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Android Json应用
1. Json简介
Json是一种轻量级文本数据交换格式,类似于XML,但比XML更小、更快、更易解析。
Json用于描述数据结构有两个方式
- 名称/值(JSONObject)
- 值的有序列表(JSONArray)
2. 原生Json
(1) JSONObject表示json对象,内部包含了一个Map对象。JSONArray代表数组,内部包含一个List对象。
Json转String,toString()
方法可以生成格式化文本。
private String writeObject() throws JSONException {
JSONObject jsonObject = new JSONObject();
jsonObject.put("aString", "This is json string");
jsonObject.put("aBoolean", true);
jsonObject.put("aInt", 12);
jsonObject.put("aDouble", 1.23);
jsonObject.put("aObject", newPeopleObject("Mike", 24));
JSONArray stringJsonArray = new JSONArray();
stringJsonArray.put("football");
stringJsonArray.put("basketball");
stringJsonArray.put("volleyball");
jsonObject.put("aStringArray", stringJsonArray);
JSONArray objectJsonArray = new JSONArray();
objectJsonArray.put(newPeopleObject("Jack", 26));
objectJsonArray.put(newPeopleObject("Lily", 22));
jsonObject.put("aObjectArray", objectJsonArray);
String json = jsonObject.toString(4);
return json;
}
private JSONObject newPeopleObject(String name, int age) throws JSONException {
JSONObject peopleJsonObject = new JSONObject();
peopleJsonObject.put("name", name);
peopleJsonObject.put("age", age);
return peopleJsonObject;
}
String转Json,通过JSONObject和JSONArray的构造函数赋值。
private GsonData readObject(String json) throws JSONException {
JSONObject jsonObject = new JSONObject(json);
GsonData data = new GsonData();
data.aString = jsonObject.getString("aString");
data.aBoolean = jsonObject.getBoolean("aBoolean");
data.aInt = jsonObject.getInt("aInt");
data.aDouble = jsonObject.getDouble("aDouble");
data.aObject = getPeople(jsonObject.getJSONObject("aObject"));
JSONArray jsonArray = jsonObject.getJSONArray("aStringArray");
data.aStringArray = new String[jsonArray.length()];
for (int index = 0; index < jsonArray.length(); index++) {
data.aStringArray[index] = jsonArray.getString(index);
}
JSONArray objectArray = jsonObject.getJSONArray("aObjectArray");
data.aObjectArray = new People[objectArray.length()];
for (int index = 0; index < objectArray.length(); index++) {
data.aObjectArray[index] = getPeople(objectArray.getJSONObject(index));
}
return data;
}
private People getPeople(JSONObject jsonObject) throws JSONException {
String name = jsonObject.getString("name");
int age = jsonObject.getInt("age");
return new People(name, age);
}
JSONObject和JSONArray提供了很多opt
方法,例如getBoolean
如果返回值为null
的会抛出异常,而opt
方法会提供默认返回值。
public boolean getBoolean(String name) throws JSONException {
Object object = get(name);
Boolean result = JSON.toBoolean(object);
if (result == null) {
throw JSON.typeMismatch(name, object, "boolean");
}
return result;
}
public boolean optBoolean(String name) {
return optBoolean(name, false);
}
public boolean optBoolean(String name, boolean fallback) {
Object object = opt(name);
Boolean result = JSON.toBoolean(object);
return result != null ? result : fallback;
}
(2) JSONTokener用来解析字符串,调用nextValue()
方法获取对象。
public Object nextValue() throws JSONException {
int c = nextCleanInternal();
switch (c) {
case -1:
throw syntaxError("End of input");
case '{':
return readObject();
case '[':
return readArray();
case '\'':
case '"':
return nextString((char) c);
default:
pos--;
return readLiteral();
}
}
例如
JSONTokener tokener = new JSONTokener(json);
JSONObject jsonObject = (JSONObject) tokener.nextValue();
3. Gson
(1) Gson中也提供了JsonObject和JsonArray来操作对象和数组。
Gson转String,Gson的toJson()
方法生成格式化文本。
private String writeObject() {
JsonObject jsonObject = new JsonObject();
jsonObject.addProperty("aString", "This is gson string");
jsonObject.addProperty("aBoolean", true);
jsonObject.addProperty("aInt", 12);
jsonObject.addProperty("aDouble", 1.23);
jsonObject.add("aObject", newPeopleObject("Mike", 24));
JsonArray stringJsonArray = new JsonArray();
stringJsonArray.add("football");
stringJsonArray.add("basketball");
stringJsonArray.add("volleyball");
jsonObject.add("aStringArray", stringJsonArray);
JsonArray objectJsonArray = new JsonArray();
objectJsonArray.add(newPeopleObject("Jack", 26));
objectJsonArray.add(newPeopleObject("Lily", 22));
jsonObject.add("aObjectArray", objectJsonArray);
String json = new Gson()
.toJson(jsonObject);
return json;
}
private JsonObject newPeopleObject(String name, int age) {
JsonObject peopleJsonObject = new JsonObject();
peopleJsonObject.addProperty("name", name);
peopleJsonObject.addProperty("age", age);
return peopleJsonObject;
}
String转Gson,使用JsonParser解析文本获取JsonObject。
private GsonData readObject(String json) {
JsonObject jsonObject = (JsonObject) new JsonParser().parse(json);
GsonData data = new GsonData();
data.aString = jsonObject.get("aString").getAsString();
