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<title>Go в примерах: JSON</title>
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<div class="example" id="json">
<h2><a href="./">Go в примерах</a>: JSON</h2>
<table>
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<td class="docs">
<p>Go предлагает встроенную поддержку кодирования и
декодирования JSON, в том числе встроенных и
пользовательских типов данных.</p>
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<td class="code leading">
<a href="http://play.golang.org/p/Lky4Hyyl2-t" target="_blank"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
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<td class="code leading">
<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
<span class="s">&quot;encoding/json&quot;</span>
<span class="s">&quot;fmt&quot;</span>
<span class="s">&quot;os&quot;</span>
<span class="p">)</span>
</pre></div>
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<td class="docs">
<p>Мы будем использовать эти две структуры, для демонстрации
кодирования и декодирования.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">type</span> <span class="nx">response1</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">Page</span> <span class="kt">int</span>
<span class="nx">Fruits</span> <span class="p">[]</span><span class="kt">string</span>
<span class="p">}</span>
</pre></div>
</td>
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<td class="docs">
<p>Только экспортируемые поля могут быть кодированы и
декодированы в JSON. Поля должны начинаться с
заглавной буквы.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">type</span> <span class="nx">response2</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">Page</span> <span class="kt">int</span> <span class="s">`json:&quot;page&quot;`</span>
<span class="nx">Fruits</span> <span class="p">[]</span><span class="kt">string</span> <span class="s">`json:&quot;fruits&quot;`</span>
<span class="p">}</span>
</pre></div>
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<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>
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<td class="docs">
<p>Для начала мы рассмотрим кодирование данных в
JSON строку. Вот несколько примеров для простых
типов данных.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">bolB</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">Marshal</span><span class="p">(</span><span class="kc">true</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">bolB</span><span class="p">))</span>
</pre></div>
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<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">intB</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">Marshal</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">intB</span><span class="p">))</span>
</pre></div>
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<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">fltB</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">Marshal</span><span class="p">(</span><span class="mf">2.34</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">fltB</span><span class="p">))</span>
</pre></div>
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<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">strB</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">Marshal</span><span class="p">(</span><span class="s">&quot;gopher&quot;</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">strB</span><span class="p">))</span>
</pre></div>
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<td class="docs">
<p>А вот примеры для срезов и карт, которые кодируются
в JSON массивы и объекты, как мы и ожидаем.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">slcD</span> <span class="o">:=</span> <span class="p">[]</span><span class="kt">string</span><span class="p">{</span><span class="s">&quot;apple&quot;</span><span class="p">,</span> <span class="s">&quot;peach&quot;</span><span class="p">,</span> <span class="s">&quot;pear&quot;</span><span class="p">}</span>
<span class="nx">slcB</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">Marshal</span><span class="p">(</span><span class="nx">slcD</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">slcB</span><span class="p">))</span>
</pre></div>
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<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">mapD</span> <span class="o">:=</span> <span class="kd">map</span><span class="p">[</span><span class="kt">string</span><span class="p">]</span><span class="kt">int</span><span class="p">{</span><span class="s">&quot;apple&quot;</span><span class="p">:</span> <span class="mi">5</span><span class="p">,</span> <span class="s">&quot;lettuce&quot;</span><span class="p">:</span> <span class="mi">7</span><span class="p">}</span>
<span class="nx">mapB</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">Marshal</span><span class="p">(</span><span class="nx">mapD</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">mapB</span><span class="p">))</span>
</pre></div>
</td>
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<tr>
<td class="docs">
<p>Пакет JSON может автоматически кодировать ваши
пользовательские типы данных. Он будет включать
только экспортируемые поля в закодированный
вывод и по умолчанию будет использовать эти
имена в качестве ключей JSON.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">res1D</span> <span class="o">:=</span> <span class="o">&amp;</span><span class="nx">response1</span><span class="p">{</span>
<span class="nx">Page</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span>
<span class="nx">Fruits</span><span class="p">:</span> <span class="p">[]</span><span class="kt">string</span><span class="p">{</span><span class="s">&quot;apple&quot;</span><span class="p">,</span> <span class="s">&quot;peach&quot;</span><span class="p">,</span> <span class="s">&quot;pear&quot;</span><span class="p">}}</span>
<span class="nx">res1B</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">Marshal</span><span class="p">(</span><span class="nx">res1D</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">res1B</span><span class="p">))</span>
</pre></div>
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<tr>
<td class="docs">
<p>Вы можете использовать теги в объявлениях
структурных полей для настройки кодированных имен
ключей JSON. Проверьте определение <code>response2</code>
выше, чтобы увидеть пример таких тегов.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">res2D</span> <span class="o">:=</span> <span class="o">&amp;</span><span class="nx">response2</span><span class="p">{</span>
<span class="nx">Page</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span>
<span class="nx">Fruits</span><span class="p">:</span> <span class="p">[]</span><span class="kt">string</span><span class="p">{</span><span class="s">&quot;apple&quot;</span><span class="p">,</span> <span class="s">&quot;peach&quot;</span><span class="p">,</span> <span class="s">&quot;pear&quot;</span><span class="p">}}</span>
<span class="nx">res2B</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">Marshal</span><span class="p">(</span><span class="nx">res2D</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">res2B</span><span class="p">))</span>
</pre></div>
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<td class="docs">
<p>Теперь давайте рассмотрим декодирование данных
JSON в значения Go. Вот пример для общей
структуры данных.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">byt</span> <span class="o">:=</span> <span class="p">[]</span><span class="nb">byte</span><span class="p">(</span><span class="s">`{&quot;num&quot;:6.13,&quot;strs&quot;:[&quot;a&quot;,&quot;b&quot;]}`</span><span class="p">)</span>
</pre></div>
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<td class="docs">
<p>Нам нужно предоставить переменную, в которую пакет
JSON может поместить декодированные данные.
