MybatisSqlSessionFactoryBuilder源码的示例 分析，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。
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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();
}
}// 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：
// 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：
<configuration>
<!-- 环境配置 -->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<!-- 数据库连接相关配置 ,这里动态获取config.properties文件中的内容-->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/test"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<!-- mapping文件路径配置 -->
<mappers>
<mapper resource="mappers/UserMapper.xml"/>
</mappers>
</configuration>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：
我们看下这段代码：
this.configuration.setEnvironment(environmentBuilder.build());public void setEnvironment(Environment environment) {
this.environment = environment;
}
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：
<mapper namespace="com.mayikt.mapper.UserMapper">
<!-- 在select标签中编写查询的SQL语句， 设置select标签的id属性为getUser，id属性值必须是唯一的，不能够重复
使用parameterType属性指明查询时使用的参数类型，resultType属性指明查询返回的结果集类型
resultType="com.mayikt.entity.User"就表示将查询结果封装成一个User类的对象返回
User类就是users表所对应的实体类
-->
<!--
根据id查询得到一个user对象
-->
<select id="getUser" parameterType="int"
resultType="com.mayikt.entity.UserEntity">
select * from user where id=#{id}
</select>
</mapper>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：
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<String> 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：
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 <T> void addMapper(Class<T> type) {
this.mapperRegistry.addMapper(type);
}public <T> void addMapper(Class<T> 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：
最后，我们来看看loadedResources里面的东西：存放的是userMapper的配置文件
再看看mapperRegistery里面的东西：存放的是mapper接口
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
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;
}
}到这里，我们就结束了源码分析，下面总结下大体流程：
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
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