java生成Json工具之JsonSimple的使用

json-simple是由是Google开发的Java JSON解析框架，基于Apache协议。目前版本为1.1

项目主页：https://code.google.com/p/json-simple/

Java实体类和JSON对象之间的映射如下表：

JSON	Java
string	java.lang.String
number	java.lang.Number
true\|false	java.lang.Boolean
null	null
array	java.util.List
object	java.util.Map

从此表中我们可以看出，当解析json对象映射到java实体类时，是从左边到右边。从左边到右边是Java实体类到json字符。在编码时默认的JSONArray是继承了ArrayList实现了List接口，JSONObject是继承了HashMap实现了Map接口。jsonsimple默认的只支持表中的几种类型转换为json如果是一个复杂的对象要转换成Json字符，该类要实现JSONAware接口或者是JSONStreamAware。实现了以上两个接口后必须要重写toJSONString()或者writeJSONString()。来输出json字符。

好了，话不多说，看例子吧！

Example 1-1 – Encode a JSON object

       // 是java中HashMap的子类
        JSONObject json = new JSONObject();
        json.put("name", "张晓天");
        json.put("boolean", true);
        json.put("null", null);
        json.put("num", 7);
        json.put("double", 34.5);
        printJson(json.toJSONString());
        // {"num":7,"name":"张晓天","boolean":true,"double":34.5,"null":null}

Example 1-2 – Encode a JSON object – Streaming

JSONObject obj = new JSONObject();
        obj.put("name", "foo");
        obj.put("num", new Integer(100));
        obj.put("balance", new Double(1000.21));
        obj.put("is_vip", new Boolean(true));
        obj.put("nickname", null);
        StringWriter out = new StringWriter();
        try {
            obj.writeJSONString(out);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        String jsonText = out.toString();
        printJson(jsonText);
        // {"balance":1000.21,"num":100,"nickname":null,"is_vip":true,"name":"foo"}

Example 2-1 – Encode a JSON array

      JSONArray list = new JSONArray();
        list.add("foot");
        list.add("张晓天");
        list.add(false);
        list.add(6.9);
        list.add(7);
        list.add(null);
        printJson(list.toJSONString());
        // ["foot","张晓天",false,6.9,7,null]

Example 2-2 – Encode a JSON array – Using List

      List list = new LinkedList<>();
        list.add("foot");
        list.add("张晓天");
        list.add(false);
        list.add(6.9);
        list.add(7);
        list.add(null);
        String jsonText = JSONValue.toJSONString(list);
        printJson(jsonText);
        // ["foot","张晓天",false,6.9,7,null]

Example 2-3- Encode a JSON array – Using List and streaming

       LinkedList list = new LinkedList();
        list.add("张晓天");
        list.add(100);
        list.add(1000.21);
        list.add(true);
        list.add(null);
        StringWriter out = new StringWriter();
        try {
            JSONValue.writeJSONString(list, out);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        String jsonText = out.toString();
        printJson(jsonText);
        // ["张晓天",100,1000.21,true,null]

Example 3 – Merge two JSON objects

       JSONObject json1 = new JSONObject();
        json1.put("name", "json1");
        json1.put("age", 3);
        json1.put("balance", 3.8);        JSONObject json2 = new JSONObject();
        json2.put("is_vip", "是");
        json2.put("nickname", null);
        json2.put("num", 8.9);
        json2.putAll(json1); // 注意两个对象的key不能一样，否则会替换
        printJson(json2.toJSONString());
        // {"balance":3.8,"num":8.9,"nickname":null,"is_vip":"是","name":"json1","age":3}

