wx.downloadFile的url直接写完整的可以下载打开，使用拼接的url返回的文件就不对了，下面这个是that.data.path打印的数据,这两个拼接是一样的，但为啥就不行呢？url: 'http://localhost:8080/mycode_war_exploded/upload/a29b135e291f481f8632b5478ed8dfa4.pdf', //这个就能打开

  preview:function(){
    var that = this;
    wx.downloadFile({
      url: uriUtils.BASE_URL_UPLOAD + that.data.path,
      success: function (res) {
        console.log(res);
        var filePath = res.tempFilePath
        console.log(filePath);
        wx.openDocument({
          filePath: filePath,
          success: function (res) {
            console.log("打开文档成功")
            console.log(res);
          },
          fail: function (res) {
            console.log("fail");
            console.log(res)
          },
          complete: function (res) {
           console.log("complete");
            console.log(res)
          }    
        })
      }
    })
  },