mybatis源码解析（一）
mybatis原理解析
测试类开始进行测试
@Test
public void test01() throws IOException {
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis-config.xml"));
SqlSession sqlSession = sqlSessionFactory.openSession();
DocMapper mapper = sqlSession.getMapper(DocMapper.class);
Doc doc = mapper.getDocById(2);
System.out.println(doc);
}
-
首先先创建SQLSessionFactoryBuilder()对象，调用build()方法构建sqlSessionFactory对象
这里调用build方法需要 resource（配置文件的路径地址），environment、properties 三个参数，后两个默认可以为空 -
这里我们查看源码
public SqlSessionFactory build(Reader reader, Properties properties) {
return this.build((Reader)reader, (String)null, properties);
}
public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
SqlSessionFactory var5;
try {
//解析配置文件
XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
//通过解析结果 构建SqlSessionFactory对象 ，这里默认是使用的 DefaultSqlSessionFactory来构建 sqlSessionFactory对象
var5 = this.build(parser.parse());
} catch (Exception var14) {
throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
} finally {
ErrorContext.instance().reset();
try {
reader.close();
} catch (IOException var13) {
}
}
return var5;
}
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
- 通过这两段源码我们可以知道XMLConfigBuilder对象会解析配置文件（mybatis-config.xml），然后将解析结果交由DefaultSqlSssionFactory对象来创建 SqlSessionFactory对象
下面我们来看一下XMLConfigBulider对象是如何解析mybatis-config.xml 配置文件的
//我们主要观看这个方法的内部实现
parser.parse()
//进入方法的内部
public Configuration parse() {
if (this.parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
} else {
this.parsed = true;
//找到主节点并进行解析
this.parseConfiguration(this.parser.evalNode("/configuration"));
return this.configuration;
}
}
//进入parseConfiguration()方法
private void parseConfiguration(XNode root) {
try {
this.propertiesElement(root.evalNode("properties"));
Properties settings = this.settingsAsProperties(root.evalNode("settings"));
this.loadCustomVfs(settings);
this.loadCustomLogImpl(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);
}
}
- 这里我们其实可以看出xmlConfigBuilder是在对配置文件中的每一个节点进行解析
我们重点看看mappers配置 的解析
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());
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;
}
}
}
- 这里我们可以看到有一个 mapperParser.parse()方法，我们查看一下源码
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();
}
- 因为mapperElement（）方法中会循环遍历每一个mapper，每一个mapper配置都会进入该方法中
这里我们重点看一下bindMapperForNamespace()方法查找绑定指定命名空间
private void bindMapperForNamespace() {
String namespace = this.builderAssistant.getCurrentNamespace();
if (namespace != null) {
Class boundType = null;
try {
boundType = Resources.classForName(namespace);
} catch (ClassNotFoundException var4) {
}
if (boundType != null && !this.configuration.hasMapper(boundType)) {
this.configuration.addLoadedResource("namespace:" + namespace);
this.configuration.addMapper(boundType);
}
}
}
- 这里我们Resources.classForName(namespace) 是通过命名空间将指定的接口通过类加载器进行注册返回一个字节码对象
public static Class classForName(String className) throws ClassNotFoundException {
return classLoaderWrapper.classForName(className);
}
public Class classForName(String name) throws ClassNotFoundException {
return this.classForName(name, this.getClassLoaders((ClassLoader)null));
}
Class classForName(String name, ClassLoader[] classLoader) throws ClassNotFoundException {
ClassLoader[] var3 = classLoader;
int var4 = classLoader.length;
for(int var5 = 0; var5 < var4; ++var5) {
ClassLoader cl = var3[var5];
if (null != cl) {
try {
//重点看这里，通过类名创建字节码对象
Class c = Class.forName(name, true, cl);
if (null != c) {
return c;
}
} catch (ClassNotFoundException var8) {
}
}
}
- this.configuration.addMapper(boundType) 将命名空间的字节码对象注册到mapper中
public void addMapper(Class type) {
this.mapperRegistry.addMapper(type);
}
public void addMapper(Class type) {
if (type.isInterface()) {
if (this.hasMapper(type)) {
throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
}
boolean loadCompleted = false;
try {
//将type也就是我们的命名空间对象mapper放在一个map集合中作为一个key
this.knownMappers.put(type, new MapperProxyFactory(type));
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(this.config, type);
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
this.knownMappers.remove(type);
}
}
}
}
private final Map, MapperProxyFactory> knownMappers = new HashMap();
- 这里我们可以看出是将命名空间所对应的字节码对象注册到了knownMappers 对象中
- 后面我们可以翻看sqlSessionFactory.onpeSession() .getMapper()方法其实就是从knownMapper对象中取出一个注册好的mapper
第一部分我们先说到这里