MyBatis @Param注解的实现

    private boolean hasNamedParams(Method method) {
      final Object[][] paramAnnos = method.getParameterAnnotations();
      for (Object[] paramAnno : paramAnnos) {
        for (Object aParamAnno : paramAnno) {
          if (aParamAnno instanceof Param) {
            return true;
          }
        }
      }
      return false;
    }

    private String getParamNameFromAnnotation(Method method, int i, String paramName) {
      final Object[] paramAnnos = method.getParameterAnnotations()[i];    // 获取第i个参数的注解
      for (Object paramAnno : paramAnnos) {
        if (paramAnno instanceof Param) {
          paramName = ((Param) paramAnno).value();
          break;
        }
      }
      return paramName;
    }

    private SortedMap<Integer, String> getParams(Method method, boolean hasNamedParameters) {
      final SortedMap<Integer, String> params = new TreeMap<Integer, String>();
      final Class<?>[] argTypes = method.getParameterTypes();
      for (int i = 0; i < argTypes.length; i++) {
        if (!RowBounds.class.isAssignableFrom(argTypes[i]) && !ResultHandler.class.isAssignableFrom(argTypes[i])) {
          String paramName = String.valueOf(params.size());    // 参数名，默认为参数的序号
          if (hasNamedParameters) {    //如果有使用@Param注解，则获取注解标注的参数名
            paramName = getParamNameFromAnnotation(method, i, paramName);    // 这里paramName作为参数传进来，表示默认值
          }
          params.put(i, paramName);
        }
      }
      return params;
    }

 public Object convertArgsToSqlCommandParam(Object[] args) {
      final int paramCount = params.size();
      if (args == null || paramCount == 0) {
        return null;
      } else if (!hasNamedParameters && paramCount == 1) {
        return args[params.keySet().iterator().next().intValue()];
      } else {
        final Map<String, Object> param = new ParamMap<Object>();
        int i = 0;
        for (Map.Entry<Integer, String> entry : params.entrySet()) {
          param.put(entry.getValue(), args[entry.getKey().intValue()]);
          // issue #71, add param names as param1, param2...but ensure backward compatibility
          final String genericParamName = "param" + String.valueOf(i + 1);
          if (!param.containsKey(genericParamName)) {
            param.put(genericParamName, args[entry.getKey()]);
          }
          i++;
        }
        return param;
      }
    }

if (!hasNamedParameters && paramCount == 1)

args[params.keySet().iterator().next().intValue()]

final Map<String, Object> param = new ParamMap<Object>();

param.put(entry.getValue(), args[entry.getKey().intValue()]);

final String genericParamName = "param" + String.valueOf(i + 1);
if (!param.containsKey(genericParamName)) {
    param.put(genericParamName, args[entry.getKey()]);
}