Json数据的解析

   一、概述

    JSON(JavaScript Object Notation) 是一种轻量级的数据交换格式。它基于ECMAScript的一个子集。 JSON采用完全独立于语言的文本格式， 易于人阅读和编写，同时也易于机器解析和生成(一般用于提升网络传输速率)。

二、语法规则

  （1）、JSON 语法是 JavaScript 对象表示语法的子集。

• 数据在键值对中
• 数据由逗号分隔
• 花括号保存对象
• 方括号保存数组

例如：
JSON 数据的书写格式是：名称/值对
名称/值对组合中的名称写在前面（在双引号中），值对写在后面(同样在双引号中)，中间用冒号隔开：

"firstName":"John"

(2)、JSON 值可以是：

• 数字（整数或浮点数）
• 字符串（在双引号中）
• 逻辑值（true 或 false）
• 数组（在方括号中）
• 对象（在花括号中）
• null

三、JSON的两种结构

JSON有两种表示结构，对象和数组。
（1）、对象结构以”{”大括号开始，以”}”大括号结束。中间部分由0或多个以”，”分隔的”key(关键字)/value(值)”对构成，关键字和值之间以”：”分隔，语法结构如代码。

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    {        key1:value1,        key2:value2,        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

（2）、数组结构以”[”开始，”]”结束。中间由0或多个以”，”分隔的值列表组成，语法结构如代码。

<code class="hljs ini has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    <span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 102, 102);">[        {            key1:value1,            key2:value2         },        {             key3:value3,             key4:value4           }    ]</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li><li style="box-sizing: border-box; padding: 0px 5px;"></li><li style="box-sizing: border-box; padding: 0px 5px;"></li><li style="box-sizing: border-box; padding: 0px 5px;"></li><li style="box-sizing: border-box; padding: 0px 5px;"></li><li style="box-sizing: border-box; padding: 0px 5px;"></li><li style="box-sizing: border-box; padding: 0px 5px;"></li><li style="box-sizing: border-box; padding: 0px 5px;"></li><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

下面我们开始学习Json数据的解析。首先我们下载gson.jar包，然后导入Android Studio中，注意，要在module的gradle文件中添加：

<code class="hljs livecodeserver has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    compile <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">files</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'libs/gson-2.3.0.jar'</span>)</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

我们需要明白三个类：Gson、JsonObject、JsonArray。
（1）、Gson类：
Gson是一个工具类，需要使用gson.jar包，使用很简单，用于将Json字符串的转换。主要的两个方法：

• toJson()
• fromJson()

例如：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> String <span class="hljs-title" style="box-sizing: border-box;">ObjectToJson</span>(Object <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">object</span>){        Gson gson = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Gson();        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> gson.toJson(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">object</span>);    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

通过这两个方法，可以将我们的对象实体转换成键值对的json字符串。
（2）、JsonObject类：
json对象，就是一个键对应一个值，使用的是大括号{ }，如：{key:value}

<code class="hljs json has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">{"<span class="hljs-attribute" style="box-sizing: border-box;">author</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"何红辉、关爱民"</span></span>,"<span class="hljs-attribute" style="box-sizing: border-box;">name</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Android源码设计模式解析与实战"</span></span>,"<span class="hljs-attribute" style="box-sizing: border-box;">price</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"79.0"</span></span>}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

常用方法：
（1）、构造方法：

• public JSONObject(String json) throws JSONException：将json字符串转换成JSONObject对象
• public JSONObject(Map copyFrom)：由一个Map集合内容构成一个JSONObject对象。

（2）普通方法：

• public int length()：返回JSONObject中有多少对键值对
• JSONObject put(String name, **) throws JSONException：向JSONObject中填充键值对。
• get()：用于获取里面的键值对值
• JSONArray getJSONArray(String name)：获取JSONObject中key对应的JSONArray对象。

例如：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    JSONObject jsonObject = new JSONObject()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonObject<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"author"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"何红辉、关爱民"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonObject<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Android源码设计模式解析与实战"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonObject<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"price"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"79.0"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

（3）、JsonArray类：
JsonObject数组，使用中括号[ ]包含。

<code class="hljs json has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    [{"<span class="hljs-attribute" style="box-sizing: border-box;">author</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"何红辉、关爱民"</span></span>,"<span class="hljs-attribute" style="box-sizing: border-box;">price</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"79.0"</span></span>,"<span class="hljs-attribute" style="box-sizing: border-box;">name</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Android源码设计模式解析与实战"</span></span>}]</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

常用方法：
（1）、构造方法：

• JSONArray()：无参构造方法，生成一个对象
• public JSONArray(Collection copyFrom)：从Collection集合生成对象
• public JSONArray(String json) throws JSONException：从json字符串生成对象
• put(Object)：向JSONArray中添加值
• put(int ,object)：在jsonarray指定下标位置添加值。
• get(int)：根绝指定下标获取值

例如：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    JSONArray jsonArray = new JSONArray()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(jsonObject)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    Log<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.d</span>(TAG,jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.toString</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

实例，大家可以自己写几个试试，我们现在写个小demo，随便看看

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    JSONObject jsonObject = new JSONObject()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonObject<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"author"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"何红辉、关爱民"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonObject<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Android源码设计模式解析与实战"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonObject<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"price"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"79.0"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    JSONArray jsonArray = new JSONArray()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(jsonObject)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1314</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(true)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    Log<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.d</span>(TAG,jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.toString</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

输入结果：

<code class="hljs json has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    [{"<span class="hljs-attribute" style="box-sizing: border-box;">author</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"何红辉、关爱民"</span></span>,"<span class="hljs-attribute" style="box-sizing: border-box;">price</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"79.0"</span></span>,"<span class="hljs-attribute" style="box-sizing: border-box;">name</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Android源码设计模式解析与实战"</span></span>},<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1314</span>,<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>]</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

我们在看下面：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    JSONObject jsonObject = new JSONObject()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonObject<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"author"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"何红辉、关爱民"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonObject<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Android源码设计模式解析与实战"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonObject<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"price"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"79.0"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    JSONArray jsonArray = new JSONArray()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(jsonObject)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1314</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(true)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.put</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"在1的位置添加"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>    Log<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.d</span>(TAG,jsonArray<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.toString</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"></li></ul>

看看输出结果：

<code class="hljs json has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    [{"<span class="hljs-attribute" style="box-sizing: border-box;">author</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"何红辉、关爱民"</span></span>,"<span class="hljs-attribute" style="box-sizing: border-box;">price</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"79.0"</span></span>,"<span class="hljs-attribute" style="box-sizing: border-box;">name</span>":<span class="hljs-value" style="box-sizing: border-box;"><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Android源码设计模式解析与实战"</span></span>},<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"在1的位置添加"</span>,<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>]</code>