Android-json解析（二）：Jackson的使用
阿新 • • 發佈：2019-01-04
使用Jackson，主要是使用writeValueAsString和readValue這兩個方法。此外，Jackson的writeValue和readValue有很多種引數型別，適用於多中場合。
1、匯入依賴
compile 'com.fasterxml.jackson.core:jackson-databind:2.9.0.pr3'
compile 'com.fasterxml.jackson.core:jackson-core:2.9.0.pr3'
compile 'com.fasterxml.jackson.core:jackson-annotations:2.9.0.pr3'2、新增packagingOptions
因為jackson-core和jackson-databind有重複的檔案，重複載入會報錯。
android{
...
packagingOptions {
exclude 'META-INF/NOTICE' // will not include NOTICE file
exclude 'META-INF/LICENSE' // will not include LICENSE file
}
}3、工具類：
package com.example.administrator.gsondemo;
import 4、測試
Person 類：
package com.example.administrator.gsondemo;
/**
* Created by Administrator on 2017/5/9.
*/
public class Person {
private String name;
private int age;
private Birthday birthday;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Birthday getBirthday() {
return birthday;
}
public void setBirthday(Birthday birthday) {
this.birthday = birthday;
}
public Person() {
}
public Person(String name, int age, Birthday birthday) {
this.name = name;
this.age = age;
this.birthday = birthday;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
", birthday=" + birthday +
'}';
}
}
Birthday 類：
package com.example.administrator.gsondemo;
/**
* Created by Administrator on 2017/5/9.
*/
public class Birthday {
private int year;
private int month;
private int day;
public int getYear() {
return year;
}
public void setYear(int year) {
this.year = year;
}
public int getMonth() {
return month;
}
public void setMonth(int month) {
this.month = month;
}
public int getDay() {
return day;
}
public void setDay(int day) {
this.day = day;
}
public Birthday() {
}
public Birthday(int year, int month, int day) {
this.year = year;
this.month = month;
this.day = day;
}
@Override
public String toString() {
return "Birthday{" +
"year=" + year +
", month=" + month +
", day=" + day +
'}';
}
}
MainActivity 類：
package com.example.administrator.gsondemo;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
objectsToJson_Jackson();
objectToJson_Jackson();
}
/*------------------------------------Jackson----------------------------------*/
/**
* 單一物件的json生成與解析
*/
public void objectToJson_Jackson() {
Person p = new Person("zhaokaiqiang", 22, new Birthday(1992, 1, 19));
String jsonString = null;
try {
jsonString = JacksonUtil.obj2json(p);
} catch (Exception e) {
e.printStackTrace();
}
Log.e(TAG, "---------jackson單一物件生成字串--------");
Log.e(TAG, jsonString);
Log.e(TAG, jsonString instanceof String ? "型別===String" : "型別不為String");
Person person = null;
try {
person = JacksonUtil.json2pojo(jsonString, Person.class);
} catch (Exception e) {
e.printStackTrace();
}
Log.e(TAG, "---------jackson單一字串解析成物件--------");
Log.e(TAG, person.toString());
Log.e(TAG, "物件的名字：：：：" + person.getName());
}
/**
* 集合物件的json生成與解析
*/
public void objectsToJson_Jackson() {
Person person1 = new Person("zhaokaiqiang1", 21, new Birthday(1991, 1, 19));
Person person2 = new Person("zhaokaiqiang2", 22, new Birthday(1992, 2, 29));
Person person3 = new Person("zhaokaiqiang3", 23, new Birthday(1993, 3, 39));
ArrayList<Person> arrayList = new ArrayList<Person>();
arrayList.add(person1);
arrayList.add(person2);
arrayList.add(person3);
String jsonString = null;
try {
jsonString = JacksonUtil.obj2json(arrayList);
} catch (Exception e) {
e.printStackTrace();
}
Log.e(TAG, "---------jackson集合物件生成字串--------");
Log.e(TAG, jsonString);
Log.e(TAG, jsonString instanceof String ? "型別===String" : "型別不為String");
List<Person> persons = null;
try {
persons = JacksonUtil.json2list(jsonString, Person.class);
} catch (Exception e) {
e.printStackTrace();
}
Log.e(TAG, "---------jackson集合字串解析成物件--------");
Log.e(TAG, persons.toString());
Log.e(TAG, "物件的名字：：：：" + persons.get(0).getName());
}
}
5、問題及解答：
5.1 執行後報以下錯誤，請參照上面第二條：新增packagingOptions
Error:Execution failed for task ':app:transformResourcesWithMergeJavaResForDebug'.
> com.android.build.api.transform.TransformException: com.android.builder.packaging.DuplicateFileException: Duplicate files copied in APK META-INF/LICENSE
File1: C:\Users\Administrator\.gradle\caches\modules-2\files-2.1\com.fasterxml.jackson.core\jackson-annotations\2.9.0.pr3\dede10be4aaaa6893561372dc5196644268997b7\jackson-annotations-2.9.0.pr3.jar
File2: C:\Users\Administrator\.gradle\caches\modules-2\files-2.1\com.fasterxml.jackson.core\jackson-core\2.9.0.pr3\f9c6d5cfde33c589596d1f43200ec052a2c7c9c0\jackson-core-2.9.0.pr3.jar
File3: C:\Users\Administrator\.gradle\caches\modules-2\files-2.1\com.fasterxml.jackson.core\jackson-databind\2.9.0.pr3\41a8d484e0fe00102724d03090503ad212ee3c20\jackson-databind-2.9.0.pr3.jar5.2 Gson執行報錯
java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to...
異常原因:
作為方法傳入引數，Java編譯過程會將泛型物件型別擦除。
解決方法：
1、直接copy方法內程式碼直接使用，而不通過方法傳入
2、不使用
public static <T> List<T> getObjectList(String jsonString,Class<T> cls){
List<T> list = new ArrayList<T>();
try {
Gson gson = new Gson();
list = gson.fromJson(jsonString, new TypeToken<List<T>>(){}.getType());
} catch (Exception e) {
e.printStackTrace();
}
return list;
} 而使用以下：
public static <T> List<T> getObjectList(String jsonString,Class<T> cls){
List<T> list = new ArrayList<T>();
try {
Gson gson = new Gson();
JsonArray arry = new JsonParser().parse(jsonString).getAsJsonArray();
for (JsonElement jsonElement : arry) {
list.add(gson.fromJson(jsonElement, cls));
}
} catch (Exception e) {
e.printStackTrace();
}
return list;
}