聊聊mybatis的ParamNameResolver

序

在mybatis的interceptor获取MapperMethod.ParamMap这种参数类型时，经常会多出param1，param2，collection，list，array这些参数，这些不是接口自己定义的，而是ParamNameResolver自动添加的

ParamNameResolver

org/apache/ibatis/reflection/ParamNameResolver.java

public class ParamNameResolver {

  public static final String GENERIC_NAME_PREFIX = "param";

  /**
   * 

   * 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,
   * ...).
   * 
   *
   * @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 param = new ParamMap<>();
      int i = 0;
      for (Map.Entry 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方法针对单个参数没有加@Param的场景会调用wrapToMapIfCollection，其他的则使用param1,param2这种，这里用了contains，也就是如果本身命名就有包含param1,param2这种则不会添加

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