Golang json 解析

背景：
最近在用iris做web端的時候，遇到了這麼一個問題，前端傳過來的json串如下：

{
    "Name": "jiankunking",
    "Age": 12,
    "BlogArticles": {
        "one": {
            "Detail": "csdn blog",
            "Author": "jiankunking",
            "Urls": {
                "1": "http://blog.csdn.net/jiankunking/article/details/52143504",
                "2": "http://blog.csdn.net/jiankunking/article/details/52673302",
                "3": "http://blog.csdn.net/jiankunking/article/details/45479105"
            }
        },
        "two": {
            "Detail": "CSDN BLOG",
            "Author": "JIANKUNKING",
            "Urls": {
                "1": "http://blog.csdn.net/jiankunking/article/details/52684722",
                "2": "http://blog.csdn.net/jiankunking/article/details/78808978"
            }
        }
    }
}

我用如下的結構接收：

    type Person struct {
        Name         string
        Age          int
        BlogArticles map[string]interface{}
    }
    type BlogArticle struct {
        Detail string
        Author string
        Urls   map[string]string
    }

從json結構來看，結構Person中BlogArticles map值的結構均符合 結構BlogArticle ，那我是不是可以這麼做呢？

blogArticle3 := person.BlogArticles["one"].(BlogArticle)
//此時輸出person.BlogArticles["one"]型別，可知，
//person.BlogArticles["one"]是map[string]interface {}
//雖然，看起來結構一樣，但map[string]interface {}與BlogArticle卻無法轉換

答案是否定的，錯誤資訊如下：

panic: interface conversion: interface {} is map[string]interface {}, not main.BlogArticle

那麼正確的做法應該如何處理呢？在接收資料的時候，用如下結構接收：

type BlogArticle struct {
        Detail string
        Author string
        Urls   map[string]string
    }

    type PersonCorrect struct {
        Name         string
        Age          int
        BlogArticles map[string]BlogArticle
    }

這時輸出person.BlogArticles[“one”]的型別可知：

fmt.Println(typeof(personCorrect.BlogArticles["one"]))
//結果
//main.BlogArticle

演示程式碼如下：
https://github.com/jiankunking/backups/blob/master/decode.go

那麼，”encoding/json”到底是怎麼反序列化的呢？
在decode結構註釋中，找到以下介紹：

// Unmarshal parses the JSON-encoded data and stores the result
// in the value pointed to by v.
//
// Unmarshal uses the inverse of the encodings that
// Marshal uses, allocating maps, slices, and pointers as necessary,
// with the following additional rules:
//
// To unmarshal JSON into a pointer, Unmarshal first handles the case of
// the JSON being the JSON literal null. In that case, Unmarshal sets
// the pointer to nil. Otherwise, Unmarshal unmarshals the JSON into
// the value pointed at by the pointer. If the pointer is nil, Unmarshal
// allocates a new value for it to point to.
//
// To unmarshal JSON into a value implementing the Unmarshaler interface,
// Unmarshal calls that value's UnmarshalJSON method, including
// when the input is a JSON null.
// Otherwise, if the value implements encoding.TextUnmarshaler
// and the input is a JSON quoted string, Unmarshal calls that value's
// UnmarshalText method with the unquoted form of the string.
//
// To unmarshal JSON into a struct, Unmarshal matches incoming object
// keys to the keys used by Marshal (either the struct field name or its tag),
// preferring an exact match but also accepting a case-insensitive match.
// Unmarshal will only set exported fields of the struct.
//
// To unmarshal JSON into an interface value,
// Unmarshal stores one of these in the interface value:
//
//  bool, for JSON booleans
//  float64, for JSON numbers
//  string, for JSON strings
//  []interface{}, for JSON arrays
//  map[string]interface{}, for JSON objects
//  nil for JSON null
//
// To unmarshal a JSON array into a slice, Unmarshal resets the slice length
// to zero and then appends each element to the slice.
// As a special case, to unmarshal an empty JSON array into a slice,
// Unmarshal replaces the slice with a new empty slice.
//
// To unmarshal a JSON array into a Go array, Unmarshal decodes
// JSON array elements into corresponding Go array elements.
// If the Go array is smaller than the JSON array,
// the additional JSON array elements are discarded.
// If the JSON array is smaller than the Go array,
// the additional Go array elements are set to zero values.
//
// To unmarshal a JSON object into a map, Unmarshal first establishes a map to
// use. If the map is nil, Unmarshal allocates a new map. Otherwise Unmarshal
// reuses the existing map, keeping existing entries. Unmarshal then stores
// key-value pairs from the JSON object into the map. The map's key type must
// either be a string, an integer, or implement encoding.TextUnmarshaler.
//
// If a JSON value is not appropriate for a given target type,
// or if a JSON number overflows the target type, Unmarshal
// skips that field and completes the unmarshaling as best it can.
// If no more serious errors are encountered, Unmarshal returns
// an UnmarshalTypeError describing the earliest such error.
//
// The JSON null value unmarshals into an interface, map, pointer, or slice
// by setting that Go value to nil. Because null is often used in JSON to mean
// ``not present,'' unmarshaling a JSON null into any other Go type has no effect
// on the value and produces no error.
//
// When unmarshaling quoted strings, invalid UTF-8 or
// invalid UTF-16 surrogate pairs are not treated as an error.
// Instead, they are replaced by the Unicode replacement
// character U+FFFD.
//

原始碼地址如下：
https://github.com/golang/go/blob/release-branch.go1.8/src/encoding/json/decode.go

但並未說明當unmarshal a JSON object into a map時，如果map中的value是interface{}時，該如何處理。
具體處理程式碼可以看原始碼func Unmarshal(data []byte, v interface{}) error {}處理的整個流程。

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作者：jiankunking 出處：http://blog.csdn.net/jiankunking