1.首先进入sqlSessionFactoryBuilder.build()方法
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
SqlSessionFactory var5;
try {
// 核心配置Configuration的XML解析
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
var5 = this.build(parser.parse());
} catch (Exception var14) {
throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
} finally {
ErrorContext.instance().reset();
try {
inputStream.close();
} catch (IOException var13) {
}
}
2.进入XMLConfigBuilder的parse()方法，再进入parseConfiguration(XNode root)方法，这里利用构建者模式的依次解析核心XML中的各个标签构建Configuration对象
private void parseConfiguration(XNode root) {
try {
this.propertiesElement(root.evalNode("properties"));
Properties settings = this.settingsAsProperties(root.evalNode("settings"));
this.loadCustomVfs(settings);
this.typeAliasesElement(root.evalNode("typeAliases"));
this.pluginElement(root.evalNode("plugins"));
this.objectFactoryElement(root.evalNode("objectFactory"));
this.objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
this.reflectorFactoryElement(root.evalNode("reflectorFactory"));
this.settingsElement(settings);
this.environmentsElement(root.evalNode("environments"));
this.databaseIdProviderElement(root.evalNode("databaseIdProvider"));
this.typeHandlerElement(root.evalNode("typeHandlers"));
this.mapperElement(root.evalNode("mappers"));
} catch (Exception var3) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + var3, var3);
}
}
3.进入mappers解析方法并找到cache标签的解析方法进入即XMLMapperBuilder的cacheElement(XNode context)方法，这里获取cache标签的各个配置属性，并调用builderAssistant.useNewCache()进行构建。
private void cacheElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type", "PERPETUAL");
Class<? extends Cache> typeClass = this.typeAliasRegistry.resolveAlias(type);
String eviction = context.getStringAttribute("eviction", "LRU");
Class<? extends Cache> evictionClass = this.typeAliasRegistry.resolveAlias(eviction);
Long flushInterval = context.getLongAttribute("flushInterval");
Integer size = context.getIntAttribute("size");
boolean readWrite = !context.getBooleanAttribute("readOnly", false);
boolean blocking = context.getBooleanAttribute("blocking", false);
Properties props = context.getChildrenAsProperties();
this.builderAssistant.useNewCache(typeClass, evictionClass, flushInterval, size, readWrite, blocking, props);
}
4.进入useNewCache（）方法发现，创建一个Cache接口的实现类即二级缓存对象，并分别存入核心配置类Configuration对对象，和MapperBuilderAssistant对象中，由于MapperBuilderAssistant属于XMLMapperBuilder，即XMLMapperBuilder中存在一个二级缓存（又源码得知一个mapper标签一个XMLMapperBuilder对象）。
public Cache useNewCache(Class<? extends Cache> typeClass, Class<? extends Cache> evictionClass, Long flushInterval, Integer size, boolean readWrite, boolean blocking, Properties props) {
Cache cache = (new CacheBuilder(this.currentNamespace)).implementation((Class)this.valueOrDefault(typeClass, PerpetualCache.class)).addDecorator((Class)this.valueOrDefault(evictionClass, LruCache.class)).clearInterval(flushInterval).size(size).readWrite(readWrite).blocking(blocking).properties(props).build();
this.configuration.addCache(cache);
this.currentCache = cache;
return cache;
}
5.继续回到XMLConfigBuilder解析mapperXML的mapperElement(XNode parent)方法，然后进入解析mapperXML的具体方法即XMLMapperBuilder的parse()方法。
XMLConfigBuilder.class
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
Iterator var2 = parent.getChildren().iterator();
while(true) {
while(var2.hasNext()) {
XNode child = (XNode)var2.next();
String resource;
if ("package".equals(child.getName())) {
resource = child.getStringAttribute("name");
this.configuration.addMappers(resource);
} else {
resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
XMLMapperBuilder mapperParser;
InputStream inputStream;
if (resource != null && url == null && mapperClass == null) {
ErrorContext.instance().resource(resource);
inputStream = Resources.getResourceAsStream(resource);
mapperParser = new XMLMapperBuilder(inputStream, this.configuration, resource, this.configuration.getSqlFragments());
//解析mapperXML的具体方法
mapperParser.parse();
} else if (resource == null && url != null && mapperClass == null) {
ErrorContext.instance().resource(url);
inputStream = Resources.getUrlAsStream(url);
mapperParser = new XMLMapperBuilder(inputStream, this.configuration, url, this.configuration.getSqlFragments());
mapperParser.parse();
} else {
if (resource != null || url != null || mapperClass == null) {
throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
Class<?> mapperInterface = Resources.classForName(mapperClass);
this.configuration.addMapper(mapperInterface);
}
}
}
return;
}
}
}
XMLMapperBuilder.class
public void parse() {
if (!this.configuration.isResourceLoaded(this.resource)) {
this.configurationElement(this.parser.evalNode("/mapper"));
this.configuration.addLoadedResource(this.resource);
this.bindMapperForNamespace();
}
this.parsePendingResultMaps();
this.parsePendingCacheRefs();
this.parsePendingStatements();
}
6.找到解析select,insert,update,delete标签的方法，即组装MappedStatement的方法MapperBuilderAssistant的addMappedStatement（）方法
public MappedStatement addMappedStatement( String id, ...) {
if (unresolvedCacheRef) {
throw new IncompleteElementException("Cache-ref not yet resolved"); }id = applyCurrentNamespace(id, false); boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
//创建MappedStatement对象
MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType) .flushCacheRequired(valueOrDefault(flushCache, !isSelect)) .useCache(valueOrDefault(useCache, isSelect))
// 在这里将之前放到MapperBuilderAssistant中的二级缓存Cache封装到MappedStatement
.cache(currentCache);
总结：
同一个mapperXML中各个增删改查标签公用一个二级缓存，所以说二级缓存是Mapper级别的。
陶某*____*