java生成Json工具之JsonSimple的使用

json-simple是由是Google開發的Java JSON解析框架，基於Apache協議。目前版本爲1.1

項目主頁：https://code.google.com/p/json-simple/#JSON.simple_in_Publications

Java實體類和JSON對象之間的映射以下表：

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

今後表中咱們能夠看出，當解析json對象映射到java實體類時，是從左邊到右邊。從左邊到右邊是Java實體類到json字符。在編碼時默認的JSONArray是繼承了ArrayList實現了List接口，JSONObject是繼承了HashMap實現 了Map接口。jsonsimple默認的只支持表中的幾種類型轉換爲json若是是一個複雜的對象要轉換成Json字符，該類要實現JSONAware接口或者是JSONStreamAware。實現了以上兩個接口後必需要重寫toJSONString()或者writeJSONString()。來輸出json字符。

好了，話很少說，看例子吧！

• Example 1-1 - Encode a JSON object

 // 是java中HashMap的子類
        JSONObject json = new JSONObject(); json.put("name", "張曉天"); json.put("boolean", true); json.put("null", null); json.put("num", 7); json.put("double", 34.5); printJson(json.toJSONString()); // {"num":7,"name":"張曉天","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("張曉天"); list.add(false); list.add(6.9); list.add(7); list.add(null); printJson(list.toJSONString()); // ["foot","張曉天",false,6.9,7,null]

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

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

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

LinkedList list = new LinkedList(); list.add("張曉天"); 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); // ["張曉天",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); // 注意兩個對象的key不能同樣，不然會替換
 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", "第二個值"); 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":"第二個值"},{"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("}"); // 也能夠這樣寫
        /* * 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); } }

若是你使用了maven來建立項目也可在pom中添加如下依賴：

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

</dependency>

總結：jsonsimple對於簡單轉換成json對象，可是對於 比較複雜的對象就不太好了，複雜的對象都要實現JSONAware重寫對應的方法，才能實現指定格式的輸出。