Mybatis 源码解析三、Mapper接口与mapper.xml文件绑定

     一、流程图介绍整体过程

        

 

     

    1、首先根据MapperScannerConfigurer进行包扫描，扫描Mapper接口，生成Spring特定的描述，并将其交由MapperProxyFactory管理，后期会由其生成动态代理对象。

              ClassOathMapperScanner 中的doScan()方法。

                

1. GenericBeanDefinition definition = (GenericBeanDefinition) holder.getBeanDefinition();
3. if (logger.isDebugEnabled()) {
4. logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName()
5. + "' and '" + definition.getBeanClassName() + "' mapperInterface");
6. }
8. // the mapper interface is the original class of the bean
9. // but, the actual class of the bean is MapperFactoryBean
10. definition.getPropertyValues().add("mapperInterface", definition.getBeanClassName());
11. definition.setBeanClass(MapperFactoryBean.class);
13. definition.getPropertyValues().add("addToConfig", this.addToConfig);

    2、初始化SqlSessionFactoryBean。首先判定mybatis.xml中的mapper属性是否配置如果配置，解析Mapper接口添加到Configuration中。

            XMLConfigBuilder中的mapperElement()方法

            

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. }

    3、判定 SqlSessionFactoryBean节点中是否配置mapperLocations属性，也即mapper.xml文件所在位置。会根据mapper.xml文件中配置的命名空间，获取Mapper接口，并添加到Configuration中。

        XMLMapperBuilder中的bindMapperForNamespace()方法。

        

1. private void bindMapperForNamespace() {
2. String namespace = builderAssistant.getCurrentNamespace();
3. if (namespace != null) {
4. Class boundType = null;
5. try {
6. boundType = Resources.classForName(namespace);
7. } catch (ClassNotFoundException e) {
8. //ignore, bound type is not required
9. }
10. if (boundType != null) {
11. if (!configuration.hasMapper(boundType)) {
12. // Spring may not know the real resource name so we set a flag
13. // to prevent loading again this resource from the mapper interface
14. // look at MapperAnnotationBuilder#loadXmlResource
15. configuration.addLoadedResource("namespace:" + namespace);
16. configuration.addMapper(boundType);
17. }
18. }
19. }
20. }

    4、如果以上都没有配置，需要使用Mapper的代理对象时，就会使用包扫描获得的Mapper接口信息，解析Mapper接口，添加到Configuration中。

    5、Configuration添加Mapper接口过程。

        MapperRegistry总的addMapper()方法

        

1. public <T> void addMapper(Class<T> 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<T>(type));
9. // It's important that the type is added before the parser is run
10. // otherwise the binding may automatically be attempted by the
11. // 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. }

    5.1 根据接口信息获取mapper.xml文件，校验mapper.xml文件配置是否正确

        MapperAnnotationBuilder中的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. if (!method.isBridge()) { // issue #237
13. parseStatement(method);
14. }
15. } catch (IncompleteElementException e) {
16. configuration.addIncompleteMethod(new MethodResolver(this, method));
17. }
18. }
19. }
20. parsePendingMethods();
21. }

     MapperAnnotationBuilder中的loadXmlResource()方法

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 required
12. }
13. if (inputStream != null) {
14. XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());
15. xmlParser.parse();
16. }
17. }
18. }

        可以看到最后又回到了XMLMapperBuilder中的parse()方法。

    5.2 解析Mapper接口以及mapper.xml文件，将方法与sql文件进行绑定。

            

    5.3 使用JDK动态代理技术生成Mapper接口的代理对象，添加到Configuration中。