一、JSON介紹
JSON(JavaScript Object Notation),類似於XML,是一種數據交換格式,比如JAVA產生了一個數據想要給JavaScript,則除了利用XML外,還可以利用JSON;
JSON相比XML的優勢是表達起來很簡單;
JSON是AJAX中的X(就是可以取代XML); ------出自JSON創始人;
注意:JSON並不是一個文檔格式,沒有*.json的文檔,一般JSON格式的文檔存在txt中,而XML可以是一個標準;
在線校驗JSON結構的網站:http://www.bejson.com/go.html?u=http://www.bejson.com/jsonview2/
二、JSON數據結構
JSON有兩種數據結構:
(1)Map,也稱爲對象;{....}
(2)Array;[......]
也就是說所有的JSON對象都是要以這些形式表示;
1.Map
簡單的說就是Java中的Map,名稱-值對的形式給出,名稱和值之間用“:”隔開,兩個Map之間用“,”隔開,一般表示形式如下:
{'key1':'value1','key2':'value2'}
以下爲官網的圖:
2.Array
就是普通意義上的數組,一般形式如下:
['arr1','arr2','arr3'];
以下爲官網的圖:
圖中的value可以是:
總結:
(1)JSON的數據結構只有兩種;
(2)可以嵌套表示,比如Array中可以嵌套Object等;
(3)記住:Object是以{}表示,Array是以[ ]表示;
三、JSON與XML互轉示例
前面提到任何的XML都能夠轉換成JSON包;
1.簡單XML
XML格式:
- <person>
- <name>xiazdong</name>
- <age>20</age>
- </person>
<person>
<name>xiazdong</name>
<age>20</age>
</person>
JSON格式:
- {
- "name":"xiazdong",
- "age":20
- }
{
"name":"xiazdong",
"age":20
}
2.複雜XML
XML格式:
- <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>
<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>
JSON格式:
- "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":[
{
"author":
{
"name":"author-1"
},
"book":
{
"title":"book1",
"price":"$11"
}
},
{
"author":
{
"name":"author-2"
},
"book":
{
"title":"book2",
"price":"$22"
}
}
]}
}
注意:XML中的屬性也是通過JSON的Map表示;
四、JSON包
如果我們想要使用JSON包,則可以下載JSON包的源代碼,並將這些代碼添加進Eclipse工程中,即可調用;
如果想要看API文檔,可以參見:http://www.JSON.org/java/index.html
JSON包中最常用的兩個類就是JSONObject和JSONArray,分別表示兩種數據結構;
1.JSONObject代碼實例
- 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);
- }
- }
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);
}
}
2.JSONArray代碼實例
- 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代碼實例
- 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));
- }
- }
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));
}
}
4.JSONStringer代碼示例
JSONStringer可以用來快速構建一個JSON格式的文本,並轉換成String,可以寫入文件;
JSONStringer是JSONWriter的子類;
JSONStringer一般通過object().key().value().key().value().endObject()進行構造;
object()表明開始一個對象,即添加{ ;
endObject()表明結束一個對象,即添加 } ;
array()表明開始一個數組,即添加一個 [ ;
endArray()表明結束一個數組,即添加一個 ] ;
key()表示添加一個key;
value()表示添加一個value;
- 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);
}
}
複雜JSON格式寫入
- 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());
- }
- }
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());
}
}
以上代碼生成了如下JSON格式:
- {"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代碼示例
JSONTokener是用來讀取JSON格式的文件;
JSONObject obj = new JSONObject( new JSONTokener(java.io.Reader));可以從文件中讀取一個JSONObject;
JSONArray obj = new JSONArray( new JSONTokener(java.io.Reader)); 可以從文件中讀取一個JSONArray;
1.txt
- {
- 'name':'xiazdong',
- 'book':['book1','book2']
- }
{
'name':'xiazdong',
'book':['book1','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)); //可以讀取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)); //可以讀取book2
}
}
複雜JSON格式的讀取代碼:
1.txt
- {"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"
}
}
]}
}
}
- 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>//獲取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")); //獲取author-1
}
}
總結:
1在Java中JSON格式的String最好用單引號表示;
2.利用JSONObject+JSONTokener能夠讀取JSON格式文件對象;
3.利用PrintWriter+JSONStringer可以寫入JSON文件;
注:由於原本想要試圖用JSONWriter寫入,但是沒有成功;所以只能利用JSONStringer+PrintWriter寫入;