學習筆記:Android裡JSON解析的幾種方法
一、解析方法:
Android解析json有很多種方法,下面介紹三種方法:Android自帶的org.json解析、Gson解析和Jackson解析。
優缺點對比:
Android自帶的方法有點像xml的dom解析,遍歷之後根據需要的key值去取資料,操作比較複雜,而且速度比較慢;Gson方法只需要建立一個對應json的javaBean類,就可以通過簡單的操作解析出資料,而且速度比較快,還可以按需去取資料;Jackson方法是三種方法裡面最快的一種,在資料量的的情況優勢尤為明顯,也是像Gson一樣要建立對應的javaBean,但是缺點是一定要讀取所有key,如果要按需解析的話可以拆分json來讀取,操作比較麻煩。
PS:從伺服器或從本地讀取的json資料有可能含有BOM頭,讀入的話會導致json資料解析失敗,所以需要去除BOM頭,因為java在讀取Unicode檔案的時候,會統一把BOM變成“\uFEFF”,所以可以:
if(line.startsWith("\uFEFF")){
line = line.replace("\uFEFF", "");//去除BOM頭
}
下面請看我學習json解析中運用到3個方法的例子(以下例子使用Android Studio編譯)
二、Android Studio自帶org.json解析:
1.解析一個json資料:
{
"student":[
{"id":1,"name":"小明","sex":"男","age":18,"height":175},
{"id":2,"name":"小紅","sex":"女","age":19,"height":165},
{"id":3,"name":"小強","sex":"男","age":20,"height":185}
],
"cat":"it"
}
2.讀入本地assets資料夾裡面的student.json並解析
package scut.learngson;
import android.os.Bundle;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
EntityStudent student = new EntityStudent();
try {
InputStreamReader isr = new InputStreamReader(this.getClass().getClassLoader().getResourceAsStream("assets/" + "student.json"));
//從assets獲取json檔案,和eclipse裡面的方法不同,我搞了好久才發現
BufferedReader bfr = new BufferedReader(isr);//位元組流轉字元流
String line ;
StringBuilder stringBuilder = new StringBuilder();
while ((line = bfr.readLine())!=null){
stringBuilder.append(line);
}//將JSON資料轉化為字串
JSONObject root = new JSONObject(stringBuilder.toString());
System.out.println("root:"+root.getString("cat"));//根據鍵名獲取鍵值資訊
JSONArray array = root.getJSONArray("student");
for (int i = 0;i < array.length();i++)
{
JSONObject stud = array.getJSONObject(i);
System.out.println("------------------");
System.out.print("id="+stud.getInt("id")+ ","));
System.out.print("name="+stud.getString("name")+ ","));
System.out.print("sex="+stud.getString("sex")+ ","));
System.out.print("age="+stud.getInt("age")+ ","));
System.out.println("height="+stud.getInt("height")+ ","));
bfr.close();
isr.close();
is.close();//依次關閉流
}
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
}
}
}
輸出
System.out: ------------------
System.out: id=1,name=小明,sex=男,age=18,height=175,
System.out: id=2,name=小紅,sex=女,age=19,height=165,
System.out: id=3,name=小強,sex=男,age=20,height=185,
三、Gson解析
1.Gson簡單解析
一個JavaBean(json用gson轉化的時候要有一個實體類對應):
PS:用Gson解析的話,JavaBean裡面的屬性不一定要全部和json資料裡面的所有key對應,可以按需取資料。
package scut.learngson;
public class EntityStudent {
private int id;
private String name;
private String sex;
private int age;
private int height;
public void setId(int id){
this.id = id;
}
public void setName(String name){
this.name = name;
}
public void setSex(String sex){
this.sex = sex;
}
public void setAge(int age){
this.age = age;
}
public void setHeight(int height){
this.height = height;
}
public int getId(){
return id;
}
public String getName(){
return name;
}
public String getSex(){
return sex;
}
public int getAge(){
return age;
}
public int getHeight(){
return height;
}
public void show(){
System.out.print("id=" + id + ",");
System.out.print("name=" + name+",");
System.out.print("sex=" + sex+",");
System.out.print("age=" + age+",");
System.out.println("height=" + height + ",");
}
}
輸出
System.out: id=1,name=小明,sex=男,age=18,height=175,
System.out: id=2,name=小紅,sex=女,age=19,height=165,
System.out: id=3,name=小強,sex=男,age=20,height=185,
用gson進行簡單的轉換
package scut.learngson;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import com.google.gson.Gson;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Gson gson = new Gson();
EntityStudent student = new EntityStudent();
String json = "{\"id\":1,\"name\":\"小明\",\"sex\":\"男\",\"age\":18,\"height\":175}";
student = gson.fromJson(json,EntityStudent.class);//json資料轉為單個類實體
