我想使用Gson库来序列化和存储一个名为“Battery”的自定义类的对象。在Battery类中，我定义了另一个自定义对象的数组，即“Cannon”。这是我的两个班级：
Cannon.java：
import android.widget.ImageView;
public class Cannon {
private String id; // used for object storage
private int number; // Cannon number in battery
private ImageView icon;
private long utmEast, utmNorth; // Used to define cannon global location
private boolean isBase; // Defines if the cannon is base
private double flyingTime;
private int angle, side;
public Cannon() {
}
public Cannon(String id, int number, ImageView icon, String connectionNumber){
this.id = id;
this.number = number;
this.icon = icon;
this.connectionNumber = connectionNumber;
}
public String getId() {
return this.id;
}
public int getNumber() {
return this.number;
}
public ImageView getIcon() {
return this.icon;
}
public long getUtmNorth() {
return utmNorth;
}
public void setUtmNorth(long utmNorth) {
this.utmNorth = utmNorth;
}
public long getUtmEast() {
return utmEast;
}
public void setUtmEast(long utmEast) {
this.utmEast = utmEast;
}
public void setAsBase(boolean isBase) {
this.isBase = isBase;
}
public boolean isBaseCannon() {
return isBase;
}
}
Battery.java：
public class Battery {
private String id; // used for object storage
private final Cannon cannons[] = new Cannon[6];
public Battery(String id){
this.id = id;
}
public String getId() {
return this.id;
}
public Cannon[] getCannons() {
return cannons;
}
public void setCannon(Cannon cannon, int position) {
this.getCannons()[position] = cannon;
}
public Cannon getCannon(String cannonId) {
for (Cannon cn: this.getCannons()) {
if (cn.getId() == cannonId) {
return cn;
}
}
return null;
}
public Cannon getCannon(int position) {
return getCannons()[position];
}
}
这是我的Preferences类，它使用共享首选项来存储特定于应用程序的字段，包括使用Gson库的电池对象。
import android.content.Context;
import android.content.SharedPreferences;
import com.google.gson.Gson;
import net.adeveloper.firecontrol.data.Battery;
/** stores the user object in SharedPreferences */
public class Preferences {
/** This application's preferences label */
private static final String PREFS_NAME = "net.adeveloper.firecontrol.preferences";
/** This application's preferences */
private static SharedPreferences settings;
/** This application's settings editor*/
private static SharedPreferences.Editor editor;
/** Constructor takes an android.content.Context argument*/
private final Gson gson = new Gson();
/**************************************************/
private final Battery battery = new Battery(Reference.BATTERY_ID);
/**************************************************/
public Preferences(Context ctx){
if(settings == null){
settings = ctx.getSharedPreferences(PREFS_NAME,
Context.MODE_PRIVATE );
}
/*
* Get a SharedPreferences editor instance.
* SharedPreferences ensures that updates are atomic
* and non-concurrent
*/
editor = settings.edit();
// Initialize battery
String battery_json = gson.toJson(battery);
// store in SharedPreferences
String id = battery.getId(); // get storage key
editor.putString(id, battery_json);
editor.commit();
}
public Battery getBattery() {
String battery_json = settings.getString(Reference.BATTERY_ID, "");
Battery battery = gson.fromJson(battery_json, Battery.class);
return battery;
}
//...
}
我使用MainActivity中的首选项对象来存储应用程序字段：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//...
/********************************************************/
prefs = new Preferences(this.getApplicationContext());
/********************************************************/
然而，当它启动时，应用程序崩溃并输出Gson stackoverflowError：
02-10 16:39:03.110 13187-13187/net.adeveloper.firecontrol E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.StackOverflowError
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:355)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:117)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:72)
at com.google.gson.Gson.getAdapter(Gson.java:356)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.<init>(ReflectiveTypeAdapterFactory.java:82)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:81)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:118)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:72)
at com.google.gson.Gson.getAdapter(Gson.java:356)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.<init>(ReflectiveTypeAdapterFactory.java:82)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.cr
更新
我在setContentView之后将此代码添加到我的MainActivity，因为我使用的是Android版本为4.2.1的设备：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (android.os.Build.VERSION.SDK_INT > 9) {
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
}
//...
/********************************************************/
prefs = new Preferences(this.getApplicationContext());
/********************************************************/
现在stackoverflow异常已经消失了，但现在又出现了另一个问题，即由toJson（）和fromJson（）方法返回的我的Json字符串为null，当我通过电池类设置我的cannon对象时，使用Preference对象实际上无法访问它再次返回null：
Cannon cannon = new Cannon(id, number, icon, phone);
prefs.getBattery().setCannon(cannon, position);
if (prefs.getBattery().getCannons() == null) {
Log.d("Cannon", "NULL");
} else {
for (Cannon cn: prefs.getBattery().getCannons()) {
Log.d("Cannon", cn + "");
}
}
输出：
Cannon: null
Cannon: null
Cannon: null
Cannon: null
Cannon: null
Cannon: null
答案 0 :(得分：1)
我没有得到你想要达到的目标？但你可以
1.将objec转换为json
2.保存在SharedPreference中然后再生
3.再次可以从偏好中选择json
4.并转换为java Object
示例
class Test
{
int id = 1;
int name = "testing";
}
class Main{
Test t = new Test;
String s = ConvertToJson(t);
/* save the string in SharedPreferecne and you can get any
time string and convert again for eg.*/
Test t2 = ConvertToTest(TestJsonSring);
public Test ConvertToTest(String json) {
return new Gson().fromJson(json, Test.class);
}
public String ConvertToJson(Object object) {
Gson gson = new Gson();
return gson.toJson(object);
}
}