class<T> type) {
return configuration.<T>getMapper(type, this);
}
在Configuration.java中調用了mapperRegistry.getMapper(type, sqlSession)；
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
下面重點來了，在MapperRegistry.java中實現了動態代理
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);
}
}
這個函數分兩部分來看，首先是從map集合中獲取接口代理，map集合的來源，第二部分獲取代理後實例化，獲取接口的方法，執行sql。
對於第壹部分：集合的來源。
這個MapperRegistry.java中有個方法是addMappers();***有兩個重載。
public void addMappers(String packageName, Class<?> superType) {
ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
//通過包名，查找該包下所有的接口進行遍歷，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);
}
往上追溯該方法的調用是在SqlSessionFactory.build();時對配置文件的解析，其中對節點mappers的解析，這裏先不贅述，
mapperElement(root.evalNode("mappers"));
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
//使用package節點進行解析配置
if ("package".equals(child.getName())) {
String mapperPackage = child.getStringAttribute("name");
//註冊包下的接口
configuration.addMappers(mapperPackage);
} else {
//使用mapper節點
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.");
}
}
}
}
}
這是調用addMapper()的順序。
同時在改方法中還有壹個方法很重要
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));
//根據接口名尋找同包下同名的xml或者mapper的namespace是該接口的xml
//找到對用的xml後進行解析mapper節點裏面的節點
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
這是通過接口的全路徑來查找對應的xml。這裏有兩種方式解析，也就是我們平常xml文件放置位置的兩種寫法。
第壹種是不加namespace，把xml文件放在和接口相同的路徑下，同時xml的名字與接口名字相同，如接口名為Student.java，xml文件為Student.xml。在相同的包下。這種當時可以不加namespace.
第二種是加namespace,通過namespace來查找對應的xml.
到這就是接口名和xml的全部註冊流程。
下面再說下第二部分就是通過動態代理獲取接口名字來對應xml中的id。
主要有兩個類MapperProxyFactory.java和MapperProxy.java
對於MapperProxyFactory.java
public class MapperProxyFactory<T> {
private final Class<T> mapperInterface;
private Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>();
//構造函數，獲取接口類
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);
}
//供外部調用
public T newInstance(SqlSession sqlSession) {
final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
}
在MapperProxy.java中進行方法的執行
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);
//方法的執行
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的加載，以及通過動態代理來進行接口的執行的過程。