org.json使用指南

@(博客文章)[json]

常见的json解释库有org.json,gson,json-lib,json-simple等，这里介绍了org.json的用法。

（一）概述

org.json库非常简单，只有4个类一个异常。单纯使用JSONObject可以解决大部分的JSON处理问题。

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. 
JSONException   Thrown to indicate a problem with the JSON API.

（二）生成Json文本

1、使用JSONObject

public static String generateJsonString(){
    JSONObject studentJSONObject = new JSONObject();
    try {
        studentJSONObject.put("id",5);
        studentJSONObject.put("name","Jason");
        studentJSONObject.put("phone","13579246810");
    } catch (JSONException e) {
        e.printStackTrace();
    }
    return studentJSONObject.toString();

}

2、使用JSONString

private static String generateJsonString2(){  
    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();
}

3、小结

（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.

（三）读取Json文本

1、使用JSONObject

public static String getJSONContent(){  
    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;  
}

2、使用JSONTokener

public static String getJSONContent2(){  
    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;  
}