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<Diff_match_patch.Patch> 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<Diff_match_patch.Patch> patches3 = (LinkedList<Diff_match_patch.Patch>) one;
os.close();
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>javac *.java
C:\samples>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
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.
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<Patch> 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<Patch> restored_patches1 = (LinkedList<Patch>) 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.
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<String> 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 <T extends Serializable> Optional<T> 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();
}
}
}
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.
How about persisting the object as a blob
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.
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.
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.
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.
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();
}
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: [{"name":"Tom","age":11},{"name":"Jack","age":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.
you can use UUEncoding
Related
This question already has an answer here:
Writing LinkedList into text file via ObjectOutputStream but output is garbage
(1 answer)
Closed 1 year ago.
I am using Spring framework, and use streamresolution to return a .txt file for user to download.
The result of data is fine, however, there is a 't' in front of every column of data,
and besides the last column, there is a 'w' in the end of every column.
I can't not understand why because the data seems fine, and I didn't told the program to create the letter.
Here is my code:
// A list of String, which are the data, it might looks like 20200810,a,b,c,100,55,.....
// the whole is a String contains comma
List<String> dataList = (List<String>) parameters.get("myData");
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
StreamingResolution streamingResolution = null;
ObjectOutputStream oos = new ObjectOutputStream(outputStream);
oos.writeObject("\n");
for (String s : dataList) {
oos.writeObject(s.trim());
oos.writeUTF("\n");
}
streamingResolution = new StreamingResolution("text/plain", new ByteArrayInputStream(outputStream.toByteArray()));
streamingResolution.setCharacterEncoding(CharEncoding.UTF_8);
String year = Integer.toString((Integer.parseInt(end.substring(0, 4));
String day = year + end.substring(4, 6);
oos.close();
return streamingResolution.setFilename(day + ".txt");
while I download the data, 202108.txt
it might looks like
t ?0210810,a,b,c,100,55w
t ?0210810,d,e,f,99,60
could anyone please tell me why there would be a 't' in the front
and a 'w' in the end?
And how to fix this?
Thanks a lot.
This code uses an ObjectOutputStream, which is used to write serialized Java data in a binary format. It is not a plain text format, and should not be used in this way. The extra characters are bytes that are defined in the Java Object Serialization Specification.
To write plain text, you can use the java.io.PrintStream class instead. For example:
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
PrintStream printStream = new PrintStream(outputStream, false, StandardCharsets.UTF_8);
printStream.println();
for (String s : dataList) {
printStream.println(s.trim());
}
printStream.flush();
StreamingResolution streamingResolution = new StreamingResolution("text/plain", new ByteArrayInputStream(outputStream.toByteArray()));
streamingResolution.setCharacterEncoding(CharEncoding.UTF_8);
Note that I also simplified the code by moving the streamingResolution local variable declaration to where it is assigned.
This is a straightforward translation of the code provided, to show you how to use the PrintStream class, however it may not be the best way to write it. The StreamingResolution class appears to be part of the Stripes Framework. It is intended for streaming large responses to the client. However, this implementation does not actually stream the response, it accumulates it into a byte array. A better way to implement this would be to subclass the StreamingResponse class, as described in the Stripe documentation, to write directly to the response:
return new StreamingResolution("text/plain") {
public void stream(HttpServletResponse response) throws Exception {
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
out.println();
for (String s : dataList) {
out.println(s.trim());
}
out.flush();
}
}.setFilename(day + ".txt");
I was creating a simple android application in which I am converting an object to String. How can I re-convert the object from the string?
I am converting my object to String using the following line of code.
String convertedString = object.toString();
You can't**, because that is not what the toString method is for. It's used to make a readable representation of your Object, but it's not meant for saving and later reloading.
What you are looking for instead is Serialization. See this tutorial here to get started:
http://www.tutorialspoint.com/java/java_serialization.htm
** Technically you could, but you shouldn't.
You can do it in two ways:
Java Serialization
Using Gson library (more simple), remember the the purpose of this lib is to convert simply json to object and viceversa when working with REST services.
Hope it helps
You can use Serialization to convert object to string and vise versa:
String serializedObject = "";
// serialize the object
try {
ByteArrayOutputStream bo = new ByteArrayOutputStream();
ObjectOutputStream so = new ObjectOutputStream(bo);
so.writeObject(myObject);
so.flush();
serializedObject = bo.toString();
} catch (Exception e) {
System.out.println(e);
}
// deserialize the object
try {
byte b[] = serializedObject.getBytes();
ByteArrayInputStream bi = new ByteArrayInputStream(b);
ObjectInputStream si = new ObjectInputStream(bi);
MyObject obj = (MyObject) si.readObject();
} catch (Exception e) {
System.out.println(e);
}
Use Java Serialization for doing same.
Go with below link for better understand how to convert java object.
Ex. http://www.geeksforgeeks.org/serialization-in-java/
Also You can go with this link:
How to convert the following json string to java object?
Updates:
For now using a Map. Class that wants to send something to other instance sends the object, the routing string.
Use an object stream, use Java serializable to write the object to servlet.
