我们的一个mybatis程序

        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();        //返回的DefaultSqlSessionFactory的实例
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder
                .build(ClassLoader.getSystemResourceAsStream("mybatis.xml"));
        SqlSession sqlSession = sqlSessionFactory.openSession();

SqlSessionFactory是Mybatis的一个核心类负责创建SqlSession

SqlSessionFactory是由SqlSessionFactoryBuilder的build方法创建

 public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
        SqlSessionFactory var5;
        try {
            XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
            var5 = this.build(parser.parse());
        } catch (Exception var14) {
            throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
        } finally {
            ErrorContext.instance().reset();

            try {
                inputStream.close();
            } catch (IOException var13) {
                ;
            }

        }

        return var5;
    }

内部调用了XMLConfigBuilder  parser 看名字 我们可以看出来他是负责解析mybatis.

    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;
        }
    }

this.parser.evalNode("/configuration")获得根节点 

 private void parseConfiguration(XNode root) {
        try {
            Properties settings = this.settingsAsPropertiess(root.evalNode("settings"));
            this.propertiesElement(root.evalNode("properties"));
            this.loadCustomVfs(settings);
            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(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);
        }
    }

settings|typeHandlers|mappers|properties逐个解析最终封装到Configuration  对象里面

  public SqlSessionFactory build(Configuration config) {
        return new DefaultSqlSessionFactory(config);
    }

最终将解析好的数据都封装到configuration里面 初始化DefaultSqlSessionFactory (建造者模式)

Configuration属性

TypeAliasRegistry

我们定义的别名

<typeAliases>
        <!-- 批量别名定义,指定包名，mybatis自动扫描包中的po类，自动定义别名，别名是类名(首字母大写或小写都可以,一般用小写) -->
        <package name="com.liqiang.entity" />
        <package name="com.liqiang.vo" />
    </typeAliases>

点开这个类的构造函数可以发现默认注册了很多基本类型的别名，这就是为什么我们int double不用指定全名称的原因

  public TypeAliasRegistry() {
        this.registerAlias("string", String.class);
        this.registerAlias("byte", Byte.class);
        this.registerAlias("long", Long.class);
        this.registerAlias("short", Short.class);
        this.registerAlias("int", Integer.class);
        this.registerAlias("integer", Integer.class);
        this.registerAlias("double", Double.class);
        this.registerAlias("float", Float.class);
        this.registerAlias("boolean", Boolean.class);        ......}

TypeHandlerRegistry

public TypeHandlerRegistry() {
        this.register((Class)Boolean.class, (TypeHandler)(new BooleanTypeHandler()));
        this.register((Class)Boolean.TYPE, (TypeHandler)(new BooleanTypeHandler()));
        this.register((JdbcType)JdbcType.BOOLEAN, (TypeHandler)(new BooleanTypeHandler()));
        this.register((JdbcType)JdbcType.BIT, (TypeHandler)(new BooleanTypeHandler()));        .....
}

注册我们自定义的TypeHandler，可以看到默认实现了很多，所以我们对于常见的类型不需要再定义typeHandle

mappedStatements

Map<String, MappedStatement> mappedStatements

mybatis会将所有select|update|insert|delete标签解析为MappedStatement对象的形式保存起来

内部主要属性：

ParameterMap  一对多ParametersMapping   保存参数的映射关系

ResultMap  一对多 ResultMapping 保存返回结果的映射关系

我们可以发现刚开始mybatis会将xml里面的每个标签通过configuration封装起来通过他初始化SqlSessionFactory

原文地址：https://www.cnblogs.com/LQBlog/p/9277786.html