How to serialize an object into a string

Question

I am able to serialize an object into a file and then restore it again as is shown in the next code snippet  I would like to serialize the object into a string and store into a database instead  Can anyone help me   LinkedList lt Diff match patch Patch gt  patches      whatever    FileOutputStream fileStream   new FileOutputStream  foo ser    ObjectOutputStream os   new ObjectOutputStream fileStream   os writeObject patches1   os close     FileInputStream fileInputStream   new FileInputStream  foo ser    ObjectInputStream oInputStream   new ObjectInputStream fileInputStream   Object one   oInputStream readObject    LinkedList lt Diff match patch Patch gt  patches3    LinkedList lt Diff match patch Patch gt   one  os close

User · Answer

Take a look at the java sql PreparedStatement class  specifically the function  http   java sun com javase 6 docs api java sql PreparedStatement html setBinaryStream int  20java io InputStream   Then take a look at the java sql ResultSet class  specifically the function  http   java sun com javase 6 docs api java sql ResultSet html getBinaryStream int   Keep in mind that if you are serializing an object into a database  and then you change the object in your code in a new version  the deserialization process can easily fail because your object s signature changed  I once made this mistake with storing a custom Preferences serialized and then making a change to the Preferences definition  Suddenly I couldn t read any of the previously serialized information   You might be better off writing clunky per property columns in a table and composing and decomposing the object in this manner instead  to avoid this issue with object versions and deserialization  Or writing the properties into a hashmap of some sort  like a java util Properties object  and then serializing the properties object which is extremely unlikely to change

User · Answer

Today the most obvious approach is to save the object s  to JSON   JSON is readable JSON is more readable and easier to work with than XML  A lot of Non-SQL databases that allow storing JSON directly  Your client already communicates with the server using JSON   If it doesn t  it is very likely a mistake    Example using Gson  Gson gson   new Gson    Person   persons   getArrayOfPersons    String json   gson toJson persons   System out println json     output     quot name quot   quot Tom quot   quot age quot  11    quot name quot   quot Jack quot   quot age quot  12   Person   personsFromJson   gson fromJson json  Person   class         class Person        public String name       public int age       Gson allows converting List directly  Examples can be easily googled  I prefer to convert lists to arrays first

User · Answer

Thanks for great and quick replies  I will gives some up votes inmediately to acknowledge your help  I have coded the best solution in my opinion based on your answers    LinkedList lt Patch gt  patches1   diff patch make text2  text1   try       ByteArrayOutputStream bos   new ByteArrayOutputStream        ObjectOutputStream os   new ObjectOutputStream bos       os writeObject patches1       String serialized patches1   bos toString        os close          ByteArrayInputStream bis   new ByteArrayInputStream serialized patches1 getBytes         ObjectInputStream oInputStream   new ObjectInputStream bis       LinkedList lt Patch gt  restored patches1    LinkedList lt Patch gt   oInputStream readObject                              patches1 equals restored patches1     oInputStream close      catch Exception ex        ex printStackTrace        Note i did not considered using JSON because is less efficient   Note  I will considered your advice about not storing serialized object as strings in the database but byte   instead

User · Answer

The serialised stream is just a sequence of bytes  octets   So the question is how to convert a sequence of bytes to a String  and back again  Further it needs to use a limited set of character codes if it is going to be stored in a database   The obvious solution to the problem is to change the field to a binary LOB  If you want to stick with a characer LOB  then you ll need to encode in some scheme such as base64  hex or uu

User · Answer

How about writing the data to a ByteArrayOutputStream instead of a FileOutputStream   Otherwise  you could serialize the object using XMLEncoder  persist the XML  then deserialize via XMLDecoder

User · Answer

If you re storing an object as binary data in the database  then you really should use a BLOB datatype   The database is able to store it more efficiently  and you don t have to worry about encodings and the like   JDBC provides methods for creating and retrieving blobs in terms of streams   Use Java 6 if you can  it made some additions to the JDBC API that make dealing with blobs a whole lot easier   If you absolutely need to store the data as a String  I would recommend XStream for XML-based storage  much easier than XMLEncoder   but alternative object representations might be just as useful  e g  JSON    Your approach depends on why you actually need to store the object in this way

User · Answer

You can use the build in classes sun misc Base64Decoder and sun misc Base64Encoder to convert the binary data of the serialize to a string  You das not need additional classes because it are build in