student.show();
String json1 = gson.toJson(student);//轉化為json
System.out.println(json1);
}
}
帶泛型的List裝類實體陣列資料
package scut.learngson;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import com.google.gson.reflect.TypeToken;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Gson gson = new Gson();
String json = "[{\"id\":1,\"name\":\"小明\",\"sex\":\"男\",\"age\":18,\"height\":175},{\"id\":2,\"name\":\"小紅\",\"sex\":\"女\",\"age\":19,\"height\":165},{\"id\":3,\"name\":\"小強\",\"sex\":\"男\",\"age\":20,\"height\":185}]";
List<EntityStudent> List = gson.fromJson(json, new TypeToken<List<EntityStudent>>(){}.getType());
//將JSON解析為帶泛型的list
for (int i= 0;i<List.size();i++) {
EntityStudent stu = List.get(i);
stu.show();
}//顯示實體資料
String json2 = gson.toJson(List);//轉換為json
System.out.println(json2);
}
}
結果:
2.用Gson解析複雜json資料
重點是要根據json資料裡面的結構寫出一個對應的javaBean,規則是:
1.json的大括號對應一個物件,物件裡面有key和value(值)。在Bean裡面的類屬性要和key同名。
2.json的方括號對應一個數組,所以在Bean裡面對應的也是陣列,資料裡面可以有值或者物件。
3.如果數組裡面只有值沒有key,就說明它只是一個純陣列,如果裡面有值有key,則說明是物件陣列。純陣列對應Bean裡面的陣列,物件陣列要在Bean裡面建立一個內部類,類屬性就是對應的物件裡面的key,建立了之後要建立一個這個內部類的物件,名字對應陣列名。
4.物件裡面巢狀物件時候,也要建立一個內部類,和物件陣列一樣,這個內部類物件的名字就是父物件的key
json資料(從有道API獲取到的):
{"translation":["車"],
"basic":
{ "us-phonetic":"kɑr",
"phonetic":"kɑː",
"uk-phonetic":"kɑː",
"explains":["n. 汽車;車廂","n. (Car)人名;(土)賈爾;(法、西)卡爾;(塞)察爾"]},
"query":"car",
"errorCode":0,
"web":[{"value":["汽車","車子","小汽車"],"key":"Car"},
{"value":["概念車","概念車","概念汽車"],"key":"concept car"},
{"value":["碰碰車","碰撞用汽車","碰碰汽車"],"key":"bumper car"}]
}
根據json資料的結構和key值寫的一個簡略的javabean
PS:這裡的javaBean不是一個正規的javaBean,因為類屬性都是public宣告的,這樣用來測試的話還可以,但是在實際應用中不安全,正規的javaBean可以參考下面Jackson解析複雜json資料的javaBean.
package scut.httpgson;
import java.util.List;
public class fanyi {
public String[] translation;
public basic basic;
public static class basic{
public String phonetic;
public String[] explains;
}
public String query;
public int errorCode;
public List<wb> web;
public static class wb{
public String[] value;
public String key;
}
public void show(){
for (int i = 0;i<translation.length;i++)
{
System.out.println(translation[i]);
}
System.out.println(basic.phonetic);
for (int i = 0;i<basic.explains.length;i++){
System.out.println(basic.explains[i]);
}
System.out.println(query);
System.out.println(errorCode);
for (int i = 0;i<web.size();i++){
for(int j = 0; j<web.get(i).value.length;j++)
{
System.out.println(web.get(i).value[j]);
}
System.out.println(web.get(i).key);
}
}
}
fanyi.java:
package scut.httpgson;
import java.util.List;
public class fanyi {
public String[] translation; //["車"]陣列
public basic basic; //basic物件裡面巢狀著物件,建立一個basic內部類物件
public static class basic{ //建立內部類
public String phonetic;
public String[] explains;
}
public String query;
public int errorCode;
public List<wb> web; //web是一個物件陣列,建立一個web內部類物件
public static class wb{
public String[] value;
public String key;
}
public void show(){
for (int i = 0;i<translation.length;i++)
{
System.out.println(translation[i]);}
System.out.println(basic.phonetic);
for (int i = 0;i<basic.explains.length;i++){
System.out.println(basic.explains[i]);
}
System.out.println(query);
System.out.println(errorCode);
for (int i = 0;i<web.size();i++){
for(int j = 0; j<web.get(i).value.length;j++)
{
System.out.println(web.get(i).value[j]);
}
System.out.println(web.get(i).key);
}
}
}
MainActivity:
package scut.httpgson;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;
import com.google.gson.Gson;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
public class MainActivity extends AppCompatActivity {
private TextView tv;
private String json;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv = (TextView) findViewById(R.id.tv);
