Question

假设我有一些简单的类，一旦它被实例化为一个对象，我希望能够将其内容序列化为一个文件，并在稍后加载该文件来检索它...我不知道在哪里从这里开始，我需要做什么才能将此对象序列化为文件？

public class SimpleClass {
   public string name;
   public int id;
   public void save() {
       /* wtf do I do here? */
   }
   public static SimpleClass load(String file) {
       /* what about here? */
   }
}

这可能是世界上最简单的问题，因为这在.NET中是一个非常简单的任务，但在Android中我很新，所以我完全迷失了。

Answer 1

保存（没有异常处理代码）：

FileOutputStream fos = context.openFileOutput(fileName, Context.MODE_PRIVATE);
ObjectOutputStream os = new ObjectOutputStream(fos);
os.writeObject(this);
os.close();
fos.close();

加载（没有异常处理代码）：

FileInputStream fis = context.openFileInput(fileName);
ObjectInputStream is = new ObjectInputStream(fis);
SimpleClass simpleClass = (SimpleClass) is.readObject();
is.close();
fis.close();

Answer 2

我尝试了这2个选项（读/写），普通对象，对象数组（150个对象），Map：

<强>选项1：

FileOutputStream fos = context.openFileOutput(fileName, Context.MODE_PRIVATE);
ObjectOutputStream os = new ObjectOutputStream(fos);
os.writeObject(this);
os.close();

<强>选项2：

SharedPreferences mPrefs=app.getSharedPreferences(app.getApplicationInfo().name, Context.MODE_PRIVATE);
SharedPreferences.Editor ed=mPrefs.edit();
Gson gson = new Gson(); 
ed.putString("myObjectKey", gson.toJson(objectToSave));
ed.commit();

选项2比选项1快两倍

选项2的不便之处在于您必须为阅读制作特定代码：

Gson gson = new Gson();
JsonParser parser=new JsonParser();
//object arr example
JsonArray arr=parser.parse(mPrefs.getString("myArrKey", null)).getAsJsonArray();
events=new Event[arr.size()];
int i=0;
for (JsonElement jsonElement : arr)
    events[i++]=gson.fromJson(jsonElement, Event.class);
//Object example
pagination=gson.fromJson(parser.parse(jsonPagination).getAsJsonObject(), Pagination.class);

Answer 3

我刚用Generics创建了一个类来处理它，所以它可以用于所有可序列化的对象类型：

Q_SLOTS

Answer 4

关闭错误处理和添加的文件流的完整代码。将它添加到您希望能够序列化和反序列化的类中。在我的例子中，班级名称是CreateResumeForm。您应该将其更改为您自己的类名。 Android接口Serializable不足以将对象保存到文件中，它只会创建流。

// Constant with a file name
public static String fileName = "createResumeForm.ser";

// Serializes an object and saves it to a file
public void saveToFile(Context context) {
    try {
        FileOutputStream fileOutputStream = context.openFileOutput(fileName, Context.MODE_PRIVATE);
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
        objectOutputStream.writeObject(this);
        objectOutputStream.close();
        fileOutputStream.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}


// Creates an object by reading it from a file
public static CreateResumeForm readFromFile(Context context) {
    CreateResumeForm createResumeForm = null;
    try {
        FileInputStream fileInputStream = context.openFileInput(fileName);
        ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
        createResumeForm = (CreateResumeForm) objectInputStream.readObject();
        objectInputStream.close();
        fileInputStream.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
    catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
    return createResumeForm;
}

在Activity：

中使用它

form = CreateResumeForm.readFromFile(this);

Answer 5

我使用SharePrefrences：

package myapps.serializedemo;

import android.content.Context;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

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);

//Create the SharedPreferences
    SharedPreferences sharedPreferences = this.getSharedPreferences("myapps.serilizerdemo", Context.MODE_PRIVATE);
    ArrayList<String> friends = new ArrayList<>();
    friends.add("Jack");
    friends.add("Joe");
    try {

 //Write / Serialize
 sharedPreferences.edit().putString("friends",
    ObjectSerializer.serialize(friends)).apply();
    } catch (IOException e) {
        e.printStackTrace();
    }
//READ BACK
    ArrayList<String> newFriends = new ArrayList<>();
    try {
        newFriends = (ArrayList<String>) ObjectSerializer.deserialize(
                sharedPreferences.getString("friends", ObjectSerializer.serialize(new ArrayList<String>())));
    } catch (IOException e) {
        e.printStackTrace();
    }
    Log.i("***NewFriends", newFriends.toString());
}
}

Answer 6

您必须将ObjectSerialization类添加到程序中，以下方法可能会起作用

    import java.io.ByteArrayInputStream;
    import java.io.ByteArrayOutputStream;
    import java.io.IOException;
    import java.io.ObjectInputStream;
    import java.io.ObjectOutputStream;
    import java.io.Serializable;

    public class ObjectSerializer {

public static String serialize(Serializable obj) throws IOException {
    if (obj == null) return "";
    try {
        ByteArrayOutputStream serialObj = new ByteArrayOutputStream();
        ObjectOutputStream objStream = new ObjectOutputStream(serialObj);
        objStream.writeObject(obj);
        objStream.close();
        return encodeBytes(serialObj.toByteArray());
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

public static Object deserialize(String str) throws IOException {
    if (str == null || str.length() == 0) return null;
    try {
        ByteArrayInputStream serialObj = new ByteArrayInputStream(decodeBytes(str));
        ObjectInputStream objStream = new ObjectInputStream(serialObj);
        return objStream.readObject();
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

public static String encodeBytes(byte[] bytes) {
    StringBuffer strBuf = new StringBuffer();

    for (int i = 0; i < bytes.length; i++) {
        strBuf.append((char) (((bytes[i] >> 4) & 0xF) + ((int) 'a')));
        strBuf.append((char) (((bytes[i]) & 0xF) + ((int) 'a')));
    }

    return strBuf.toString();
}

public static byte[] decodeBytes(String str) {
    byte[] bytes = new byte[str.length() / 2];
    for (int i = 0; i < str.length(); i+=2) {
        char c = str.charAt(i);
        bytes[i/2] = (byte) ((c - 'a') << 4);
        c = str.charAt(i+1);
        bytes[i/2] += (c - 'a');
    }
    return bytes;
}

}

如果您要使用SharedPreferences存储数组，而不要使用以下命令：-

SharedPreferences sharedPreferences = this.getSharedPreferences(getPackageName(),MODE_PRIVATE);

要序列化：-

sharedPreferences.putString("name",ObjectSerializer.serialize(array));

要反序列化：-

newarray = (CAST_IT_TO_PROPER_TYPE) ObjectSerializer.deSerialize(sharedPreferences.getString(name),null);

如何序列化对象并将其保存到Android中的文件？

6 个答案: