How do I serialize an object and save it to a file in Android

Question

Say I have some simple class and once it s instantiated as an object I want to be able to serialize its contents to a file  and retrieve it by loading that file at some later time    I m not sure where to start here  what do I need to do to serialize this object to a file   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              This is probably the easiest question in the world  because this is a really simple task in  NET  but in Android I m pretty new so I m completely lost

User · Accepted Answer

Saving  w o exception handling code    FileOutputStream fos   context openFileOutput fileName  Context MODE PRIVATE   ObjectOutputStream os   new ObjectOutputStream fos   os writeObject this   os close    fos close      Loading  w o exception handling code     FileInputStream fis   context openFileInput fileName   ObjectInputStream is   new ObjectInputStream fis   SimpleClass simpleClass    SimpleClass  is readObject    is close    fis close

User · Answer

I use 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 lt String gt  friends   new ArrayList lt  gt         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 lt String gt  newFriends   new ArrayList lt  gt         try           newFriends    ArrayList lt String gt   ObjectSerializer deserialize                  sharedPreferences getString  friends   ObjectSerializer serialize new ArrayList lt String gt              catch  IOException e            e printStackTrace              Log i     NewFriends   newFriends toString

User · Answer

Complete code with error handling and added file stream closes  Add it to your class that you want to be able to serialize and deserialize  In my case the class name is CreateResumeForm  You should change it to your own class name  Android interface Serializable is not sufficient to save your objects to the file  it only creates streams       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      Use it like this in your Activity    form   CreateResumeForm readFromFile this

User · Answer

I ve tried this 2 options  read write   with plain objects  array of objects  150 objects   Map   Option1   FileOutputStream fos   context openFileOutput fileName  Context MODE PRIVATE   ObjectOutputStream os   new ObjectOutputStream fos   os writeObject this   os close      Option2   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      Option 2 is twice quicker than option 1  The option 2 inconvenience is that you have to make specific code for read   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

User · Answer

I just made a class to handle this with Generics  so it can be used with all the object types that are serializable   public class SerializableManager                   Saves a serializable object                 param context The application context          param objectToSave The object to save          param fileName The name of the file          param  lt T gt  The type of the object               public static  lt T extends Serializable gt  void saveSerializable Context context  T objectToSave  String fileName            try               FileOutputStream fileOutputStream   context openFileOutput fileName  Context MODE PRIVATE               ObjectOutputStream objectOutputStream   new ObjectOutputStream fileOutputStream                objectOutputStream writeObject objectToSave                objectOutputStream close                fileOutputStream close              catch  IOException e                e printStackTrace                                    Loads a serializable object                 param context The application context          param fileName The filename          param  lt T gt  The object type                 return the serializable object               public static lt T extends Serializable gt  T readSerializable Context context  String fileName            T objectToReturn   null           try               FileInputStream fileInputStream   context openFileInput fileName               ObjectInputStream objectInputStream   new ObjectInputStream fileInputStream               objectToReturn    T  objectInputStream readObject                 objectInputStream close                fileInputStream close              catch  IOException   ClassNotFoundException e                e printStackTrace                       return objectToReturn                        Removes a specified file                 param context The application context          param filename The name of the file               public static void removeSerializable Context context  String filename            context deleteFile filename

User · Answer

You must add an ObjectSerialization class to your program the following may work      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  lt  bytes length  i              strBuf append  char     bytes i   gt  gt  4   amp  0xF      int   a              strBuf append  char     bytes i    amp  0xF      int   a                 return strBuf toString       public static byte   decodeBytes String str        byte   bytes   new byte str length     2       for  int i   0  i  lt  str length    i  2            char c   str charAt i           bytes i 2     byte    c -  a    lt  lt  4           c   str charAt i 1           bytes i 2      c -  a              return bytes         if you are using to store an array with SharedPreferences than use following -  SharedPreferences sharedPreferences   this getSharedPreferences getPackageName   MODE PRIVATE     To Serialize -  sharedPreferences putString  name  ObjectSerializer serialize array      To Deserialize -  newarray    CAST IT TO PROPER TYPE  ObjectSerializer deSerialize sharedPreferences getString name  null

[android] How do I serialize an object and save it to a file in Android?

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