分析了MapperMethod從創(chuàng)建到執(zhí)行的過程,MapperMethod的執(zhí)行包括執(zhí)行sql返回結(jié)果.

在執(zhí)行sql和返回結(jié)果的過程中就會(huì)涉及到參數(shù)類型的轉(zhuǎn)換,這個(gè)過程是通過TypeHandler來處理的.關(guān)于TypeHandler官網(wǎng)有比較詳細(xì)的文檔http://www.mybatis.org/mybatis-3/zh/configuration.html#typeHandlers,文檔主要說明了如何使用TypeHandler,在下面的分析中將重點(diǎn)分析與TypeHandler有關(guān)的源碼.

1.配置

MyBatis有默認(rèn)的類型處理器,如果需要自定義配置也相當(dāng)簡(jiǎn)單,在mybatis-config.xml里添加如下配置:

<typeHandlers>
  <typeHandler handler="org.mybatis.example.ExampleTypeHandler"/>
</typeHandlers>

下面分析配置讀取設(shè)置的過程,在XMLConfigBuilder中

   /**
     * 讀取配置文件組裝configuration
     * @param root 配置文件的configuration節(jié)點(diǎn)
     */
  private void parseConfiguration(XNode root) {    try {      //issue #117 read properties first
      propertiesElement(root.evalNode("properties"));
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      typeAliasesElement(root.evalNode("typeAliases"));
      pluginElement(root.evalNode("plugins"));
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      settingsElement(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);
    }
  }

在以上源碼中有一行

typeHandlerElement(root.evalNode("typeHandlers"));

再來看typeHandlerElement這個(gè)方法

/**
   * 讀取typeHandlers配置并注冊(cè)
   * @param parent 配置文件typeHandlers節(jié)點(diǎn)
   * @throws Exception
   */
  private void typeHandlerElement(XNode parent) throws Exception {    if (parent != null) {      for (XNode child : parent.getChildren()) {        if ("package".equals(child.getName())) {
          String typeHandlerPackage = child.getStringAttribute("name");          typeHandlerRegistry.register(typeHandlerPackage);
        } else {
          String javaTypeName = child.getStringAttribute("javaType");
          String jdbcTypeName = child.getStringAttribute("jdbcType");
          String handlerTypeName = child.getStringAttribute("handler");
          Class<?> javaTypeClass = resolveClass(javaTypeName);
          JdbcType jdbcType = resolveJdbcType(jdbcTypeName);
          Class<?> typeHandlerClass = resolveClass(handlerTypeName);          if (javaTypeClass != null) {            if (jdbcType == null) {              typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
            } else {              typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
            }
          } else {            typeHandlerRegistry.register(typeHandlerClass);
          }
        }
      }
    }
  }

if和else中的代碼邏輯對(duì)應(yīng)了typeHandler的兩種配置方式.最后都會(huì)調(diào)用

typeHandlerRegistry.register()

以上是TypeHandler與TypeHandlerRegistry,Configuration,BaseTypeHandler之間的關(guān)系.

2.設(shè)置參數(shù)

設(shè)置參數(shù)時(shí)先調(diào)用ParameterHandler.setParameters(),然后在setParameters()里獲取相應(yīng)的typeHandler,最后調(diào)用typeHandler.setParameter()

再來看看BaseTypeHandler的setParameter方法

當(dāng)parameter不為null時(shí)調(diào)用的是setNonNullParameter,也就是說子類需要實(shí)現(xiàn)setNonNullParameter

BigIntegerTypeHandler的源碼:

  public void setNonNullParameter(PreparedStatement ps, int i, BigInteger parameter, JdbcType jdbcType) throws SQLException {
    ps.setBigDecimal(i, new BigDecimal(parameter));
  }

至此,TypeHandler的作用已經(jīng)大致分析完畢了.