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JSON for java入门总结 .

2011-12-18 15:10 162 查看

一、JSON介绍

JSON(JavaScript Object Notation),类似于XML,是一种数据交换格式,比如JAVA产生了一个数据想要给JavaScript,则除了利用XML外,还可以利用JSON;

JSON相比XML的优势是表达起来很简单;

官网:http://www.json.org/

JSON是AJAX中的X(就是可以取代XML); ------出自JSON创始人;

注意:JSON并不是一个文档格式,没有*.json的文档,一般JSON格式的文档存在txt中,而XML可以是一个标准;

二、JSON数据结构

JSON有两种数据结构:

(1)Map,也称为对象;{....}

(2)Array;[......]

也就是说所有的JSON对象都是要以这些形式表示;

1.Map

简单的说就是Java中的Map,名称-值对的形式给出,名称和值之间用“:”隔开,两个Map之间用“,”隔开,一般表示形式如下:

{'key1':'value1','key2':'value2'}

以下为官网的图:



2.Array

就是普通意义上的数组,一般形式如下:

['arr1','arr2','arr3'];

以下为官网的图:



图中的value可以是:



总结:

(1)JSON的数据结构只有两种;

(2)可以嵌套表示,比如Array中可以嵌套Object等;

(3)记住:Object是以{}表示,Array是以[ ]表示;

三、JSON与XML互转示例

前面提到任何的XML都能够转换成JSON包;

1.简单XML

XML格式:

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<person>
<name>xiazdong</name>
<age>20</age>
</person>

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{
"name":"xiazdong",
"age":20
}

{
"name":"xiazdong",
"age":20
}


2.复杂XML

XML格式:

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<section>

<title>BOOK</title>

<signing>

<author name="author-1"/>

<book title="book1" price="$11"/>

</signing>

<signing>

<author name="author-2"/>

<book title="book2" price="$22"/>

</signing>

</section>

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"section":{
"title":"BOOK",
"signing":[
{
<span style="white-space:pre">    </span>   "author":

{
"name":"author-1"
},
"book":
{
"title":"book1",
"price":"$11"
}
},
{
"author":
{
"name":"author-2"
},
"book":
{
"title":"book2",
"price":"$22"
}
}
<span style="white-space:pre">    </span>   ]}

}

"section":{
"title":"BOOK",
"signing":[
{
<span style="white-space:pre">	</span>	"author":
{
"name":"author-1"
},
"book":
{
"title":"book1",
"price":"$11"
}
},
{
"author":
{
"name":"author-2"
},
"book":
{
"title":"book2",
"price":"$22"
}
}
<span style="white-space:pre">	</span>	]}
}


注意:XML中的属性也是通过JSON的Map表示;

四、JSON包

如果我们想要使用JSON包,则可以下载JSON包的源代码,并将这些代码添加进Eclipse工程中,即可调用;

如果想要看API文档,可以参见:http://www.JSON.org/java/index.html

JSON包中最常用的两个类就是JSONObject和JSONArray,分别表示两种数据结构;

1.JSONObject代码实例

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package com.xiazdong.json;

import weibo4j.org.json.JSONArray;

import weibo4j.org.json.JSONObject;

public class Test {

public static void main(String[] args) throws Exception{

JSONObject jsonobj = new JSONObject("{'name':'xiazdong','age':20}");

String name = jsonobj.getString("name");

int age = jsonobj.getInt("age");

System.out.println(name+":"+age);

}
}

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package com.xiazdong.json;

import weibo4j.org.json.JSONArray;

import weibo4j.org.json.JSONObject;

public class Test {

public static void main(String[] args) throws Exception{

JSONArray jsonarray = new JSONArray("[{'name':'xiazdong','age':20},{'name':'xzdong','age':15}]");

for(int i=0;i<jsonarray.length();i++){

String name = jsonarray.getJSONObject(i).getString("name");

int age = jsonarray.getJSONObject(i).getInt("age");

System.out.println("name="+name);

System.out.println("age="+age);

}

}
}

package com.xiazdong.json;

import weibo4j.org.json.JSONArray;
import weibo4j.org.json.JSONObject;

public class Test {

public static void main(String[] args) throws Exception{

JSONArray jsonarray = new JSONArray("[{'name':'xiazdong','age':20},{'name':'xzdong','age':15}]");
for(int i=0;i<jsonarray.length();i++){
String name = jsonarray.getJSONObject(i).getString("name");
int age = jsonarray.getJSONObject(i).getInt("age");
System.out.println("name="+name);
System.out.println("age="+age);
}

}
}


3.嵌套JSONObject和JSONArray代码实例

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package com.xiazdong.json;

import weibo4j.org.json.JSONArray;

import weibo4j.org.json.JSONObject;

public class Test {

public static void main(String[] args) throws Exception{

String str = "{'name':'xiazdong','age':20,'book':['book1','book2']";

JSONObject obj = new JSONObject(str);

System.out.println(obj.getJSONArray("book").getString(0));

}
}

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package com.xiazdong.json;

import weibo4j.org.json.JSONStringer;

public class JsonStringerDemo {

public static void main(String[] args) throws Exception{

JSONStringer stringer = new JSONStringer();

String str = stringer.object().key("name").value("xiazdong").key("age").value(20).endObject().toString();