`map[string]interface{} будет содержать карту
строк для произвольных типов данных.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="kd">var</span> <span class="nx">dat</span> <span class="kd">map</span><span class="p">[</span><span class="kt">string</span><span class="p">]</span><span class="kd">interface</span><span class="p">{}</span>
</pre></div>
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<td class="docs">
<p>Вот фактическое декодирование и проверка на наличие
ошибок.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="k">if</span> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">Unmarshal</span><span class="p">(</span><span class="nx">byt</span><span class="p">,</span> <span class="o">&amp;</span><span class="nx">dat</span><span class="p">);</span> <span class="nx">err</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
<span class="nb">panic</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span>
<span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">dat</span><span class="p">)</span>
</pre></div>
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<td class="docs">
<p>Чтобы использовать значения в декодированной карте,
нам нужно преобразовать их в соответствующий тип.
Например, здесь мы конвертируем значение из <code>num</code>
в ожидаемый тип <code>float64</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">num</span> <span class="o">:=</span> <span class="nx">dat</span><span class="p">[</span><span class="s">&quot;num&quot;</span><span class="p">].(</span><span class="kt">float64</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">num</span><span class="p">)</span>
</pre></div>
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<td class="docs">
<p>Доступ к вложенным данным требует ряда преобразований.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">strs</span> <span class="o">:=</span> <span class="nx">dat</span><span class="p">[</span><span class="s">&quot;strs&quot;</span><span class="p">].([]</span><span class="kd">interface</span><span class="p">{})</span>
<span class="nx">str1</span> <span class="o">:=</span> <span class="nx">strs</span><span class="p">[</span><span class="mi">0</span><span class="p">].(</span><span class="kt">string</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">str1</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Мы также можем декодировать JSON в пользовательские
типы данных. Это дает преимущество добавления
дополнительной безопасности типов в наши программы
и устранения необходимости в определении типрв
при доступе к декодированным данным.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">str</span> <span class="o">:=</span> <span class="s">`{&quot;page&quot;: 1, &quot;fruits&quot;: [&quot;apple&quot;, &quot;peach&quot;]}`</span>
<span class="nx">res</span> <span class="o">:=</span> <span class="nx">response2</span><span class="p">{}</span>
<span class="nx">json</span><span class="p">.</span><span class="nx">Unmarshal</span><span class="p">([]</span><span class="nb">byte</span><span class="p">(</span><span class="nx">str</span><span class="p">),</span> <span class="o">&amp;</span><span class="nx">res</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">res</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">res</span><span class="p">.</span><span class="nx">Fruits</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
</pre></div>
</td>
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<tr>
<td class="docs">
<p>В приведенных выше примерах мы всегда использовали
байты и строки в качестве промежуточных звеньев между
данными и представлением JSON на стандартном выходе.
