Mybatis源码分析之SqlSessionFactoryBuilder

朴灿烈づ我的快乐病毒、 2022-01-22 09:59 307阅读 0赞

#### 1.首先是通过Resource中的getResourceAsReader方法加载配置文件信息。 ####

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
        
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                
                <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>
        
        <mappers>
            <mapper resource="mapper/UserMapper.xml"/>
        </mappers>
    
    </configuration>

// 1.定义mybatis_config文件地址
     String resources = "mybatis_config.xml";
     // 2.获取InputStreamReaderIo流
     Reader reader = Resources.getResourceAsReader(resources);

将读取的信息赋值对应的Reader对象。Resource中的getResourceAsReader方法底层使用IO流方式兑取配置文件。进入getResourceAsReader方法中：

public static Reader getResourceAsReader(String resource) throws IOException { 
        Reader reader;
        if (charset == null) { //charset:编码格式
          reader = new InputStreamReader(getResourceAsStream(resource));
        } else { 
          reader = new InputStreamReader(getResourceAsStream(resource), charset);
        }
        return reader;
      }

#### 2.通过SqlSessionFactoryBuilder获取SqlSessionFactory对象。 ####

// 3.获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);

2.1 进入SqlSessionFactoryBuilder中的builder方法，将reader通过XmlConfigBuilder对象将其解析，封装成Configuration对象。

//SqlSessionFactoryBuilder.class
    public SqlSessionFactory build(Reader reader) { 
        return build(reader, null, null);//进入
      }

//SqlSessionFactoryBuilder.class
    public SqlSessionFactory build(Reader reader, String environment, Properties properties) { 
        try { 
           //2.2.进入解析XMLConfigBuilder的有参构造
          XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
          return build(parser.parse());//2.3 进入parse方法 3.进入build方法中
        } catch (Exception e) { 
          throw ExceptionFactory.wrapException("Error building SqlSession.", e);
        } finally { 
          ErrorContext.instance().reset();
          try { 
            reader.close();
          } catch (IOException e) { 
            // Intentionally ignore. Prefer previous error.
          }
        }
      }

2.2 进入XMLConfigBuilder的有参构造方法：

private XMLConfigBuilder(XPathParser parser, String environment, Properties props) { 
        super(new Configuration());
        ErrorContext.instance().resource("SQL Mapper Configuration");
        this.configuration.setVariables(props);
        this.parsed = false;//设置parsed为false，目的为了只让Xml文件只加载一次
        this.environment = environment;
        this.parser = parser;
      }

2.3 进入parser.parse()方法：

public Configuration parse() { 
        if (parsed) {  //有参构造中设置为false，目的只为加载xml文件一次
          throw new BuilderException("Each XMLConfigBuilder can only be used once.");
        }
        parsed = true;
        parseConfiguration(parser.evalNode("/configuration"));
        return configuration;
      }

2.4 进入parseConfiguration方法中：

//解析xml文件节点信息，将信息封装到Configuration对象中
    private void parseConfiguration(XNode root) { 
        try { 
          //issue #117 read properties first
          propertiesElement(root.evalNode("properties"));
          typeAliasesElement(root.evalNode("typeAliases"));
          pluginElement(root.evalNode("plugins"));
          objectFactoryElement(root.evalNode("objectFactory"));
          objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
          reflectionFactoryElement(root.evalNode("reflectionFactory"));
          settingsElement(root.evalNode("settings"));
          // read it after objectFactory and objectWrapperFactory issue #631
          environmentsElement(root.evalNode("environments"));
          databaseIdProviderElement(root.evalNode("databaseIdProvider"));
          typeHandlerElement(root.evalNode("typeHandlers"));
          mapperElement(root.evalNode("mappers"));
        } catch (Exception e) { 
          throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
        }
      }

#### 3.然后使用configuration获取DefaultSqlSessionFactory对象，将其返回给SqlSessionFactory对象。 ####

1.  1进入build(parser.parse())方法中：

//SqlSessionFactoryBuilder.class
    public SqlSessionFactory build(Configuration config) { 
        return new DefaultSqlSessionFactory(config);
      }

#### 4.通过sqlSessionFactory就可以获取到session ####

// 4.获取Session
    SqlSession sqlSession = sqlSessionFactory.openSession();

#### 5.通过session去操作mapper ####

// 5.操作Mapper接口 使用代理模式
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);

#### 6.Mybatis执行流程图 ####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70_pic_center]

> 1.定义mbatis配置文件
> 
> 2.通过iO操作去读取到配置文件信息
> 
> 3.通过SqlSessionFactoryBuilder的 builder方法去（XmlConfigBuilder）解析xml配置文件，将配置信息装配到 Configuration对象中，返回SqlSessionFactory（XmlMapperBuilder解析mapperXml映射文件）
> 
> 4.通过SqlSessionFactory获取到session
> 
> 5.通过session使用代理模式去操作Mapper
> 
> 6.通过Mapper调用接口及执行sql并返回结果

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