# 第07章 Configuration对象总结及其手动创建
# 7.1 创建Configuration对象的过程
第02章中结合源码分析，有较详细的描述MyBatis基本的初始化过程（省略掉部分细节）：
- 当SqlSessionFactoryBuilder执行build()方法，调用了XMLConfigBuilder的parse()方法，然后返回了Configuration对象。XMLConfigBuilder会将XML配置文件的信息转换为Document对象，而XML配置定义文件DTD转换成XMLMapperEntityResolver对象，然后将二者封装到XpathParser对象中，XpathParser的作用是提供根据Xpath表达式获取基本的DOM节点Node信息的操作。如下图所示：
- 之后XMLConfigBuilder调用parse()方法：会从XPathParser中取出
<configuration>节点对应的Node对象，然后解析此Node节点的子Node：properties, settings, typeAliases,typeHandlers, objectFactory, objectWrapperFactory, plugins, environments,databaseIdProvider, mappers
public Configuration parse() {
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
/**
* 解析 "/configuration"节点下的子节点信息，然后将解析的结果设置到Configuration对象中
*/
private void parseConfiguration(XNode root) {
try {
//1.首先处理properties 节点
propertiesElement(root.evalNode("properties"));
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
loadCustomLogImpl(settings);
//2.处理typeAliases
typeAliasesElement(root.evalNode("typeAliases"));
//3.处理插件
pluginElement(root.evalNode("plugins"));
//4.处理objectFactory
objectFactoryElement(root.evalNode("objectFactory"));
//5.objectWrapperFactory
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
reflectorFactoryElement(root.evalNode("reflectorFactory"));
//6.settings
settingsElement(settings);
//7.处理environments
environmentsElement(root.evalNode("environments"));
//8.databaseIdProvider
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
//9.typeHandlers
typeHandlerElement(root.evalNode("typeHandlers"));
//10.mappers
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
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- 然后将这些值解析出来设置到Configuration对象中
以environmentsElement(root.evalNode("environments")); 方法为例，讲解如何将environments的信息解析出来，设置到Configuration对象中的：
/*
解析environments节点，并将结果设置到Configuration对象中
注意：创建envronment时，如果SqlSessionFactoryBuilder指定了特定的环境（即数据源）；
则返回指定环境（数据源）的Environment对象，否则返回默认的Environment对象；
这种方式实现了MyBatis可以连接多数据源
*/
private void environmentsElement(XNode context) throws Exception{
if (context != null){
if (environment == null){
environment = context.getStringAttribute("default");
}
for (XNode child : context.getChildren()){
String id = child.getStringAttribute("id");
if (isSpecifiedEnvironment(id)){
//1.创建事务工厂 TransactionFactory
TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
//2.创建数据源DataSource
DataSource dataSource = dsFactory.getDataSource();
//3. 构造Environment对象
Environment.Builder environmentBuilder = new Environment.Builder(id)
.transactionFactory(txFactory)
.dataSource(dataSource);
//4. 将创建的Envronment对象设置到configuration 对象中
configuration.setEnvironment(environmentBuilder.build());
}
}
}
}
private boolean isSpecifiedEnvironment(String id){
if (environment == null){
throw new BuilderException("No environment specified.");
}
else if (id == null){
throw new BuilderException("Environment requires an id attribute.");
}
else if (environment.equals(id)){
return true;
}
return false;
}
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- 返回Configuration对象
序列图：
# 7.2 手动加载XML配置文件
可以手动加载XML配置文件创建Configuration对象完成初始化，创建并使用SqlSessionFactory对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
//手动创建XMLConfigBuilder，并解析创建Configuration对象
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, null,null);
Configuration configuration=parser.parse();
//使用Configuration对象创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
//使用MyBatis
SqlSession sqlSession = sqlSessionFactory.openSession();
List list = sqlSession.selectList("com.foo.bean.BlogMapper.queryAllBlogInfo");
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