深入理解mybatis的ParamNameResolver

更新時間：2023年08月30日 10:43:09 作者：hello_ejb3

ParamNameResolver是 MyBatis 中的一個重要組件,它為 MyBatis 提供了一種方便的方式來獲取方法參數(shù)的名稱,本文主要介紹了深入理解mybatis的ParamNameResolver,具有一定的參考價值,感興趣的可以了解一下

序

在mybatis的interceptor獲取MapperMethod.ParamMap這種參數(shù)類型時，經常會多出param1，param2，collection，list，array這些參數(shù)，這些不是接口自己定義的，而是ParamNameResolver自動添加的

ParamNameResolver

org/apache/ibatis/reflection/ParamNameResolver.java

public class ParamNameResolver {
  public static final String GENERIC_NAME_PREFIX = "param";
  /**
   * <p>
   * A single non-special parameter is returned without a name.
   * Multiple parameters are named using the naming rule.
   * In addition to the default names, this method also adds the generic names (param1, param2,
   * ...).
   * </p>
   *
   * @param args
   *          the args
   * @return the named params
   */
  public Object getNamedParams(Object[] args) {
    final int paramCount = names.size();
    if (args == null || paramCount == 0) {
      return null;
    } else if (!hasParamAnnotation && paramCount == 1) {
      Object value = args[names.firstKey()];
      return wrapToMapIfCollection(value, useActualParamName ? names.get(0) : null);
    } else {
      final Map<String, Object> param = new ParamMap<>();
      int i = 0;
      for (Map.Entry<Integer, String> entry : names.entrySet()) {
        param.put(entry.getValue(), args[entry.getKey()]);
        // add generic param names (param1, param2, ...)
        final String genericParamName = GENERIC_NAME_PREFIX + (i + 1);
        // ensure not to overwrite parameter named with @Param
        if (!names.containsValue(genericParamName)) {
          param.put(genericParamName, args[entry.getKey()]);
        }
        i++;
      }
      return param;
    }
  }
  //......
}

getNamedParams方法針對單個參數(shù)沒有加@Param的場景會調用wrapToMapIfCollection，其他的則使用param1,param2這種，這里用了contains，也就是如果本身命名就有包含param1,param2這種則不會添加

wrapToMapIfCollection

org/apache/ibatis/reflection/ParamNameResolver.java

  /**
   * Wrap to a {@link ParamMap} if object is {@link Collection} or array.
   *
   * @param object a parameter object
   * @param actualParamName an actual parameter name
   *                        (If specify a name, set an object to {@link ParamMap} with specified name)
   * @return a {@link ParamMap}
   * @since 3.5.5
   */
  public static Object wrapToMapIfCollection(Object object, String actualParamName) {
    if (object instanceof Collection) {
      ParamMap<Object> map = new ParamMap<>();
      map.put("collection", object);
      if (object instanceof List) {
        map.put("list", object);
      }
      Optional.ofNullable(actualParamName).ifPresent(name -> map.put(name, object));
      return map;
    } else if (object != null && object.getClass().isArray()) {
      ParamMap<Object> map = new ParamMap<>();
      map.put("array", object);
      Optional.ofNullable(actualParamName).ifPresent(name -> map.put(name, object));
      return map;
    }
    return object;
  }