概述
前面几篇文章主要看了mybatis配置文件configuation.xml中<setting>,<environments>标签的加载，接下来看一下mapper标签的解析，先来看下标签的配置：
12 3 4 5 6 7 8 9 10
常用的主要就有上面三种方式，指定mapper的xml文件，指定package，指定mapper文件，我们来具体解析下。
解析
我们看下具体开始解析的代码：
1 private void mapperElement(XNode parent) throws Exception { 2 if (parent != null) { 3 for (XNode child : parent.getChildren()) { 4 if ("package".equals(child.getName())) { 5 String mapperPackage = child.getStringAttribute("name"); 6 configuration.addMappers(mapperPackage); 7 } else { 8 String resource = child.getStringAttribute("resource"); 9 String url = child.getStringAttribute("url");10 String mapperClass = child.getStringAttribute("class");11 if (resource != null && url == null && mapperClass == null) {12 ErrorContext.instance().resource(resource);13 InputStream inputStream = Resources.getResourceAsStream(resource);14 XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());15 mapperParser.parse();16 } else if (resource == null && url != null && mapperClass == null) {17 ErrorContext.instance().resource(url);18 InputStream inputStream = Resources.getUrlAsStream(url);19 XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());20 mapperParser.parse();21 } else if (resource == null && url == null && mapperClass != null) {22 Class mapperInterface = Resources.classForName(mapperClass);23 configuration.addMapper(mapperInterface);24 } else {25 throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");26 }27 }28 }29 }30 } 这段代码就是针对上面不同的配置进行解析加载，这里面还有一种url的情况，是通过url加载外部的资源，不常用。
我们先来看配置了package的情形，
第5行代码，获取包名，第6行代码调用configuration的addMappers方法，具体看下：
1 public void addMappers(String packageName) {2 mapperRegistry.addMappers(packageName);3 } configuation中又调用了mapperRegistry的addMappers方法：
1 public void addMappers(String packageName) {2 addMappers(packageName, Object.class);3 } 在看下addMappers方法：
1 public void addMappers(String packageName, Class superType) {2 ResolverUtil > resolverUtil = new ResolverUtil >();3 resolverUtil.find(new ResolverUtil.IsA(superType), packageName);4 Set >> mapperSet = resolverUtil.getClasses();5 for (Class mapperClass : mapperSet) {6 addMapper(mapperClass);7 }8 } 上面这段代码主要就是利用ResolverUtil遍历package下面的所有class文件，看下find方法：
1 public ResolverUtilfind(Test test, String packageName) { 2 String path = getPackagePath(packageName); 3 4 try { 5 List children = VFS.getInstance().list(path); 6 for (String child : children) { 7 if (child.endsWith(".class")) { 8 addIfMatching(test, child); 9 }10 }11 } catch (IOException ioe) {12 log.error("Could not read package: " + packageName, ioe);13 }14 15 return this;16 }
很明显，上面就是根据包名获取下面的class，然后调用addIfMatching方法：
1 protected void addIfMatching(Test test, String fqn) { 2 try { 3 String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.'); 4 ClassLoader loader = getClassLoader(); 5 if (log.isDebugEnabled()) { 6 log.debug("Checking to see if class " + externalName + " matches criteria [" + test + "]"); 7 } 8 9 Class type = loader.loadClass(externalName);10 if (test.matches(type)) {11 matches.add((Class ) type);12 }13 } catch (Throwable t) {14 log.warn("Could not examine class '" + fqn + "'" + " due to a " +15 t.getClass().getName() + " with message: " + t.getMessage());16 }17 } 这个方法主要就是根据前面传过来的class，去加载这个类，注意这边用的类加载器是线程上下文类加载器，然后判断这个类的类型是不是Object类，是的话，就放入matches这个set中，都遍历完成之后，符合要求的class就在这个set中，怎么获取呢？看下getClass方法：
1 public Set> getClasses() {2 return matches;3 }
这边调用getClass方法时就返回了这个Set，我们接着看mapperRegistry的addMappers方法，
1 public void addMappers(String packageName, Class superType) {2 ResolverUtil > resolverUtil = new ResolverUtil >();3 resolverUtil.find(new ResolverUtil.IsA(superType), packageName);4 Set >> mapperSet = resolverUtil.getClasses();5 for (Class mapperClass : mapperSet) {6 addMapper(mapperClass);7 }8 } 按照上面的分析，第4行代码，我们已经得到的复合条件的class，下面就是遍历这些class，调用addMapper方法：