findViewById(R.id.btnstart).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
new AsyncTask<String, Void, String>() {
@Override
protected String doInBackground(String... params) {
try {
URL url = new URL(params[0]);
URLConnection connection = url.openConnection();
InputStream is = connection.getInputStream();
InputStreamReader isr = new InputStreamReader(is,"utf-8");
BufferedReader bfr = new BufferedReader(isr);
json = bfr.readLine();
System.out.println(json);
Gson gson = new Gson();
fanyi fan = gson.fromJson(json,fanyi.class);
fan.show();
bfr.close();
isr.close();
is.close();
} catch (MalformedURLException e) {
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
}.execute("http://fanyi.youdao.com/openapi.do?keyfrom=Yanzhikai&key=2032414398&type=data&doctype=json&version=1.1&q=car");
}
});
}
輸出結果:
System.out: {"translation":["車"],"basic":{"us-phonetic":"kɑr","phonetic":"kɑː","uk-phonetic":"kɑː","explains":["n. 汽車;車廂","n. (Car)人名;(土)賈爾;(法、西)卡爾;(塞)察爾"]},"query":"car","errorCode":0,"web":[{"value":["汽車","小汽車","轎車"],"key":"Car"},{"value":["概念車","概念車","概念汽車"],"key":"concept car"},{"value":["碰碰車","碰撞用汽車","碰碰汽車"],"key":"bumper car"}]}
System.out: 車
System.out: kɑː
System.out: n. 汽車;車廂
System.out: n. (Car)人名;(土)賈爾;(法、西)卡爾;(塞)察爾
System.out: car
System.out: 0
System.out: 汽車
System.out: 小汽車
System.out: 轎車
System.out: Car
System.out: 概念車
System.out: 概念車
System.out: 概念汽車
System.out: concept car
System.out: 碰碰車
System.out: 碰撞用汽車
System.out: 碰碰汽車
System.out: bumper car
把有道翻譯的單詞car換成new,輸出:
System.out: {"translation":["新"],"basic":{"us-phonetic":"nu","phonetic":"njuː","uk-phonetic":"njuː","explains":["adj. 新的,新鮮的;更新的;初見的","adv. 新近","n. (New)人名;(英)紐"]},"query":"new","errorCode":0,"web":[{"value":["新的","新建","新品"],"key":"new"},{"value":["新世紀","新世紀音樂","新紀元運動"],"key":"NEW AGE"},{"value":["新罕布什爾","新罕布什爾州","新罕布什爾州"],"key":"New Hampshire"}]}
System.out: 新
System.out: njuː
System.out: adj. 新的,新鮮的;更新的;初見的
System.out: adv. 新近
System.out: n. (New)人名;(英)紐
System.out: new
System.out: 0
System.out: 新的
System.out: 新建
System.out: 新品
System.out: new
System.out: 新世紀
System.out: 新世紀音樂
System.out: 新紀元運動
System.out: NEW AGE
System.out: 新罕布什爾
System.out: 新罕布什爾州
System.out: 新罕布什爾州
System.out: New Hampshire
四、Jackson解析json
1.用Jackson簡單json的解析:
一個javaBean
和Gson解析不同,Jackson解析對應的javaBean必須把json資料裡面的所有key都弄出來對應好
package scut.learnjackson;
public class Student {
private int id;
private String name;
private String sex;
private int age;
private int height;
public void setId(int id){
this.id = id;
}
public int getId(){
return id;
}
public void setName(String name){
this.name = name;
}
public String getName(){
return name;
}
public void setSex(String sex){
this.sex = sex;
}
public String getSex(){
return sex;
}
public void setAge(int age){
this.age = age;
}
public int getAge(){
return age;
}
public void setHeight(int height){
this.height = height;
}
public int getHeight(){
return height;
}
public String toString(){
return id+" "+name+" "+sex+" "+age+" "+height;
}
}
解析簡單的json物件:
package scut.learnjackson;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.type.JavaType;
import java.io.IOException;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
String json = "{\"id\":1,\"name\":\"小明\",\"sex\":\"男\",\"age\":18,\"height\":175}";
ObjectMapper objectMapper = new ObjectMapper();
try {
Student student = objectMapper.readValue(json,Student.class);
System.out.println(student.toString());
} catch (IOException e) {
e.printStackTrace();
}
}
}
輸出:
1 小明 男 18 175
2.解析簡單的json物件陣列:
package scut.learnjackson;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.type.JavaType;
import java.io.IOException;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
