我是大叔

问答

采用 Configuration 注册 Mapper，他是怎么去加载对应的 mapper.xml 的？
// MapperAnnotationBuilder
private void loadXmlResource() {
  // Spring may not know the real resource name so we check a flag
  // to prevent loading again a resource twice
  // this flag is set at XMLMapperBuilder#bindMapperForNamespace
  // xml 的id "namespace:xxx.xx.xx.UserMapper"
  if (!configuration.isResourceLoaded("namespace:" + type.getName())) {
    // 加载 xml
    String xmlResource = type.getName().replace('.', '/') + ".xml";
    // #1347
    InputStream inputStream = type.getResourceAsStream("/" + xmlResource);
    if (inputStream == null) {
      // Search XML mapper that is not in the module but in the classpath.
      try {
        inputStream = Resources.getResourceAsStream(type.getClassLoader(), xmlResource);
      } catch (IOException e2) {
        // ignore, resource is not required
      }
    }
    if (inputStream != null) {
      // 解析 XMLMapper
      XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());
      xmlParser.parse();
    }
  }
}`

说明：加载 xml 部分，默认是获取 class.getName，相当于是 package 路径 +.xml 如下：

类路径 org.apache.UserMapper.class

XML 加载路径 org/apache/UserMapper.xml

应该怎么代码配置 MyBatis？
  @Test
  public void configRegisterMapperTest() {
    Configuration configuration = new Configuration();
    // 构建 Environment
    Environment.Builder builder = new Environment.Builder("11");
    builder.dataSource(new UnpooledDataSource(
      "com.mysql.jdbc.Driver",
      "jdbc:mysql://120.78.218.163:3306/storm_sports",
      "root",
      "@D23d7a3df91cc42"
    ));
    builder.transactionFactory(new JdbcTransactionFactory());
    configuration.setEnvironment(builder.build());
    // 添加 mapper
    configuration.addMapper(UserMapper.class);
    SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(configuration);
    // 开启 sqlSession
    SqlSession sqlSession = factory.openSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    // 查询
    UserDO userDO = userMapper.selectById(1L);
    sqlSession.close();
    System.err.println(userDO);
  }

说明：MyBatis 传统模式采用 mybatis-config.xml 配置，配置过程是：

  1. 解析 mybatis-config.xml 配置文件，转换成一个 Document 对象
  2. 采用 xpath 加载 <configuration> 标签内容
  3. 解析 <configuration> 标签内容
MyBatis 有哪些 StatementType 有哪些？
  // 直接操作sql，不进行预编译，获取数据：$—Statement
  STATEMENT,
  // 预处理，参数，进行预编译，获取数据：#—–PreparedStatement:默认
  PREPARED,
  // 执行存储过程————CallableStatement
  CALLABLE
12/9/2020, 8:54:18 PM