Мы также можем транслировать JSON-кодировки напрямую
в <code>os.Writer</code>, такие как <code>os.Stdout</code> или даже HTTP-тела
ответа.</p>
</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">enc</span> <span class="o">:=</span> <span class="nx">json</span><span class="p">.</span><span class="nx">NewEncoder</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdout</span><span class="p">)</span>
<span class="nx">d</span> <span class="o">:=</span> <span class="kd">map</span><span class="p">[</span><span class="kt">string</span><span class="p">]</span><span class="kt">int</span><span class="p">{</span><span class="s">&quot;apple&quot;</span><span class="p">:</span> <span class="mi">5</span><span class="p">,</span> <span class="s">&quot;lettuce&quot;</span><span class="p">:</span> <span class="mi">7</span><span class="p">}</span>
<span class="nx">enc</span><span class="p">.</span><span class="nx">Encode</span><span class="p">(</span><span class="nx">d</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
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</table>
<table>
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<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="gp">$</span> go run json.go
<span class="go">true</span>
<span class="go">1</span>
<span class="go">2.34</span>
<span class="go">&quot;gopher&quot;</span>
<span class="go">[&quot;apple&quot;,&quot;peach&quot;,&quot;pear&quot;]</span>
<span class="go">{&quot;apple&quot;:5,&quot;lettuce&quot;:7}</span>
<span class="go">{&quot;Page&quot;:1,&quot;Fruits&quot;:[&quot;apple&quot;,&quot;peach&quot;,&quot;pear&quot;]}</span>
<span class="go">{&quot;page&quot;:1,&quot;fruits&quot;:[&quot;apple&quot;,&quot;peach&quot;,&quot;pear&quot;]}</span>
<span class="go">map[num:6.13 strs:[a b]]</span>
<span class="go">6.13</span>
<span class="go">a</span>
<span class="go">{1 [apple peach]}</span>
<span class="go">apple</span>
<span class="go">{&quot;apple&quot;:5,&quot;lettuce&quot;:7}</span>
</pre></div>
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<td class="docs">
<p>Мы рассмотрели основы JSON в Go, но ознакомьтесь с
публикацией в блоге <a href="http://blog.golang.org/2011/01/json-and-go.html">JSON and Go</a>
и документацией по <a href="http://golang.org/pkg/encoding/json/">пакету JSON</a>.</p>
</td>
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</td>
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</table>
<p class="next">
Следующий пример: <a href="xml">XML</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/json">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
<br/>
переведено Nick S. | <a href="https://github.com/badkaktus/gobyexample">исходники</a>
</p>
</div>
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"encoding/json\"\u000A \"fmt\"\u000A \"os\"\u000A)\u000A');codeLines.push('type response1 struct {\u000A Page int\u000A Fruits []string\u000A}\u000A');codeLines.push('type response2 struct {\u000A Page int `json:\"page\"`\u000A Fruits []string `json:\"fruits\"`\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' bolB, _ := json.Marshal(true)\u000A fmt.Println(string(bolB))\u000A');codeLines.push(' intB, _ := json.Marshal(1)\u000A fmt.Println(string(intB))\u000A');codeLines.push(' fltB, _ := json.Marshal(2.34)\u000A fmt.Println(string(fltB))\u000A');codeLines.push(' strB, _ := json.Marshal(\"gopher\")\u000A fmt.Println(string(strB))\u000A');codeLines.push(' slcD := []string{\"apple\", \"peach\", \"pear\"}\u000A slcB, _ := json.Marshal(slcD)\u000A fmt.Println(string(slcB))\u000A');codeLines.push(' mapD := map[string]int{\"apple\": 5, \"lettuce\": 7}\u000A mapB, _ := json.Marshal(mapD)\u000A fmt.Println(string(mapB))\u000A');codeLines.push(' res1D := &response1{\u000A Page: 1,\u000A Fruits: []string{\"apple\", \"peach\", \"pear\"}}\u000A res1B, _ := json.Marshal(res1D)\u000A fmt.Println(string(res1B))\u000A');codeLines.push(' res2D := &response2{\u000A Page: 1,\u000A Fruits: []string{\"apple\", \"peach\", \"pear\"}}\u000A res2B, _ := json.Marshal(res2D)\u000A fmt.Println(string(res2B))\u000A');codeLines.push(' byt := []byte(`{\"num\":6.13,\"strs\":[\"a\",\"b\"]}`)\u000A');codeLines.push(' var dat map[string]interface{}\u000A');codeLines.push(' if err := json.Unmarshal(byt, &dat); err != nil {\u000A panic(err)\u000A }\u000A fmt.Println(dat)\u000A');codeLines.push(' num := dat[\"num\"].(float64)\u000A fmt.Println(num)\u000A');codeLines.push(' strs := dat[\"strs\"].([]interface{})\u000A str1 := strs[0].(string)\u000A fmt.Println(str1)\u000A');codeLines.push(' str := `{\"page\": 1, \"fruits\": [\"apple\", \"peach\"]}`\u000A res := response2{}\u000A json.Unmarshal([]byte(str), &res)\u000A fmt.Println(res)\u000A fmt.Println(res.Fruits[0])\u000A');codeLines.push(' enc := json.NewEncoder(os.Stdout)\u000A d := map[string]int{\"apple\": 5, \"lettuce\": 7}\u000A enc.Encode(d)\u000A}\u000A');codeLines.push('');codeLines.push('');
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