String json = "[{\"id\":1,\"name\":\"小明\",\"sex\":\"男\",\"age\":18,\"height\":175},{\"id\":2,\"name\":\"小紅\",\"sex\":\"女\",\"age\":19,\"height\":165},{\"id\":3,\"name\":\"小強\",\"sex\":\"男\",\"age\":20,\"height\":185}]";
ObjectMapper objectMapper = new ObjectMapper();
try {
list = objectMapper.readValue(json,list.getClass());
JavaType javaType = objectMapper.getTypeFactory().constructParametricType(ArrayList.class,Student.class);
ArrayList<Student> list = objectMapper.readValue(json, javaType);//用ArrayList裝json陣列資料
System.out.println(list.toString());//ArrayList的toString方法
System.out.println(list.get(0).toString());//Student類的toString
} catch (IOException e) {
e.printStackTrace();
}
}
}
輸出:
[1 小明 男 18 175, 2 小紅 女 19 165, 3 小強 男 20 185]
1 小明 男 18 175
3.用Jackson解析複雜的json資料
json資料:
{"student":
[
{"id":1,"name":"小明","sex":"男","age":18,"height":175,"date":[2013,8,11]},
{"id":2,"name":"小紅","sex":"女","age":19,"height":165,"date":[2013,8,23]},
{"id":3,"name":"小強","sex":"男","age":20,"height":185,"date":[2013,9,1]}
],
"grade":"2"
}
建立對應的javaBean:
建立javaBean的對應規則和gson一樣
package scut.learnjackson;
import java.util.ArrayList;
import java.util.List;
class test {
private List<stu> student = new ArrayList<stu>();
private int grade;
public void setStudent(List<stu> student){
this.student = student;
}
public List<stu> getStudent(){
return student;
}
public void setGrade(int grade){
this.grade = grade;
}
public int getGrade(){
return grade;
}
private static class stu {
private int id;
private String name;
private String sex;
private int age;
private int height;
private int[] date;
public void setId(int id){
this.id = id;
}
public int getId(){
return id;
}
public void setName(String name){
this.name = name;
}
public String getName(){
return name;
}
public void setSex(String sex){
this.sex = sex;
}
public String getSex(){
return sex;
}
public void setAge(int age){
this.age = age;
}
public int getAge(){
return age;
}
public void setHeight(int height){
this.height = height;
}
public int getHeight(){
return height;
}
public void setDate(int[] date){
this.date = date;
}
public int[] getDate(){
return date;
}
}
public String tostring(){
String str = "";
for (int i = 0;i<student.size();i++){
str += student.get(i).getId() + " " + student.get(i).getName() + " " + student.get(i).getSex() + " " + student.get(i).getAge() + " " + student.get(i).getHeight() ;
for (int j = 0;j<student.get(i).getDate().length;j++) {
str += student.get(i).getDate()[j]+ " " ;
}
str += "\n";
}
str += "\n"+getGrade();
return str;
}
}
Mainactivity
package scut.learnjackson;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import org.codehaus.jackson.map.ObjectMapper;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ObjectMapper objectMapper = new ObjectMapper();
try {
InputStreamReader isr = new InputStreamReader(this.getClass().getClassLoader().getResourceAsStream("assets/" + "student.json"),"utf-8");
//從assets獲取json檔案
BufferedReader bfr = new BufferedReader(isr);
String line;
StringBuilder stringBuilder = new StringBuilder();
while ((line = bfr.readLine())!=null){
stringBuilder.append(line);
}//將JSON資料轉化為字串
System.out.println(stringBuilder.toString());
System.out.println(tes.tostring());
} catch (IOException e) {
e.printStackTrace();
}
}
}
輸出:
System.out: {"student": [ {"id":1,"name":"小明","sex":"男","age":18,"height":175,"date":[2013,8,11]}, {"id":2,"name":"小紅","sex":"女","age":19,"height":165,"date":[2013,8,23]}, {"id":3,"name":"小強","sex":"男","age":20,"height":185,"date":[2013,9,1]} ], "grade":"2"}
System.out: 1 小明 男 18 1752013 8 11
System.out: 2 小紅 女 19 1652013 8 23
System.out: 3 小強 男 20 1852013 9 1
System.out: 2
以上就是本人所總結的解析json資料的三種方法,如果要解析少量資料json資料的話建議使用Gson解析,方便快捷,如果解析大量json資料的話建議用Jackson解析,效能高效。