Mybatis深入源码分析之SqlSessionFactoryBuilder源码分析

一：源码分析代码片段

public static void main(String[] args) {

try {
    // 基本mybatis环境
    // 1.定义mybatis\_config文件地址
    String resources = "mybatis\_config.xml";
    // 2.获取InputStreamReaderIo流
    Reader reader = Resources.getResourceAsReader(resources);
    // 3.获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
    // 4.获取Session
    SqlSession sqlSession = sqlSessionFactory.openSession();
    // 5.操作Mapper接口
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    UserEntity user = mapper.getUser(2);
    System.out.println(user.getName());
} catch (Exception e) {
    e.printStackTrace();
}

}

首先对步骤2进行分析

// 2.获取InputStreamReaderIo流

Reader reader = Resources.getResourceAsReader(resources);

public static Reader getResourceAsReader(String resource) throws IOException { InputStreamReader reader; if (charset == null) { reader = new InputStreamReader(getResourceAsStream(resource)); } else { reader = new InputStreamReader(getResourceAsStream(resource), charset); }

return reader;

}

通过上述代码可知：使用了门面模式：定义了Resource类，把复杂过程封装起来，方便用户使用，返回reader为InputStreamReader，指的是读取的mybatis_config.xml文件，断点调试结果如下：

Mybatis深入源码分析之SqlSessionFactoryBuilder源码分析

第三步源码分析

// 3.获取SqlSessionFactory

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);

进入SqlSessionFactoryBuilder（）构造函数如下：

public SqlSessionFactoryBuilder() { }

可知，无参构造函数没用做任何事情，再进入build(reader)源码，reader参数为InputStream流

public SqlSessionFactory build(Reader reader) { return this.build((Reader)reader, (String)null, (Properties)null); }

public SqlSessionFactory build(Reader reader, String environment, Properties properties) { SqlSessionFactory var5; try { XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties); 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;

}

我们来分析下XMLConfigBuilder这个类是干嘛的，进入XMLConfigBuilder构造函数如下：

public XMLConfigBuilder(Reader reader, String environment, Properties props) { this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props); }

private XMLConfigBuilder(XPathParser parser, String environment, Properties props) { super(new Configuration()); this.localReflectorFactory = new DefaultReflectorFactory(); ErrorContext.instance().resource("SQL Mapper Configuration"); this.configuration.setVariables(props); this.parsed = false; this.environment = environment; this.parser = parser; }

进入super()代码如下：

public BaseBuilder(Configuration configuration) { this.configuration = configuration; this.typeAliasRegistry = this.configuration.getTypeAliasRegistry(); this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry(); }

通过上述代码可知：this.parsed = false;后面有用，这里先提下。返回原先执行处：var5 = this.build(parser.parse());

var5 = this.build(parser.parse());

进入parser.parse()这个方法，代码如下：

public Configuration parse() { if (this.parsed) { throw new BuilderException("Each XMLConfigBuilder can only be used once."); } else { this.parsed = true; this.parseConfiguration(this.parser.evalNode("/configuration")); return this.configuration; } }

由前面设置了this.parsed = false，可知this.parsed为false，就进入else分支，读者这个时候就有疑问了，为啥要设置this.parsed = false呢？

我们通过else分支可知，又设置了 this.parsed = true;说明再下一次再次进入parse方法的时候，this.parsed=true会直接抛出异常。

这里我们可以总结下：

为什么XMLConfigBuilder只能被使用一次呢？
答：因为我们的Configuration是一个全局的，所以只能被解析一次。
多次解析的话，会抛出：Each XMLConfigBuilder can only be used once.异常，防止用户私自调用parse（）方法再去重复解析，因为配置文件是全局的，不能多次解析。

进入else分支的下面这个代码中：

this.parseConfiguration(this.parser.evalNode("/configuration"));

private void parseConfiguration(XNode root) { try { this.propertiesElement(root.evalNode("properties")); this.typeAliasesElement(root.evalNode("typeAliases")); this.pluginElement(root.evalNode("plugins")); this.objectFactoryElement(root.evalNode("objectFactory")); this.objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); this.reflectionFactoryElement(root.evalNode("reflectionFactory")); this.settingsElement(root.evalNode("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); } }

我们先看看mybatis_config.xml配置文件的内容：

我们先进入下面这行代码：因为这个environments在我们配置文件中配置了，我们先分析它：

this.environmentsElement(root.evalNode("environments"))

private void environmentsElement(XNode context) throws Exception { if (context != null) { if (this.environment == null) { this.environment = context.getStringAttribute("default"); } Iterator i$ = context.getChildren().iterator(); while(i$.hasNext()) { XNode child = (XNode)i$.next(); String id = child.getStringAttribute("id"); if (this.isSpecifiedEnvironment(id)) { TransactionFactory txFactory = this.transactionManagerElement(child.evalNode("transactionManager")); DataSourceFactory dsFactory = this.dataSourceElement(child.evalNode("dataSource")); DataSource dataSource = dsFactory.getDataSource(); Builder environmentBuilder = (new Builder(id)).transactionFactory(txFactory).dataSource(dataSource); this.configuration.setEnvironment(environmentBuilder.build()); } } } }

