我现在正在使用 Martini 和 AppEngine/Go 进行编码。

我想使用内存缓存来提供 JSON 数据。 但是返回的是无效的JSON格式，为什么返回的是“null”？

null{"results":[{"Title":"Nikkei225","PriceTime":"2014-04-25 06:28:00 UTC","Price":"14,429.26","Diff":"＋24.27(0.1%)"},{"Title":"USD/JPY","PriceTime":"2014-04-25 20:49:00 UTC","Price":"102.12-102.16","Diff":"－0.15(-0.1%)"},{"Title":"EURO/JPY","PriceTime":"2014-04-25 20:49:00 UTC","Price":"141.28-141.32","Diff":"－0.19(-0.1%)"},{"Title":"EURO/USD","PriceTime":"2014-04-25 20:48:00 UTC","Price":"1.3833-1.3836","Diff":"＋0.0002(0.0%)"},{"Title":"USD/CNY","PriceTime":"2014-04-25 20:48:00 UTC","Price":"6.2536-6.2546","Diff":"＋0.0063(0.1%)"},{"Title":"DJIA","PriceTime":"2014-04-25 07:29:00 UTC","Price":"16,361.46","Diff":"－140.19(-0.8%)"},{"Title":"Nasdaq","PriceTime":"2014-04-25 07:00:00 UTC","Price":"4,075.561","Diff":"－72.777(-1.7%)"},{"Title":"FTSE100","PriceTime":"2014-04-25 07:35:00 UTC","Price":"6,685.69","Diff":"－17.31(-0.2%)"}]} 

控制台如下所示:

http: multiple response.WriteHeader calls 

我的代码如下。
从缓存中检索:

    c := appengine.NewContext(req) 
    memcacheKey := "markets" 
    results := []Result{} 
    cachedItem, getCacheErr := memcache.JSON.Get(c, memcacheKey,&map[string]interface{}{"results": results}) 
    if getCacheErr != nil && getCacheErr != memcache.ErrCacheMiss { 
        c.Infof("get cache error") 
    } 
    if getCacheErr == nil { 
        c.Infof("cached data found") 
        c.Infof("cached data: %v",cachedItem.Value) 
        r.JSON(200, cachedItem.Object) 
    } else { 
        c.Infof("cached data not found") 
    } 

设置为内存缓存:

    client := urlfetch.Client(c) 
    resp, err := client.Get("http://www.nikkei.com/markets/kaigai/worldidx.aspx") 
    if err != nil { 
        http.Error(w, err.Error(), http.StatusInternalServerError) 
    } 
    indexes := Indexes() 
    doc, _ := goquery.NewDocumentFromResponse(resp) 
    doc.Find("div.mk-world_market div table tr").Each(func(_ int, s *goquery.Selection) { 
            title := s.Find("th").Text() 
            title = strings.Trim(strings.Replace(title,"※","",-1)," ") 
            if val,ok := indexes[title]; ok { 
                price := s.Find("th").Next().Text() 
                diff := s.Find("td:nth-child(3)").Text() 
                pricetime := s.Find("td:nth-child(4)").Text() 
                t := time.Now() 
                pricetime = StringToTime(pricetime,t) 
                result := Result{val,pricetime,price,diff} 
                results = append(results,result) 
            } 
    }) 
    item := &memcache.Item{ 
        Key:memcacheKey, 
        Object: &map[string]interface{}{"results": results}, 
    } 
    setErr := memcache.JSON.Set(c, item) 
    if setErr != nil { 
        c.Infof("set error: %v",setErr) 
    } 

我的代码有什么问题？

请您参考如下方法:

self 解决:

下面是我想做的。

    m.Get("/api/Markets", func(w http.ResponseWriter,r render.Render,req *http.Request) { 
    c := appengine.NewContext(req) 
    memcache_key := "markets" 
    var item_list []Result 
    results := []Result{} 
    _, get_cache_err := memcache.JSON.Get(c,memcache_key,&item_list) 
    if get_cache_err != nil && get_cache_err != memcache.ErrCacheMiss { 
        c.Infof("get cache error") 
    } 
    if get_cache_err == nil { 
        c.Infof("cached data found") 
        c.Infof("cached data: %v",item_list) 
        results = item_list 
    } else { 
        c.Infof("cached data not found") 
        client := urlfetch.Client(c) 
        resp, err := client.Get("http://www.nikkei.com/markets/kaigai/worldidx.aspx") 
        if err != nil { 
            http.Error(w, err.Error(), http.StatusInternalServerError) 
        } 
        indexes := Indexes() 
        doc, _ := goquery.NewDocumentFromResponse(resp) 
        doc.Find("div.mk-world_market div table tr").Each(func(_ int, s *goquery.Selection) { 
            title := s.Find("th").Text() 
            title = strings.Trim(strings.Replace(title,"※","",-1)," ") 
            if val,ok := indexes[title]; ok { 
                price := s.Find("th").Next().Text() 
                diff := s.Find("td:nth-child(3)").Text() 
                pricetime := s.Find("td:nth-child(4)").Text() 
                t := time.Now() 
                pricetime = StringToTime(pricetime,t) 
                result := Result{val,pricetime,price,diff} 
                results = append(results,result) 
            } 
        }) 
        item_list = results 
        item := &memcache.Item{ 
            Key:memcache_key, 
            Object: &item_list, 
        } 
        setErr := memcache.JSON.Set(c, item) 
        if setErr != nil { 
            c.Infof("set error: %v",setErr) 
        } 
    } 
    r.JSON(200, map[string]interface{}{"results": item_list}) 
})