JSON入門之二：org.json的基本使用方法

java中用於解釋json的主流工具有org.json、json-lib與gson。本文介紹org.json的應用。

官方文檔：

http://www.json.org/java/

http://developer.android.com/reference/org/json/package-summary.html

 

1、主要類

Classes

---

JSONArray	A dense indexed sequence of values.
JSONObject	A modifiable set of name/value mappings.
JSONStringer	Implements toString() and toString().
JSONTokener	Parses a JSON (RFC 4627) encoded string into the corresponding object.

Exceptions

---

JSONException

Thrown to indicate a problem with the JSON API.

 

2、構建一個JSON文本的方法

（1）使用JSONObject的構造方法。然后toString。

創建一個JSONObject對象后。再使用put(String, Object)方法加入鍵值對。

toString()方法將JSONObject對象依照JSON的標准格式進行封裝。

（2）使用JSONStringer創建JSON文本。

String myString = new JSONStringer().object()   
.key("name")  
.value("小豬")   
.endObject()  
.toString();

完整程序例如以下：

package com.ljh.jsondemo;

import org.json.JSONException;
import org.json.JSONObject;
import org.json.JSONStringer;
import org.junit.Test;

public class JSONObjectTest {

	@Test
	public void test() {
		System.out.println(prepareJSONObject());
		System.out.println(prepareJSONObject2());
	}
	
	private static String prepareJSONObject(){
		JSONObject studentJSONObject = new JSONObject();
		try {
			studentJSONObject.put("name", "Jason");
			studentJSONObject.put("id", 20130001);
			studentJSONObject.put("phone", "13579246810");
		} catch (JSONException e) {
			e.printStackTrace();
		}
		
		return studentJSONObject.toString();
	}
	
	private static String prepareJSONObject2(){
		JSONStringer jsonStringer = new JSONStringer();
		try {
			jsonStringer.object();
			jsonStringer.key("name");
			jsonStringer.value("Jason");
			jsonStringer.key("id");
			jsonStringer.value(20130001);
			jsonStringer.key("phone");
			jsonStringer.value("13579246810");
			jsonStringer.endObject();
		} catch (JSONException e) {
			e.printStackTrace();
		}
		return jsonStringer.toString();
	}

}

輸出結果例如以下：

{"id":20130001,"phone":"13579246810","name":"Jason"}
{"name":"Jason","id":20130001,"phone":"13579246810"}

結論：

（1）使用JSONObject構造的JSON文本順序雜亂，使用JSONStringer則按順序排列。

（2）關於二者之間的比較。android官方文檔覺得：

 Most application developers should use those methods directly and disregard this API. For example:

 JSONObject object = ...
 String json = object.toString();

Stringers only encode well-formed JSON strings. In particular:

• The stringer must have exactly one top-level array or object.
• Lexical scopes must be balanced: every call to array() must have a matching call to endArray() and every call to object() must have a matching call to endObject().
• Arrays may not contain keys (property names).
• Objects must alternate keys (property names) and values.
• Values are inserted with either literal value calls, or by nesting arrays or objects.

Calls that would result in a malformed JSON string will fail with a  JSONException .

This class provides no facility for pretty-printing (ie. indenting) output. To encode indented output, use toString(int) or toString(int).

Some implementations of the API support at most 20 levels of nesting. Attempts to create more than 20 levels of nesting may fail with a JSONException.

Each stringer may be used to encode a single top level value. Instances of this class are not thread safe. Although this class is nonfinal, it was not designed for inheritance and should not be subclassed. In particular, self-use by overrideable methods is not specified. See Effective Java Item 17, "Design and Document or inheritance or else prohibit it" for further information.

即：

普通情況下使用JSONObject就可以，但對於一些嵌套的JSON，某些JSONArray沒有key,僅僅有value等特殊情況。則使用JSONStringer.

3、讀取JSON文本內容。

使用JSONTokener類的相關方法。

package com.ljh.jsondemo;

import org.json.JSONException;
import org.json.JSONObject;
import org.json.JSONTokener;
import org.junit.Test;

public class JSONTokenerTEst {

	@Test
	public void test() {
		System.out.println(getJSONContent());
	}
	
	private static String JSONText = "{\"id\":20130001,\"phone\":\"13579246810\",\"name\":\"Jason\"}";
	
	private static String getJSONContent(){
		JSONTokener jsonTokener = new JSONTokener(JSONText); 
		JSONObject studentJSONObject;
		String name = null;
		int id = 0;
		String phone = null;
		try {
			studentJSONObject = (JSONObject) jsonTokener.nextValue();
			name = studentJSONObject.getString("name");
			id = studentJSONObject.getInt("id");
			phone = studentJSONObject.getString("phone");
			
		} catch (JSONException e) {
			e.printStackTrace();
		}
		return name + "  " + id + "   " + phone;
	}
}

輸出結果例如以下：

Jason  20130001   13579246810

其實，使用JSONObject的構造方法也可直接創建JSONObject對象。

private static String getJSONContent2(){
	String name = null;
	int id = 0;
	String phone = null;
	try {
		JSONObject studentJSONObject = new JSONObject(JSONText); 
		name = studentJSONObject.getString("name");
		id = studentJSONObject.getInt("id");
		phone = studentJSONObject.getString("phone");
		
	} catch (JSONException e) {
		e.printStackTrace();
	}
	return name + "  " + id + "   " + phone;
}

總結：單純使用JSONObject能夠解決大部分的JSON處理問題。