User · Answer

Use a O R framework such as hibernate

User · Answer

XStream provides a simple utility for serializing deserializing to from XML  and it s very quick   Storing XML CLOBs rather than binary BLOBS is going to be less fragile  not to mention more readable

User · Answer

Simple Solution worked for me  public static byte   serialize Object obj  throws IOException       ByteArrayOutputStream out   new ByteArrayOutputStream        ObjectOutputStream os   new ObjectOutputStream out       os writeObject obj       return out toByteArray

User · Answer

How about persisting the object as a blob

User · Answer

Sergio   You should use BLOB  It is pretty straighforward with JDBC    The problem with the second code you posted is the encoding   You should additionally encode the bytes to make sure none of them fails   If you still want to write it down into a String you can encode the bytes using java util Base64    Still you should use CLOB as data type because you don t know how long the serialized data is going to be   Here is a sample of how to use it   import java util    import java io             Usage sample serializing SomeClass instance      public class ToStringSample        public static void main  String    args    throws IOException                                                        ClassNotFoundException           String string   toString  new SomeClass              System out println   Encoded serialized version              System out println  string            SomeClass some     SomeClass   fromString  string            System out println    n nReconstituted object            System out println  some                     Read the object from Base64 string        private static Object fromString  String s   throws IOException                                                          ClassNotFoundException           byte    data   Base64 getDecoder   decode  s            ObjectInputStream ois   new ObjectInputStream                                           new ByteArrayInputStream   data              Object o    ois readObject            ois close            return o                Write the object to a Base64 string         private static String toString  Serializable o   throws IOException           ByteArrayOutputStream baos   new ByteArrayOutputStream            ObjectOutputStream oos   new ObjectOutputStream  baos            oos writeObject  o            oos close            return Base64 getEncoder   encodeToString baos toByteArray                   Test subject  A very simple class      class SomeClass implements Serializable        private final static long serialVersionUID   1     See Nick s comment below      int i      Integer MAX VALUE      String s    ABCDEFGHIJKLMNOP       Double d   new Double  -1 0        public String toString            return   SomeClass instance says  Don t worry                      I m healthy  Look  my data is i       i                      s       s      d       d            Output       C  samples gt javac   java  C  samples gt java ToStringSample Encoded serialized version rO0ABXNyAAlTb21lQ2xhc3MAAAAAAAAAAQIAA0kAAWlMAAFkdAASTGphdmEvbGFuZy9Eb3VibGU7T AABc3QAEkxqYXZhL2xhbmcvU3RyaW5nO3hwf    3NyABBqYXZhLmxhbmcuRG91YmxlgLPCSilr w QCAAFEAAV2YWx1ZXhyABBqYXZhLmxhbmcuTnVtYmVyhqyVHQuU4IsCAAB4cL wAAAAAAAAdAAQQUJ DREVGR0hJSktMTU5PUA     Reconstituted object SomeClass instance says  Don t worry  I m healthy  Look  my data is i   2147483647  s   ABCDEFGHIJKLMNOP  d   -1 0   NOTE  for Java 7 and earlier you can see the original answer here

User · Answer

you can use UUEncoding

User · Answer

Java8 approach  converting Object from to String  inspired by answer from OscarRyz  For de- encoding  java util Base64 is required and used   import java io ByteArrayInputStream  import java io ByteArrayOutputStream  import java io IOException  import java io ObjectInputStream  import java io ObjectOutputStream  import java io Serializable  import java util Base64  import java util Optional   final class ObjectHelper      private ObjectHelper         static Optional lt String gt  convertToString final Serializable object        try  final ByteArrayOutputStream baos   new ByteArrayOutputStream          ObjectOutputStream oos   new ObjectOutputStream baos           oos writeObject object         return Optional of Base64 getEncoder   encodeToString baos toByteArray            catch  final IOException e          e printStackTrace          return Optional empty                 static  lt T extends Serializable gt  Optional lt T gt  convertFrom final String objectAsString        final byte   data   Base64 getDecoder   decode objectAsString       try  final ObjectInputStream ois   new ObjectInputStream new ByteArrayInputStream data            return Optional of  T  ois readObject           catch  final IOException   ClassNotFoundException e          e printStackTrace          return Optional empty

[java] How to serialize an object into a string

Examples related to java

Examples related to serialization