System.out.println(str);
}

}

package com.xiazdong.json;

import weibo4j.org.json.JSONStringer;

public class JsonStringerDemo {

public static void main(String[] args) throws Exception{
JSONStringer stringer = new JSONStringer();
String str = stringer.object().key("name").value("xiazdong").key("age").value(20).endObject().toString();
System.out.println(str);
}

}


复杂JSON格式写入

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package com.xiazdong.json;

import java.io.File;

import java.io.FileReader;

import weibo4j.org.json.JSONArray;

import weibo4j.org.json.JSONObject;

import weibo4j.org.json.JSONStringer;

import weibo4j.org.json.JSONTokener;

public class JsonStringerDemo {

public static void main(String[] args) throws Exception{

JSONStringer js = new JSONStringer();

JSONObject obj2 = new JSONObject();

JSONObject obj3 = new JSONObject();

JSONObject obj4 = new JSONObject();

obj4.put("title", "book1").put("price", "$11");

obj3.put("book", obj4);

obj3.put("author", new JSONObject().put("name", "author-1"));

JSONObject obj5 = new JSONObject();

JSONObject obj6 = new JSONObject();

obj6.put("title", "book2").put("price", "$22");

obj5.put("book", obj6);

obj5.put("author", new JSONObject().put("name", "author-2"));

JSONArray obj7 = new JSONArray();

obj7.put(obj3).put(obj5);

obj2.put("title","BOOK");

obj2.put("signing", obj7);

js.object().key("session").value(obj2).endObject();

System.out.println(js.toString());

PrintWriter out = new PrintWriter(new FileOutputStream(1.txt));

out.println(js.toString());

}

}

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{"section":{

"title":"BOOK",

"signing":[

{
"author":

{
"name":"author-1"

},
"book":

{
"title":"book1",

"price":"$11"

}
},
{
"author":

{
"name":"author-2"

},
"book":
{
"title":"book2",

"price":"$22"

}
}
]}
}
}

{"section":{
"title":"BOOK",
"signing":[
{
"author":
{
"name":"author-1"
},
"book":
{
"title":"book1",
"price":"$11"
}
},
{
"author":
{
"name":"author-2"
},
"book":
{
"title":"book2",
"price":"$22"
}
}
]}
}
}




5.JSONTokener代码示例

JSONTokener是用来读取JSON格式的文件;

JSONObject obj = new JSONObject( new JSONTokener(java.io.Reader));可以从文件中读取一个JSONObject;

JSONArray obj = new JSONArray( new JSONTokener(java.io.Reader)); 可以从文件中读取一个JSONArray;

1.txt

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{
'name':'xiazdong',

'book':['book1','book2']

}

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package com.xiazdong.json;

import java.io.File;

import java.io.FileReader;

import weibo4j.org.json.JSONObject;

import weibo4j.org.json.JSONTokener;

public class JsonStringerDemo {

public static void main(String[] args) throws Exception{

JSONObject obj = new JSONObject(new JSONTokener(new FileReader(new File("1.txt"))));

System.out.println(obj.getJSONArray("book").getString(1)); //可以读取book2

}

}

package com.xiazdong.json;

import java.io.File;
import java.io.FileReader;

import weibo4j.org.json.JSONObject;
import weibo4j.org.json.JSONTokener;

public class JsonStringerDemo {

public static void main(String[] args) throws Exception{
JSONObject obj = new JSONObject(new JSONTokener(new FileReader(new File("1.txt"))));
System.out.println(obj.getJSONArray("book").getString(1)); //可以读取book2
}

}


复杂JSON格式的读取代码:

1.txt

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{"section":{

"title":"BOOK",

"signing":[

{
"author":

{
"name":"author-1"

},
"book":

{
"title":"book1",

"price":"$11"

}
},
{
"author":

{
"name":"author-2"

},
"book":
{
"title":"book2",

"price":"$22"

}
}
]}
}
}

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package com.xiazdong.json;

import java.io.File;

import java.io.FileReader;

import weibo4j.org.json.JSONObject;

import weibo4j.org.json.JSONTokener;

public class JsonStringerDemo {

public static void main(String[] args) throws Exception{

JSONObject obj = new JSONObject(new JSONTokener(new FileReader(new File("1.txt"))));

System.out.println(obj.getJSONObject("section").getJSONArray("signing").getJSONObject(0).getJSONObject("author").getString("name")); <span style="white-space:pre">       </span>//获取author-1

}

}

package com.xiazdong.json;

import java.io.File;
import java.io.FileReader;

import weibo4j.org.json.JSONObject;
import weibo4j.org.json.JSONTokener;

public class JsonStringerDemo {

public static void main(String[] args) throws Exception{
JSONObject obj = new JSONObject(new JSONTokener(new FileReader(new File("1.txt"))));
System.out.println(obj.getJSONObject("section").getJSONArray("signing").getJSONObject(0).getJSONObject("author").getString("name")); <span style="white-space:pre">		</span>//获取author-1
}

}


总结:

1在Java中JSON格式的String最好用单引号表示;

2.利用JSONObject+JSONTokener能够读取JSON格式文件对象;

3.利用PrintWriter+JSONStringer可以写入JSON文件;

注:由于原本想要试图用JSONWriter写入,但是没有成功;所以只能利用JSONStringer+PrintWriter写入;
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