使用Golang+Elastic Search向jQuery传JSON时解析报错：Unexpected token { in JSON

嘿，这问题我太熟了！你碰到的"Unexpected token { in JSON "错误，根源是你从Golang返回的JSON格式完全不符合规范——你把两个独立的JSON对象直接拼在一起了，这根本不是有效的JSON结构，解析器当然会报错。

先看看你当前返回的内容：

{"id":212,"user_id":10,"meta_description":"Plot,G-16, Islamabad,In G-16, Islamabad, Islamabad","property_type":"16","Location1":"Pakistan","Location2":"Islamabad","Location3":null,"Location4":"Islamabad","price":1850000,"bedrooms":0,"bathrooms":0,"add_date":{"Time":"0001-01-01T00:00:00Z","Valid":false}} {"id":213,"user_id":10,"meta_description":"Plot,G-16, Islamabad,In G-16, Islamabad, Islamabad","property_type":"16","Location1":"Pakistan","Location2":"Islamabad","Location3":null,"Location4":"Islamabad","price":1800000,"bedrooms":0,"bathrooms":0,"add_date":{"Time":"0001-01-01T00:00:00Z","Valid":false}}

看到没？两个{...}对象直接连在一起，没有用数组[]包裹，也没有逗号分隔——这在JSON里是绝对不允许的，解析器读到第一个对象结束的}之后，又看到第二个对象的{，就会抛出"Unexpected token {"的错误。

解决方案：把多个JSON对象包裹成数组返回 #

在Golang里，你需要先把从Elasticsearch获取到的所有文档收集到一个切片（slice）里，然后一次性将整个切片编码成JSON数组，而不是逐个编码单个对象。

举个具体的代码例子：

// 先定义对应ES文档的结构体（根据你的实际字段调整）
type Property struct {
    ID              int       `json:"id"`
    UserID          int       `json:"user_id"`
    MetaDescription string    `json:"meta_description"`
    PropertyType    string    `json:"property_type"`
    Location1       string    `json:"Location1"`
    Location2       string    `json:"Location2"`
    Location3       *string   `json:"Location3"` // 用指针类型处理null值
    Location4       string    `json:"Location4"`
    Price           int       `json:"price"`
    Bedrooms        int       `json:"bedrooms"`
    Bathrooms       int       `json:"bathrooms"`
    AddDate         struct {
        Time  time.Time `json:"Time"`
        Valid bool      `json:"Valid"`
    } `json:"add_date"`
}

// 在你的HTTP处理函数里：
func getPropertiesHandler(w http.ResponseWriter, r *http.Request) {
    // 1. 从Elasticsearch查询数据（这里替换成你的实际查询逻辑）
    searchResults, err := esClient.Search(...)
    if err != nil {
        http.Error(w, "Failed to fetch data from Elasticsearch", http.StatusInternalServerError)
        return
    }

    // 2. 把所有查询到的文档收集到切片中
    var properties []Property
    for _, hit := range searchResults.Hits.Hits {
        var prop Property
        if err := json.Unmarshal(hit.Source, &prop); err != nil {
            http.Error(w, "Failed to parse document", http.StatusInternalServerError)
            return
        }
        properties = append(properties, prop)
    }

    // 3. 设置正确的Content-Type头，然后一次性编码整个切片为JSON数组
    w.Header().Set("Content-Type", "application/json")
    if err := json.NewEncoder(w).Encode(properties); err != nil {
        http.Error(w, "Failed to encode JSON", http.StatusInternalServerError)
        return
    }
}

这样修改后，你返回的JSON会变成标准的数组格式：

[
    {"id":212,"user_id":10,"meta_description":"Plot,G-16, Islamabad,In G-16, Islamabad, Islamabad","property_type":"16","Location1":"Pakistan","Location2":"Islamabad","Location3":null,"Location4":"Islamabad","price":1850000,"bedrooms":0,"bathrooms":0,"add_date":{"Time":"0001-01-01T00:00:00Z","Valid":false}},
    {"id":213,"user_id":10,"meta_description":"Plot,G-16, Islamabad,In G-16, Islamabad, Islamabad","property_type":"16","Location1":"Pakistan","Location2":"Islamabad","Location3":null,"Location4":"Islamabad","price":1800000,"bedrooms":0,"bathrooms":0,"add_date":{"Time":"0001-01-01T00:00:00Z","Valid":false}}
]

这个格式完全符合JSON规范，jQuery的$.getJSON()或者JSON.parse()都能正常解析，不会再报错啦！

内容的提问来源于stack exchange，提问作者Sarmad Nazir