深入浅出Mybatis系列(二)---配置简介(mybatis源码篇)

上篇文章《深入浅出Mybatis系列(一)---Mybatis入门》, 写了一个Demo简单体现了一下Mybatis的流程。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:

深入浅出Mybatis系列(二)---配置简介(mybatis源码篇)
 1 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 }
深入浅出Mybatis系列(二)---配置简介(mybatis源码篇)

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:

深入浅出Mybatis系列(二)---配置简介(mybatis源码篇)
 1 /**
 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 }
深入浅出Mybatis系列(二)---配置简介(mybatis源码篇)

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。

上一篇:Spring的jar包详解


下一篇:5分钟用Spring4 搭建一个REST WebService(转)