Format and remove 07.2.md spaces
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vCaesar
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zh/07.2.md
220
zh/07.2.md
@@ -4,7 +4,7 @@ JSON（Javascript Object Notation）是一种轻量级的数据交换语言，
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前一小节的运维的例子用json来表示，结果描述如下：
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```json
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{"servers":[{"serverName":"Shanghai_VPN","serverIP":"127.0.0.1"},{"serverName":"Beijing_VPN","serverIP":"127.0.0.2"}]}
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{"servers":[{"serverName":"Shanghai_VPN","serverIP":"127.0.0.1"},{"serverName":"Beijing_VPN","serverIP":"127.0.0.2"}]}
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```
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本小节余下的内容将以此JSON数据为基础，来介绍go语言的json包对JSON数据的编、解码。
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## 解析JSON
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@@ -13,33 +13,33 @@ JSON（Javascript Object Notation）是一种轻量级的数据交换语言，
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假如有了上面的JSON串，那么我们如何来解析这个JSON串呢？Go的JSON包中有如下函数
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```Go
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func Unmarshal(data []byte, v interface{}) error
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func Unmarshal(data []byte, v interface{}) error
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```
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通过这个函数我们就可以实现解析的目的，详细的解析例子请看如下代码：
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```Go
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package main
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package main
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import (
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"encoding/json"
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"fmt"
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)
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import (
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"encoding/json"
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"fmt"
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)
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type Server struct {
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ServerName string
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ServerIP string
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}
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type Server struct {
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ServerName string
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ServerIP string
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}
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type Serverslice struct {
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Servers []Server
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}
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type Serverslice struct {
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Servers []Server
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}
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func main() {
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var s Serverslice
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str := `{"servers":[{"serverName":"Shanghai_VPN","serverIP":"127.0.0.1"},{"serverName":"Beijing_VPN","serverIP":"127.0.0.2"}]}`
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json.Unmarshal([]byte(str), &s)
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fmt.Println(s)
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}
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func main() {
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var s Serverslice
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str := `{"servers":[{"serverName":"Shanghai_VPN","serverIP":"127.0.0.1"},{"serverName":"Beijing_VPN","serverIP":"127.0.0.2"}]}`
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json.Unmarshal([]byte(str), &s)
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fmt.Println(s)
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}
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```
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在上面的示例代码中，我们首先定义了与json数据对应的结构体，数组对应slice，字段名对应JSON里面的KEY，在解析的时候，如何将json数据与struct字段相匹配呢？例如JSON的key是`Foo`，那么怎么找对应的字段呢？
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@@ -62,71 +62,71 @@ JSON（Javascript Object Notation）是一种轻量级的数据交换语言，
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现在我们假设有如下的JSON数据
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```Go
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b := []byte(`{"Name":"Wednesday","Age":6,"Parents":["Gomez","Morticia"]}`)
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b := []byte(`{"Name":"Wednesday","Age":6,"Parents":["Gomez","Morticia"]}`)
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```
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如果在我们不知道他的结构的情况下，我们把他解析到interface{}里面
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```Go
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var f interface{}
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err := json.Unmarshal(b, &f)
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var f interface{}
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err := json.Unmarshal(b, &f)
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```
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这个时候f里面存储了一个map类型，他们的key是string，值存储在空的interface{}里
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```Go
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f = map[string]interface{}{
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"Name": "Wednesday",
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"Age": 6,
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"Parents": []interface{}{
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"Gomez",
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"Morticia",
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},
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}
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f = map[string]interface{}{
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"Name": "Wednesday",
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"Age": 6,
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"Parents": []interface{}{
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"Gomez",
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"Morticia",
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},
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}
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```
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那么如何来访问这些数据呢？通过断言的方式：
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```Go
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m := f.(map[string]interface{})
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m := f.(map[string]interface{})
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```
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通过断言之后，你就可以通过如下方式来访问里面的数据了
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```Go
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for k, v := range m {
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switch vv := v.(type) {
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case string:
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fmt.Println(k, "is string", vv)
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case int:
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fmt.Println(k, "is int", vv)
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case float64:
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fmt.Println(k,"is float64",vv)
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case []interface{}:
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fmt.Println(k, "is an array:")
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for i, u := range vv {
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fmt.Println(i, u)
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}
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default:
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fmt.Println(k, "is of a type I don't know how to handle")
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for k, v := range m {
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switch vv := v.(type) {
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case string:
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fmt.Println(k, "is string", vv)
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case int:
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fmt.Println(k, "is int", vv)
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case float64:
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fmt.Println(k,"is float64",vv)
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case []interface{}:
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fmt.Println(k, "is an array:")
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for i, u := range vv {
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fmt.Println(i, u)
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}
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default:
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fmt.Println(k, "is of a type I don't know how to handle")
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}
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}
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```
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通过上面的示例可以看到，通过interface{}与type assert的配合，我们就可以解析未知结构的JSON数了。
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上面这个是官方提供的解决方案，其实很多时候我们通过类型断言，操作起来不是很方便，目前bitly公司开源了一个叫做`simplejson`的包,在处理未知结构体的JSON时相当方便，详细例子如下所示：
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```Go
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js, err := NewJson([]byte(`{
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"test": {
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"array": [1, "2", 3],
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"int": 10,
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"float": 5.150,
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"bignum": 9223372036854775807,
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"string": "simplejson",
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"bool": true
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}
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}`))
