Mybatis源碼分析:MapperMethod中內部靜態類MethodSignature的作用

MethodSignature分析

　　MethodSignature為MapperMethod類提供了三個作用,獲取待執行方法中的參數和@Param注解標注的參數名,獲取標注有@MapKey的參數(@Mapkey作用在后續會講到),方法的返回類型,獲取SELECT操作時必要的標志位。以下是MethodSignature的所有屬性。

• private final boolean returnsMany;//是否多值查詢
• private final boolean returnsMap;//是否map查詢
• private final boolean returnsVoid;//是否void查詢
• private final boolean returnsCursor;//是否游標查詢
• private final Class<?> returnType; //返回類型
• private final String mapKey;//獲取mapKey的值
• private final Integer resultHandlerIndex;
• private final Integer rowBoundsIndex;
• private final ParamNameResolver paramNameResolver; //參數解析器

　　觀察下列的代碼,構造器首先獲取返回類型,這個值通過類型參數解析器來獲取入參mapperInterface本身及所有的父類和所有的接口來查找所要返回的類型,Mybatis提供了三種類型實現ParameterizedType,TypeVariable,GenericArrayType。通過返回的類型值來判定后續的SElECT將要做哪種查詢,void查詢,Map查詢，游標查詢,多值查詢,這里就會給相關的屬性進行打標,在mapperMethod執行exeute()方法時便會進行判斷。構造器還會檢查待執行的Mapper方法是否標注有@Mapkey的注解,如果有這意味着返回的結果類型是一個Map。

   public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
        //解析返回的類型 ParameterizedType,TypeVariable,GenericArrayType
      Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
      if (resolvedReturnType instanceof Class<?>) {
        this.returnType = (Class<?>) resolvedReturnType;
      } else if (resolvedReturnType instanceof ParameterizedType) {
        this.returnType = (Class<?>) ((ParameterizedType) resolvedReturnType).getRawType();
      } else {
        this.returnType = method.getReturnType();
      }
      this.returnsVoid = void.class.equals(this.returnType);
      //是否是集合或者數組類型
      this.returnsMany = configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray();
      //判斷是否是游標類型
      this.returnsCursor = Cursor.class.equals(this.returnType);
      //獲取MapKey注解
      this.mapKey = getMapKey(method);
      //判斷mapkey是否不為NULL
      this.returnsMap = this.mapKey != null;
      this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
      this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
      //初始化參數名解析器
      this.paramNameResolver = new ParamNameResolver(configuration, method);
    }