code: @Override
      public Map<String, String[]> getParameterMap() {
          if (this.charset.equalsIgnoreCase(this.originCharset)) {
              return super.getParameterMap();
          }
          Map<String, String[]> v = super.getParameterMap();
          if (v.isEmpty()) {
              return v;
          }
          Map<String, String[]> map = new HashMap<String, String[]>();
          try {
              for (String key : v.keySet()) {
                  String[] values = new String[v.get(key).length];
                  int i = 0;
                  for (String value : v.get(key)) {
                      values[i++] = new String(value.getBytes(this.originCharset),
                              this.charset);
                  }
                  map.put(key, values);
              }
          } catch (UnsupportedEncodingException e) {
              e.printStackTrace();
          }
          return map;
      }
docs: 对参数值进行编码