1.配置解析入口方法
XMLConfigBuilder#parseConfiguration
mappers文件解析的过程，就是<mappers>标签的解析。
从代码中可以知道，mapperElement(root.evalNode("mappers"))方法做的mapper文件解析。
// XMLConfigBuilder
private void parseConfiguration(XNode root) {
try {
Properties settings = settingsAsPropertiess(root.evalNode("settings"));
//issue #117 read properties first
propertiesElement(root.evalNode("properties"));
loadCustomVfs(settings);
typeAliasesElement(root.evalNode("typeAliases"));
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// read it after objectFactory and objectWrapperFactory issue #631
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
2.mapper解析入口方法
XMLConfigBuilder#mapperElement
mapper解析过程我理解成一下几个步骤：
1.文件定位、载入
2.文件解析（本篇文章不做分析）
1) xml标签解析，例如<mapper><sql><select>等
2) 属性解析，例如resultMap,parameterType等
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
// 第1种定位方式：将包内的映射器接口实现全部注册为映射器
if ("package".equals(child.getName())) {
String mapperPackage = child.getStringAttribute("name");
configuration.addMappers(mapperPackage);
} else {
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
// 第3种定位方式：使用相对于类路径的资源引用
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) {
// 第4种定位方式：使用完全URL
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) {
// 第2种定位方式:使用映射器接口实现类的完全限定类名
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.");
}
}
}
}
}
2.1 mapper文件4种定位方式
1和2都是基于类定位的，3和4是基于xml文件地址定位的。
1.将包内的映射器接口实现全部注册为映射器
<mappers>
<package name="org.mybatis.builder"/>
</mappers>
2.使用映射器接口实现类的完全限定类名
<mappers>
<mapper class="org.mybatis.builder.AuthorMapper"/>
<mapper class="org.mybatis.builder.BlogMapper"/>
<mapper class="org.mybatis.builder.PostMapper"/>
</mappers>
3.使用相对于类路径的资源引用
<mappers>
<mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
<mapper resource="org/mybatis/builder/BlogMapper.xml"/>
<mapper resource="org/mybatis/builder/PostMapper.xml"/>
</mappers>
4.使用完全限定资源定位符（URL）
<mappers>
<mapper url="file:///var/mappers/AuthorMapper.xml"/>
<mapper url="file:///var/mappers/BlogMapper.xml"/>
<mapper url="file:///var/mappers/PostMapper.xml"/>
</mappers>
2.2 mapper文件定位
package和class这两种方式会多一步xml文件地址的定位；
1.接口注册
2.定位xml文件地址（根据接口找到xml文件）
3.解析xml
resource和url这两种方式直接就定位xml地址了。
1.解析xml（该方法会检测mapper接口是否注册了，没有就会重新注册）
2.注册接口（根据xml文件找到class接口）
mybatis通过VFS相关类来读取本地文件系统的。
由此可以看出，mapper文件的解析核心过程就两个：接口注册、解析xml，只不过顺序不一样。我们按照接口注册、解析xm的过程来分析。
2.3 接口注册
MapperProxyFactory包装了接口类，然后注册到knownMappers这个map集合中去。创建接口代理类的时候，会用到MapperProxyFactory，就是从这个集合中去寻找。
public void addMappers(String packageName); // configuration
/**
*mapperRegistry
*/
public void addMappers(String packageName);
public void addMappers(String packageName, Class<?> superType);
public <T> void addMapper(Class<T> type)
public void addMappers(String packageName, Class<?> superType) {
ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
Set<Class<? extends Class<?>>> mapperSet = resolverUtil.getClasses();
// 循环包下面的接口，然后添加
for (Class<?> mapperClass : mapperSet) {
addMapper(mapperClass);
}
}
// 添加mapper接口到knownMappers中，
private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();
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));
// It's important that the type is added before the parser is run
// otherwise the binding may automatically be attempted by the
// mapper parser. If the type is already known, it won't try.
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
2.4 mapper.xml文件加载和解析
XMLMapperBuilder 负责解析
/**
* MapperAnnotationBuilder
* package和class会走这个方法
*/
private void loadXmlResource() {
// Spring may not know the real resource name so we check a flag
// to prevent loading again a resource twice
// this flag is set at XMLMapperBuilder#bindMapperForNamespace
if (!configuration.isResourceLoaded("namespace:" + type.getName())) {
String xmlResource = type.getName().replace('.', '/') + ".xml";
InputStream inputStream = null;
try {
inputStream = Resources.getResourceAsStream(type.getClassLoader(), xmlResource);
} catch (IOException e) {
// ignore, resource is not required
}
if (inputStream != null) {
XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());
xmlParser.parse();
}
}
}
/**
* XMLMapperBuilder
* 最终都会执行该方法
*/
public void parse() {
if (!configuration.isResourceLoaded(resource)) {
configurationElement(parser.evalNode("/mapper"));
configuration.addLoadedResource(resource);
bindMapperForNamespace();
}
parsePendingResultMaps();
parsePendingChacheRefs();
parsePendingStatements();
}
总结：
1.基于接口的解析，调用的是configuration.addMapper(mapperInterface)，先注册接口，然后在解析xml。
2.基于文件定位的解析，调用的是XMLMapperBuilder.parse()，先解析xml，然后在注册接口。
本篇文章只是对mapper.xml文件解析过程做了分析，其中的具体元素标签解析属于细节分析，我会在写一篇文章分析。
