mappers標籤四種配置方式
上一篇中提到XMLConfigBuilder.mapperElement()方法,該方法用於對核心配置文件中<mappers>標籤的解析,先回顧一下<mappers>標籤中,對於mapper接口或映射文件的幾種引入方式:
<!-- 方式1:使用包名引入,通過name屬性指定mapper接口所在的包名,要求映射配置文件必須和接口同包同名 -->
<mappers>
<package name="com.mybatisTest.mapper"/>
</mappers>
<!-- 方式2:使用接口類引入,通過class屬性指定mapper接口,要求映射配置文件必須和接口同包同名 -->
<mappers>
<mapper class="com.mybatisTest.mapper.accountMapper"/>
</mappers>
<!-- 方式3:使用本地文件路徑引入,通過url指定映射配置文件的本地文件路徑-->
<mappers>
<mapper url="file:///var/mappers/accountMapper.xml"/>
</mappers>
<!-- 方式4:使用類路徑引入,通過resource屬性指定映射配置文件在classpath下的路徑-->
<mappers>
<mapper resource="com.mybatisTest.mapper.accountMapper.xml"/>
</mappers>
源碼分析
回到mapperElement()方法,可以看出對映射文件不同引入方式的解析
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
//使用包名引入
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");
//使用類路徑引入
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();
//使用本地文件路徑引入
} 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();
//使用接口類引入
} 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.");
}
}
}
}
}
如果使用類路徑或本地文件路徑引入,mybatis會先註冊接口,然後並且解析xml,掃描接口中的註解,時序圖如下:
使用類路徑或本地文件路徑引入,會先調用XMLMapperBuilder.parse()方法:
public void parse() {
//判斷是否已經加載過該映射配置文件
if (!configuration.isResourceLoaded(resource)) {
//從根節點<mapper>開始解析
configurationElement(parser.evalNode("/mapper"));
//將映射配置文件添加到loadedResources集合中,該集合記錄了已經加載的映射配置文件
configuration.addLoadedResource(resource);
//註冊Mapper接口
bindMapperForNamespace();
}
// 處理configurationElement()方法中解析失敗的<resultMap>節點
parsePendingResultMaps();
// 處理configurationElement()方法中解析失敗的<cache-ref>節點
parsePendingCacheRefs();
// 處理configurationElement()方法中解析失敗的SQL語句節點
parsePendingStatements();
}
而在bindMapperForNamespace()會調用configuration.addMapper(),完成mapper接口的註冊,以及接口中註解的解析:
private void bindMapperForNamespace() {
//獲取映射配置文件的命名空間
String namespace = builderAssistant.getCurrentNamespace();
if (namespace != null) {
Class<?> boundType = null;
try {
//通過反射得到namespace對應的Class對象
boundType = Resources.classForName(namespace);
} catch (ClassNotFoundException e) {
//ignore, bound type is not required
}
if (boundType != null) {
if (!configuration.hasMapper(boundType)) { //是否已經註冊boundType接口
// Spring may not know the real resource name so we set a flag
// to prevent loading again this resource from the mapper interface
// look at MapperAnnotationBuilder#loadXmlResource
configuration.addLoadedResource("namespace:" + namespace); //記錄namespace
configuration.addMapper(boundType); //調用MapperRegistry.addMapper()方法,註冊boundType接口
}
}
}
}
如果使用包名或接口類引入,mybatis會先解析xml,然後再去註冊接口,掃描接口中的註解,時序圖如下:
先調用configuration.addMapper()方法
public <T> void addMapper(Class<T> type) {
if (type.isInterface()) {
if (hasMapper(type)) { //已經註冊,拋出異常
throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
}
boolean loadCompleted = false;
try {
knownMappers.put(type, new MapperProxyFactory<>(type)); //完成註冊
// 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(); //解析接口文件中的註解,以及對應的映射配置文件
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
然後,會調用MapperAnnotationBuilder.parse()方法,該方法內部會進行映射配置文件的解析,以及註解的解析:
public void parse() {
String resource = type.toString();
if (!configuration.isResourceLoaded(resource)) {
//加載與這個接口相關聯的xml文件
loadXmlResource();
configuration.addLoadedResource(resource);
assistant.setCurrentNamespace(type.getName());
parseCache();
parseCacheRef();
Method[] methods = type.getMethods();
for (Method method : methods) {
try {
// issue #237
if (!method.isBridge()) {
parseStatement(method); //解析註解形式的statement
}
} catch (IncompleteElementException e) {
configuration.addIncompleteMethod(new MethodResolver(this, method));
}
}
}
parsePendingMethods();
}
在loadXmlResource()方法中,又會調用XMLMapperBuilder.parse()方法進行映射配置文件的解析
從這個方法可以看出,映射配置文件是通過 type.getName(),也就是接口的全類名找到的,這也就是爲什麼使用包名或接口類引入mapper接口,要求映射配置文件必須與接口同包同名了
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
//XMLMapperBuilder.bindMapperForNamespace()方法中的
// 使用configuration.addLoadedResource("namespace:" + namespace)標記namespace之後
//就不會再進行xml解析了
if (!configuration.isResourceLoaded("namespace:" + type.getName())) {
String xmlResource = type.getName().replace('.', '/') + ".xml";
// #1347
InputStream inputStream = type.getResourceAsStream("/" + xmlResource);
if (inputStream == null) {
// Search XML mapper that is not in the module but in the classpath.
try {
inputStream = Resources.getResourceAsStream(type.getClassLoader(), xmlResource);
} catch (IOException e2) {
// ignore, resource is not required
}
}
if (inputStream != null) {
XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());
xmlParser.parse();
}
}
}
總結:在使用mappers標籤,用包名和接口類引入mapper接口時,調用的順序是configuration.addMapper()->XMLMapperBuilder.parse(),而使用本地文件路徑和類路徑引入映射配置文件時,調用的順序是XMLMapperBuilder.parse()->configuration.addMapper(),當然爲了避免不斷地循環調用下去,會利用configuration.addLoadedResource()和configuration.isResourceLoaded()去設置和判斷flag。