data.aBoolean = jsonObject.get("aBoolean").getAsBoolean();
data.aInt = jsonObject.get("aInt").getAsInt();
data.aDouble = jsonObject.get("aDouble").getAsDouble();
data.aObject = getPeople(jsonObject.get("aObject").getAsJsonObject());
JsonArray jsonArray = jsonObject.get("aStringArray").getAsJsonArray();
data.aStringArray = new String[jsonArray.size()];
for (int index = 0; index < jsonArray.size(); index++) {
data.aStringArray[index] = jsonArray.get(index).getAsString();
}
JsonArray objectArray = jsonObject.get("aObjectArray").getAsJsonArray();
data.aObjectArray = new People[objectArray.size()];
for (int index = 0; index < objectArray.size(); index++) {
data.aObjectArray[index] = getPeople(objectArray.get(index).getAsJsonObject());
}
return data;
}
private People getPeople(JsonObject jsonObject) {
String name = jsonObject.get("name").getAsString();
int age = jsonObject.get("age").getAsInt();
return new People(name, age);
}
(2) Gson序列化,利用Gson的toJson()
和fromJson()
来实现输入输出。
private String writeJavaBeen() {
GsonData data = new GsonData();
data.aString = "This is gson string";
data.aBoolean = true;
data.aInt = 12;
data.aDouble = 1.23;
data.aObject = new People("Mike", 24);
data.aStringArray = new String[]{"football", "basketball", "volleyball"};
data.aObjectArray = new People[]{ new People("Jack", 26), new People("Lily", 22) };
String json = new Gson()
.toJson(data);
return json;
}
private GsonData readJavaBeen(String json) {
return new Gson().fromJson(json, GsonData.class);
}
如果是数组或者集合,也可以直接调用
new Gson().fromJson(json, String[].class)
new Gson().fromJson(json, new TypeToken<List<String>>(){}.getType())
(3) 过滤属性,详细可参考Android Gson使用详解
- @SerializedName,属性重命名
- @Expose,序列化和反序列化
- @Since和@Until,根据版本过滤,对应
GsonBuilder.setVersion()
- 根据修饰符过滤,对应
GsonBuilder.excludeFieldsWithModifiers()
- 根据策略过滤,对应
GsonBuilder.setExclusionStrategies()
4. FastJson
(1) FastJson中提供了JSONObject和JSONArray来操作对象和数组。
FastJson转String,toJSONString()
方法生成格式化文本。
private String writeObject() {
JSONObject jsonObject = new JSONObject();
jsonObject.put("aString", "This is fastJson string");
jsonObject.put("aBoolean", true);
jsonObject.put("aInt", 12);
jsonObject.put("aDouble", 1.23);
jsonObject.put("aObject", newPeopleObject("Mike", 24));
JSONArray stringJsonArray = new JSONArray();
stringJsonArray.add("football");
stringJsonArray.add("basketball");
stringJsonArray.add("volleyball");
jsonObject.put("aStringArray", stringJsonArray);
JSONArray objectJsonArray = new JSONArray();
objectJsonArray.add(newPeopleObject("Jack", 26));
objectJsonArray.add(newPeopleObject("Lily", 22));
jsonObject.put("aObjectArray", objectJsonArray);
String json = jsonObject.toJSONString();
return json;
}
private JSONObject newPeopleObject(String name, int age) {
JSONObject peopleJsonObject = new JSONObject();
peopleJsonObject.put("name", name);
peopleJsonObject.put("age", age);
return peopleJsonObject;
}
String转FastJson,调用parseObject()
方法获取JSONObject。
private GsonData readObject(String json) {
JSONObject jsonObject = JSONObject.parseObject(json);
GsonData data = new GsonData();
data.aString = jsonObject.getString("aString");
data.aBoolean = jsonObject.getBooleanValue("aBoolean");
data.aInt = jsonObject.getIntValue("aInt");
data.aDouble = jsonObject.getDoubleValue("aDouble");
data.aObject = getPeople(jsonObject.getJSONObject("aObject"));
JSONArray jsonArray = jsonObject.getJSONArray("aStringArray");
data.aStringArray = new String[jsonArray.size()];
for (int index = 0; index < jsonArray.size(); index++) {
data.aStringArray[index] = jsonArray.getString(index);
}
JSONArray objectArray = jsonObject.getJSONArray("aObjectArray");
data.aObjectArray = new People[objectArray.size()];
for (int index = 0; index < objectArray.size(); index++) {
data.aObjectArray[index] = getPeople(objectArray.getJSONObject(index));
}
return data;
}
private People getPeople(JSONObject jsonObject) {
String name = jsonObject.getString("name");
int age = jsonObject.getIntValue("age");
return new People(name, age);
}
(2) FastJson序列化,利用JSON的toJSONString()
和parseObject()
来实现输入输出。
private String writeJavaBeen() {
GsonData data = new GsonData();
data.aString = "This is gson string";
data.aBoolean = true;
data.aInt = 12;
data.aDouble = 1.23;
data.aObject = new People("Mike", 24);
data.aStringArray = new String[]{"football", "basketball", "volleyball"};
data.aObjectArray = new People[]{ new People("Jack", 26), new People("Lily", 22) };
String json = JSON.toJSONString(data);
return json;
}
private GsonData readJavaBeen(String json) {
return JSON.parseObject(json, GsonData.class);
}
如果是数组或者集合,也可以直接调用
JSON.parseObject(json, String[].class)
JSON.parseObject(json, new TypeReference<List<String>>(){}.getType())