通过断点调试environmentsElement（）代码结果如下：

Mybatis深入源码分析之SqlSessionFactoryBuilder源码分析

我们看下这段代码：

this.configuration.setEnvironment(environmentBuilder.build());

public void setEnvironment(Environment environment) { this.environment = environment; }

Mybatis深入源码分析之SqlSessionFactoryBuilder源码分析

到这里我们就明白了：这里将解析的XML结点封装成Environment对象，再把Environment对象设置给Configuration对象中。也就是解析XML,再把XML转为Configuration实体类

到这里我们再来分析：mappers结点在配置文件中配置了，我们也来分析下,下面是mapper.xml配置文件的内容，看下是如何转化为实体对象保存起来的：

this.mapperElement(root.evalNode("mappers"));

private void mapperElement(XNode parent) throws Exception { if (parent != null) { Iterator i$ = parent.getChildren().iterator(); while(true) { while(i$.hasNext()) { XNode child = (XNode)i$.next(); String resource; if ("package".equals(child.getName())) { //注解方式配置扫包package resource = child.getStringAttribute("name"); this.configuration.addMappers(resource); } else { //resource 方式 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; } } }

通过上述代码可知，配置方式有两种：一种是注解形式扫包，第二种是resource方式

我们是resource方式的配置，所以进入else分支：

Mybatis深入源码分析之SqlSessionFactoryBuilder源码分析

由上面断点分析可知，这里会读取mapper.xml配置文件的内容，转化为inputStream流，再解析mapper.xml配置文件

XMLMapperBuilder类的作用：解析mapper配置文件得到Configuration对象，我们看下XMLMapperBuilder怎么去解析mapper配置文件

public XMLMapperBuilder(InputStream inputStream, Configuration configuration, String resource, Map<String, XNode> sqlFragments) { this(new XPathParser(inputStream, true, configuration.getVariables(), new XMLMapperEntityResolver()), configuration, resource, sqlFragments); }

private XMLMapperBuilder(XPathParser parser, Configuration configuration, String resource, Map<String, XNode> sqlFragments) { super(configuration); this.builderAssistant = new MapperBuilderAssistant(configuration, resource); this.parser = parser; this.sqlFragments = sqlFragments; this.resource = resource; }

最终进入：

mapperParser.parse()

public void parse() { if (!this.configuration.isResourceLoaded(this.resource)) { this.configurationElement(this.parser.evalNode("/mapper")); this.configuration.addLoadedResource(this.resource); this.bindMapperForNamespace(); }

进入addLoadedResource（）方法：

public void addLoadedResource(String resource) { this.loadedResources.add(resource); }

protected final Set loadedResources;

public Configuration() { this.loadedResources = new HashSet(); }

通过上述代码可知：loadedResources存放的都是mybatis映射的文件路径地址【mapper.xml】，使用HashSet集合存放

存放进去之后，断点如下：

Mybatis深入源码分析之SqlSessionFactoryBuilder源码分析

我们进入下面这个方法：

this.bindMapperForNamespace();

private void bindMapperForNamespace() { String namespace = this.builderAssistant.getCurrentNamespace(); //拿到mapper.xml里面配置的namespace，这里是com.mayikt.mapper.UserMapper if (namespace != null) { Class boundType = null; try { boundType = Resources.classForName(namespace); //通过Java反射机制帮我去查找，这里得到interface com.mayikt.mapper.UserMapper } catch (ClassNotFoundException var4) { ; } if (boundType != null && !this.configuration.hasMapper(boundType)) {//判断mapper.xml配置文件是否注册过 this.configuration.addLoadedResource("namespace:" + namespace); this.configuration.addMapper(boundType); } } }

先看看addMapper方法：

this.configuration.addMapper(boundType);

public void addMapper(Class type) { this.mapperRegistry.addMapper(type); }

public void addMapper(Class type) { if (type.isInterface()) { //判断是否是接口类型 if (this.hasMapper(type)) { //再次判断是否注册过，如果注册过，则抛出异常 throw new BindingException("Type " + type + " is already known to the MapperRegistry."); } boolean loadCompleted = false; try { 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); } } }

this.knownMappers.put(type, new MapperProxyFactory(type));

private final Map<Class, MapperProxyFactory> knownMappers = new HashMap();

由上述代码可知：mapperRegistry作用是：存放dao层mapper接口，debug结果如下：

Mybatis深入源码分析之SqlSessionFactoryBuilder源码分析

最后，我们来看看loadedResources里面的东西：存放的是userMapper的配置文件

Mybatis深入源码分析之SqlSessionFactoryBuilder源码分析

再看看mapperRegistery里面的东西：存放的是mapper接口

Mybatis深入源码分析之SqlSessionFactoryBuilder源码分析

最后，我们回到开始的parse（）方法，上述代码执行完this.parseConfiguration(this.parser.evalNode("/configuration"))方法之后，返回configuration对象

到这里，我们就结束了源码分析，下面总结下大体流程：

总结:

获取本地InputStreamReader对象（mybatis配置文件）

调用SqlSessionFactoryBuilder

###再使用XMLConfigBuilder解析mybatis配置文件，装配到Configuration中。

将配置文件中的Mapper添加到Configuration mapperRegistry实现注册。

备注：mapperRegistry存放当前所有的mapper接口。

loadedResources里面的东西：存放的是userMapper的配置文件