java中用于解释json的主流工具有org.json、json-lib与gson,本文介绍org.json的应用。

官方文档:

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

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

 

1、主要类

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、构建一个JSON文本的方法

(1)使用JSONObject的构造方法,然后toString。

创建一个JSONObject对象后,再使用put(String, Object)方法添加键值对。

toString()方法将JSONObject对象按照JSON的标准格式进行封装。

(2)使用JSONStringer创建JSON文本。

String myString = new JSONStringer().object()   
.key("name")  
.value("小猪")   
.endObject()  
.toString();
完整程序如下:

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();
	}

}
输出结果如下:

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

结论:

(1)使用JSONObject构造的JSON文本顺序杂乱,使用JSONStringer则按顺序排列。

(2)关于二者之间的比较,android官方文档认为:

 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:

一般情况下使用JSONObject即可,但对于一些嵌套的JSON,某些JSONArray没有key,只有value等特殊情况,则使用JSONStringer.


3、读取JSON文本内容。

使用JSONTokener类的相关方法。

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;
	}
}
输出结果如下:

Jason  20130001   13579246810

事实上,使用JSONObject的构造方法也可直接创建JSONObject对象。

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;
}

总结:单纯使用JSONObject可以解决大部分的JSON处理问题。




GitHub 加速计划 / js / json
19
5
下载
适用于现代 C++ 的 JSON。
最近提交(Master分支:4 个月前 )
f06604fc * :page_facing_up: bump the copyright years Signed-off-by: Niels Lohmann <mail@nlohmann.me> * :page_facing_up: bump the copyright years Signed-off-by: Niels Lohmann <mail@nlohmann.me> * :page_facing_up: bump the copyright years Signed-off-by: Niels Lohmann <niels.lohmann@gmail.com> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me> Signed-off-by: Niels Lohmann <niels.lohmann@gmail.com> 28 天前
d23291ba * add a ci step for Json_Diagnostic_Positions Signed-off-by: Harinath Nampally <harinath922@gmail.com> * Update ci.cmake to address review comments Signed-off-by: Harinath Nampally <harinath922@gmail.com> * address review comment Signed-off-by: Harinath Nampally <harinath922@gmail.com> * fix typo in the comment Signed-off-by: Harinath Nampally <harinath922@gmail.com> * fix typos in ci.cmake Signed-off-by: Harinath Nampally <harinath922@gmail.com> * invoke the new ci step from ubuntu.yml Signed-off-by: Harinath Nampally <harinath922@gmail.com> * issue4561 - use diagnostic positions for exceptions Signed-off-by: Harinath Nampally <harinath922@gmail.com> * fix ci_test_documentation check Signed-off-by: Harinath Nampally <harinath922@gmail.com> * address review comments Signed-off-by: Harinath Nampally <harinath922@gmail.com> * fix ci check failures for unit-diagnostic-postions.cpp Signed-off-by: Harinath Nampally <harinath922@gmail.com> * improvements based on review comments Signed-off-by: Harinath Nampally <harinath922@gmail.com> * fix const correctness string Signed-off-by: Harinath Nampally <harinath922@gmail.com> * further refinements based on reviews Signed-off-by: Harinath Nampally <harinath922@gmail.com> * add one more test case for full coverage Signed-off-by: Harinath Nampally <harinath922@gmail.com> * ci check fix - add const Signed-off-by: Harinath Nampally <harinath922@gmail.com> * add unit tests for json_diagnostic_postions only Signed-off-by: Harinath Nampally <harinath922@gmail.com> * fix ci_test_diagnostics Signed-off-by: Harinath Nampally <harinath922@gmail.com> * fix ci_test_build_documentation check Signed-off-by: Harinath Nampally <harinath922@gmail.com> --------- Signed-off-by: Harinath Nampally <harinath922@gmail.com> 28 天前
Logo

旨在为数千万中国开发者提供一个无缝且高效的云端环境,以支持学习、使用和贡献开源项目。

更多推荐