1 publicvoid addMapper(Class type) { 2 if (type.isInterface()) { 3 if (hasMapper(type)) { 4 throw new BindingException("Type " + type + " is already known to the MapperRegistry."); 5 } 6 boolean loadCompleted = false; 7 try { 8 knownMappers.put(type, new MapperProxyFactory (type)); 9 // It's important that the type is added before the parser is run10 // otherwise the binding may automatically be attempted by the11 // mapper parser. If the type is already known, it won't try.12 MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);13 parser.parse();14 loadCompleted = true;15 } finally {16 if (!loadCompleted) {17 knownMappers.remove(type);18 }19 }20 }21 }
这段代码首先判断这个class的类型是不是接口，不是则直接跳过，是的话，判断这个class对应的mapper文件是不是已经加载了，是的话，则抛出异常，否则看下第8行代码，将当前class类作为key，new一个MapperProxyFactory作为value放入knownMappers这个map中，这边这个MapperProxyFactory我们后面会详细介绍，看第12行代码，这边new了一个MapperAnnotationBuilder，看下第13行代码，调用了MapperAnnotationBuilder的parse方法：
1 public void parse() { 2 String resource = type.toString(); 3 if (!configuration.isResourceLoaded(resource)) { 4 loadXmlResource(); 5 configuration.addLoadedResource(resource); 6 assistant.setCurrentNamespace(type.getName()); 7 parseCache(); 8 parseCacheRef(); 9 Method[] methods = type.getMethods();10 for (Method method : methods) {11 try {12 // issue #23713 if (!method.isBridge()) {14 parseStatement(method);15 }16 } catch (IncompleteElementException e) {17 configuration.addIncompleteMethod(new MethodResolver(this, method));18 }19 }20 }21 parsePendingMethods();22 } 这边我们只要关注第4行代码，第5行代码之后都是针对注解做的处理，具体看下：
1 private void loadXmlResource() { 2 // Spring may not know the real resource name so we check a flag 3 // to prevent loading again a resource twice 4 // this flag is set at XMLMapperBuilder#bindMapperForNamespace 5 if (!configuration.isResourceLoaded("namespace:" + type.getName())) { 6 String xmlResource = type.getName().replace('.', '/') + ".xml"; 7 InputStream inputStream = null; 8 try { 9 inputStream = Resources.getResourceAsStream(type.getClassLoader(), xmlResource);10 } catch (IOException e) {11 // ignore, resource is not required12 }13 if (inputStream != null) {14 XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());15 xmlParser.parse();16 }17 }18 } 这边首先再次确认xml文件有没有被加载过，没有的话继续加载，在当前目录下根据mapper的名字寻找xml文件，然后加载成流，之后交给XmlMapperBuilder处理，其实到这边，xml就已经加载完成了，后续都是处理一些使用了注解的东西，使用注解我们暂且不看。
我们再来看下方法三：
mapperClass不为空，走第三个if：
1 private void mapperElement(XNode parent) throws Exception { 2 if (parent != null) { 3 for (XNode child : parent.getChildren()) { 4 if ("package".equals(child.getName())) { 5 String mapperPackage = child.getStringAttribute("name"); 6 configuration.addMappers(mapperPackage); 7 } else { 8 String resource = child.getStringAttribute("resource"); 9 String url = child.getStringAttribute("url");10 String mapperClass = child.getStringAttribute("class");11 if (resource != null && url == null && mapperClass == null) {12 ErrorContext.instance().resource(resource);13 InputStream inputStream = Resources.getResourceAsStream(resource);14 XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());15 mapperParser.parse();16 } else if (resource == null && url != null && mapperClass == null) {17 ErrorContext.instance().resource(url);18 InputStream inputStream = Resources.getUrlAsStream(url);19 XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());20 mapperParser.parse();21 } else if (resource == null && url == null && mapperClass != null) {22 Class mapperInterface = Resources.classForName(mapperClass);23 configuration.addMapper(mapperInterface);24 } else {25 throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");26 }27 }28 }29 }30 } 第22行代码，根据名称加载mapper类，然后调用configuation的addMapper方法，这个我们上面已经分析过了，其实这种情况跟用package的很相似，可以说是一种特殊情况，package里面会有很多的mapper。
我们再看下方法一：
resource不为空：
1 if (resource != null && url == null && mapperClass == null) {2 ErrorContext.instance().resource(resource);3 InputStream inputStream = Resources.getResourceAsStream(resource);4 XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());5 mapperParser.parse();6 }
这边跟上面那个部分一样的，我们下一篇文章就主要看下这个解析过程。