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js, err := NewJson([]byte(`{
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"test": {
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"array": [1, "2", 3],
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"int": 10,
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"float": 5.150,
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"bignum": 9223372036854775807,
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"string": "simplejson",
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"bool": true
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}
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}`))
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arr, _ := js.Get("test").Get("array").Array()
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i, _ := js.Get("test").Get("int").Int()
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ms := js.Get("test").Get("string").MustString()
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arr, _ := js.Get("test").Get("array").Array()
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i, _ := js.Get("test").Get("int").Int()
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ms := js.Get("test").Get("string").MustString()
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```
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可以看到，使用这个库操作JSON比起官方包来说，简单的多,详细的请参考如下地址：https://github.com/bitly/go-simplejson
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@@ -135,55 +135,55 @@ JSON（Javascript Object Notation）是一种轻量级的数据交换语言，
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我们开发很多应用的时候，最后都是要输出JSON数据串，那么如何来处理呢？JSON包里面通过`Marshal`函数来处理，函数定义如下：
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```Go
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func Marshal(v interface{}) ([]byte, error)
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func Marshal(v interface{}) ([]byte, error)
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```
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假设我们还是需要生成上面的服务器列表信息，那么如何来处理呢？请看下面的例子：
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```Go
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package main
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package main
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import (
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"encoding/json"
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"fmt"
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)
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import (
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"encoding/json"
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"fmt"
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)
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type Server struct {
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ServerName string
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ServerIP string
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}
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type Serverslice struct {
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Servers []Server
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}
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func main() {
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var s Serverslice
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s.Servers = append(s.Servers, Server{ServerName: "Shanghai_VPN", ServerIP: "127.0.0.1"})
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s.Servers = append(s.Servers, Server{ServerName: "Beijing_VPN", ServerIP: "127.0.0.2"})
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b, err := json.Marshal(s)
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if err != nil {
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fmt.Println("json err:", err)
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}
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fmt.Println(string(b))
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type Server struct {
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ServerName string
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ServerIP string
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}
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type Serverslice struct {
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Servers []Server
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}
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func main() {
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var s Serverslice
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s.Servers = append(s.Servers, Server{ServerName: "Shanghai_VPN", ServerIP: "127.0.0.1"})
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s.Servers = append(s.Servers, Server{ServerName: "Beijing_VPN", ServerIP: "127.0.0.2"})
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b, err := json.Marshal(s)
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if err != nil {
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fmt.Println("json err:", err)
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}
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fmt.Println(string(b))
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}
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```
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输出如下内容：
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```json
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{"Servers":[{"ServerName":"Shanghai_VPN","ServerIP":"127.0.0.1"},{"ServerName":"Beijing_VPN","ServerIP":"127.0.0.2"}]}
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{"Servers":[{"ServerName":"Shanghai_VPN","ServerIP":"127.0.0.1"},{"ServerName":"Beijing_VPN","ServerIP":"127.0.0.2"}]}
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```
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我们看到上面的输出字段名的首字母都是大写的，如果你想用小写的首字母怎么办呢？把结构体的字段名改成首字母小写的？JSON输出的时候必须注意，只有导出的字段才会被输出，如果修改字段名，那么就会发现什么都不会输出，所以必须通过struct tag定义来实现：
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```Go
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type Server struct {
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ServerName string `json:"serverName"`
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ServerIP string `json:"serverIP"`
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}
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type Server struct {
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ServerName string `json:"serverName"`
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ServerIP string `json:"serverIP"`
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}
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type Serverslice struct {
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Servers []Server `json:"servers"`
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}
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type Serverslice struct {
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Servers []Server `json:"servers"`
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}
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```
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通过修改上面的结构体定义，输出的JSON串就和我们最开始定义的JSON串保持一致了。
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@@ -198,32 +198,32 @@ JSON（Javascript Object Notation）是一种轻量级的数据交换语言，
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举例来说：
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```Go
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type Server struct {
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// ID 不会导出到JSON中
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ID int `json:"-"`
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type Server struct {
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// ID 不会导出到JSON中
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ID int `json:"-"`
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// ServerName2 的值会进行二次JSON编码
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ServerName string `json:"serverName"`
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ServerName2 string `json:"serverName2,string"`
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// ServerName2 的值会进行二次JSON编码
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ServerName string `json:"serverName"`
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ServerName2 string `json:"serverName2,string"`
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// 如果 ServerIP 为空，则不输出到JSON串中
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ServerIP string `json:"serverIP,omitempty"`
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}
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// 如果 ServerIP 为空，则不输出到JSON串中
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ServerIP string `json:"serverIP,omitempty"`
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}
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s := Server {
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ID: 3,
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ServerName: `Go "1.0" `,
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ServerName2: `Go "1.0" `,
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ServerIP: ``,
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}
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b, _ := json.Marshal(s)
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os.Stdout.Write(b)
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s := Server {
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ID: 3,
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ServerName: `Go "1.0" `,
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ServerName2: `Go "1.0" `,
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ServerIP: ``,
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}
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b, _ := json.Marshal(s)
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os.Stdout.Write(b)
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```
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会输出以下内容：
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```json
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{"serverName":"Go \"1.0\" ","serverName2":"\"Go \\\"1.0\\\" \""}
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{"serverName":"Go \"1.0\" ","serverName2":"\"Go \\\"1.0\\\" \""}
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```
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Marshal函数只有在转换成功的时候才会返回数据，在转换的过程中我们需要注意几点：
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