Example 4 – Merge two JSON arrays

    JSONArray list1 = new JSONArray();
        list1.add("foo");
        list1.add(new Integer(100));
        list1.add(new Double(1000.21));        JSONArray list2 = new JSONArray();
        list2.add(new Boolean(true));
        list2.add(null);        JSONObject obj = new JSONObject();
        obj.put("name", "foo");
        obj.put("num", new Integer(100));
        obj.put("balance", new Double(1000.21));
        obj.put("is_vip", new Boolean(true));
        obj.put("nickname", null);        obj.put("list1", list1);
        obj.put("list2", list2);
        printJson(obj.toJSONString());        // {"balance":1000.21,"list2":[true,null],"num":100,"list1":["foo",100,1000.21],"nickname":null,"is_vip":true,"name":"foo"}

Example 5-1 – Combination of JSON primitives, Map and List

        Map m1 = new LinkedHashMap();
        Map m2 = new HashMap();
        List l1 = new LinkedList();        m1.put("one", "第一值");
        m1.put("two", "第二个值");
        m2.put("k1", "m2-k1");
        m2.put("k2", "m2-k2");        l1.add(m1);
        l1.add(m2);
        String json = JSONValue.toJSONString(l1);
        printJson(json);
        // [{"one":"第一值","two":"第二个值"},{"k1":"m2-k1","k2":"m2-k2"}]

Example 5-2 – Combination of JSON primitives, JSONObject, Map and List, and streaming

        StringWriter out = new StringWriter();
        JSONObject obj = new JSONObject();
        LinkedHashMap m1 = new LinkedHashMap();
        LinkedList l1 = new LinkedList();
        obj.put("k1", "v1");
        obj.put("k2", m1);
        obj.put("k3", l1);
        m1.put("mk1", "mv1");
        l1.add("lv1");
        l1.add("lv2");
        m1.put("mk2", l1);
        try {
            obj.writeJSONString(out);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("jsonString:");
        System.out.println(out.toString());
        String jsonString = obj.toJSONString();
        System.out.println(jsonString);

Example 6 – Customize JSON outputs

JSONArray users = new JSONArray();
        users.add(new User(123, "zxd", "zxd"));
        users.add(new User(124, "ksks", "ksk"));
        users.add(new User(125, "\"foo2\"", "secret2"));
        printJson(users.toJSONString());
        // [{userName:"zxd",ID:123},{userName:"ksks",ID:124},{userName:"\"foo2\"",ID:125}]

JSONArray users = new JSONArray();
        users.add(new User(123, "foo1", "secret1"));
        users.add(new User(124, "foo2", "secret2"));
        users.add(new User(125, "\"foo2\"", "secret2"));
        StringWriter out = new StringWriter();
        try {
            users.writeJSONString(out);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        printJson(out.toString());        //[{userName:"foo1",ID:123},{userName:"foo2",ID:124},{userName:"\"foo2\"",ID:125}]

class User implements JSONAware {
    private int id;
    private String name;
    private String password;    public User(int id, String name, String password) {
        this.id = id;
        this.name = name;
        this.password = password;
    }    public String toJSONString() {
        StringBuffer sb = new StringBuffer();        sb.append("{");        sb.append(JSONObject.escape("userName"));
        sb.append(":");
        sb.append("\"" + JSONObject.escape(name) + "\"");        sb.append(",");        sb.append(JSONObject.escape("ID"));
        sb.append(":");
        sb.append(id);        sb.append("}");
        // 也可以这样写
        /*
         * JSONObject obj = new JSONObject(); obj.put("userName", name);
         * obj.put("ID", new Integer(id)); return obj.toString();
         */
        return sb.toString();    }    public void writeJSONString(Writer out) throws IOException {
        LinkedHashMap obj = new LinkedHashMap();
        obj.put("userName", name);
        obj.put("ID", new Integer(id));
        JSONValue.writeJSONString(obj, out);
    }
}

如果你使用了maven来创建项目也可在pom中添加以下依赖：

<dependency>
<groupId>com.googlecode.json-simple</groupId>
<artifactId>json-simple</artifactId>
<version>1.1.1</version></dependency>

总结：jsonsimple对于简单转换成json对象，但是对于比较复杂的对象就不太好了，复杂的对象都要实现JSONAware重写对应的方法，才能实现指定格式的输出。

Java实体类和JSON对象之间的映射如下表：

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