本次，将简单介绍一下Mybatis的配置文件：
上次例子中，我们以 SqlSessionFactoryBuilder 去创建 SqlSessionFactory, 那么，我们就先从SqlSessionFactoryBuilder入手， 咱们先看看源码是怎么实现的：
SqlSessionFactoryBuilder源码片段：
public class SqlSessionFactoryBuilder {
2
3 //Reader读取mybatis配置文件，传入构造方法
4 //除了Reader外，其实还有对应的inputStream作为参数的构造方法，
5 //这也体现了mybatis配置的灵活性
6 public SqlSessionFactory build(Reader reader) {
7 return build(reader, null, null);
8 }
9
10 public SqlSessionFactory build(Reader reader, String environment) {
11 return build(reader, environment, null);
12 }
13
14 //mybatis配置文件 + properties, 此时mybatis配置文件中可以不配置properties，也能使用${}形式
15 public SqlSessionFactory build(Reader reader, Properties properties) {
16 return build(reader, null, properties);
17 }
18
19 //通过XMLConfigBuilder解析mybatis配置，然后创建SqlSessionFactory对象
20 public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
21 try {
22 XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
23 //下面看看这个方法的源码
24 return build(parser.parse());
25 } catch (Exception e) {
26 throw ExceptionFactory.wrapException("Error building SqlSession.", e);
27 } finally {
28 ErrorContext.instance().reset();
29 try {
30 reader.close();
31 } catch (IOException e) {
32 // Intentionally ignore. Prefer previous error.
33 }
34 }
35 }
36
37 public SqlSessionFactory build(Configuration config) {
38 return new DefaultSqlSessionFactory(config);
39 }
40
41 }通过源码，我们可以看到SqlSessionFactoryBuilder 通过XMLConfigBuilder 去解析我们传入的mybatis的配置文件， 下面就接着看看 XMLConfigBuilder 部分源码下载地址 ：
/**
2 * mybatis 配置文件解析
3 */
4 public class XMLConfigBuilder extends BaseBuilder {
5 public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
6 this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
7 }
8
9 private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
10 super(new Configuration());
11 ErrorContext.instance().resource("SQL Mapper Configuration");
12 this.configuration.setVariables(props);
13 this.parsed = false;
14 this.environment = environment;
15 this.parser = parser;
16 }
17
18 //外部调用此方法对mybatis配置文件进行解析
19 public Configuration parse() {
20 if (parsed) {
21 throw new BuilderException("Each XMLConfigBuilder can only be used once.");
22 }
23 parsed = true;
24 //从根节点configuration
25 parseConfiguration(parser.evalNode("/configuration"));
26 return configuration;
27 }
28
29 //此方法就是解析configuration节点下的子节点
30 //由此也可看出，我们在configuration下面能配置的节点为以下10个节点
31 private void parseConfiguration(XNode root) {
32 try {
33 propertiesElement(root.evalNode("properties")); //issue #117 read properties first
34 typeAliasesElement(root.evalNode("typeAliases"));
35 pluginElement(root.evalNode("plugins"));
36 objectFactoryElement(root.evalNode("objectFactory"));
37 objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
38 settingsElement(root.evalNode("settings"));
39 environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631
40 databaseIdProviderElement(root.evalNode("databaseIdProvider"));
41 typeHandlerElement(root.evalNode("typeHandlers"));
42 mapperElement(root.evalNode("mappers"));
43 } catch (Exception e) {
44 throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
45 }
46 }
47 }
通过以上源码，我们就能看出，在mybatis的配置文件中：
1. configuration节点为根节点。
2. 在configuration节点之下，我们可以配置10个子节点， 分别为：properties、typeAliases、plugins、objectFactory、objectWrapperFactory、settings、environments、databaseIdProvider、typeHandlers、mappers
深入浅出Mybatis系列（二）---配置简介（mybatis源码篇）
原文：http://11551334.blog.51cto.com/11541334/1769990