Write String first and then the object.
Receiving servlet wraps input stream around a ObjectInputStream. Reads string first and then the Object. Routing string decides were it goes.
A more generic way might have been to send a class name and its declared method or a Spring bean name, but this was enough for us.
Original question
Know the basic way but want details of steps. Also know I can use Jaxb or RMI or EJB ... but would like to do this using pure serialization to a bytearray and then encode that send it from servlet 1 in jvm 1 to servlet 2 in jvm 2 (two app server instances in same LAN, same java versions and jars set up in both J2EE apps)
Basic steps are (Approcah 1) :-
serialize any Serializable object to a byte array and make a string. Exact code see below
Base64 output of 1. Is it required to base 64 or can skip step 2?
use java.util.URLEncode.encode to encode the string
use apache http components or URL class to send from servlet 1 to 2 after naming params
on Servlet 2 J2EE framework would have already URLDecoced it, now just do reverse steps and cast to object according to param name.
Since both are our apps we would know the param name to type / class mapping. Basically looking for the fastest & most convenient way of sending objects between JVMs.
Example :
POJO class to send
package tst.ser;
import java.io.Serializable;
public class Bean1 implements Serializable {
/**
* make it 2 if add something without default handling
*/
private static final long serialVersionUID = 1L;
private String s;
public String getS() {
return s;
}
public void setS(String s) {
this.s = s;
}
}
* Utility *
package tst.ser;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.URLEncoder;
public class SerUtl {
public static String serialize(Object o) {
String s = null;
ObjectOutputStream os = null;
try {
os = new ObjectOutputStream(new ByteArrayOutputStream());
os.writeObject(o);
s = BAse64.encode(os.toByeArray());
//s = URLEncoder.encode(s, "UTF-8");//keep this for sending part
} catch (Exception e) {
// TODO: logger
e.printStackTrace();
return null;
} finally {
// close OS but is in RAM
try {
os.close();// not required in RAM
} catch (Exception e2) {// TODO: handle exception logger
}
os = null;
}
return s;
}
public static Object deserialize(String s) {
Object o = null;
ObjectInputStream is = null;
try {
// do base 64 decode if done in serialize
is = new ObjectInputStream(new ByteArrayInputStream(
Base64.decode(s)));
o = is.readObject();
} catch (Exception e) {
// TODO: logger
e.printStackTrace();
return null;
} finally {
// close OS but is in RAM
try {
is.close();// not required in RAM
} catch (Exception e2) {// TODO: handle exception logger
}
is = null;
}
return o;
}
}
**** sample sending servlet ***
Bean1 b = new Bean1(); b.setS("asdd");
String s = SerUtl.serialize(b);
//do UrlEncode.encode here if sending lib does not.
HttpParam p = new HttpParam ("bean1", s);
//http components send obj
**** sample receiving servlet ***
String s = request.getParameter("bean1");
Bean1 b1 = (Beean1)SerUtl.deserialize(s);
Serialize any Serializable object with to a byte array
Yes.
and make a string.
No.
Exact statements see below
os = new ObjectOutputStream(new ByteArrayOutputStream());
os.writeObject(o);
s = os.toString();
// s = Base64.encode(s);//Need this some base 64 impl like Apache ?
s = URLEncoder.encode(s, "UTF-8");
These statements don't even do what you have described, which is in any case incorrect. OutputStream.toString() doesn't turn any bytes into Strings, it just returns a unique object identifier.
Base64 output of 1.
The base64 output should use the byte array as the input, not a String. String is not a container for binary data. See below for corrected code.
ByteArrayOutputStream baos = new ByteArrayOutputStream();
os = new ObjectOutputStream(baos);
os.writeObject(o);
os.close();
s = Base64.encode(baos.toByeArray()); // adjust to suit your API
s = URLEncoder.encode(s, "UTF-8");
This at least accomplishes your objective.
Is it required to base 64 or can skip step 2?
If you want a String you must encode it somehow.
Use java.util.URLEncode.encode to encode the string
This is only necessary if you're sending it as a GET or POST parameter.
Use apache http components or URL class to send from servlet 1 to 2 after naming params
Yes.
On Servlet 2 J2EE framework would have already URLDecoded it, now just do reverse steps and cast to object according to param name.
Yes, but remember to go directly from the base64-encoded string to the byte array, no intermediate String.
Basically looking for the fastest & most convenient way of sending objects between JVMs.
These objectives aren't necessarily reconcilable. The most convenient these days is probably XML or JSON but I doubt that these are faster than Serialization.
os = null;
Setting references that are about to fall out of scope to null is pointless.
HttpParam p = new HttpParam ("bean1", s);
It's possible that HttpParam does the URLEncoding for you. Check this.
You need not convert to string. You can post the binary data straight to the servlet, for example by creating an ObjectOutputStream on top of a HttpUrlConnection's outputstream. Set the request method to POST.
The servlet handling the post can deserialize from an ObjectStream created from the HttpServletRequest's ServletInputStream.
I'd recommend JAXB any time over binary serialization, though. The frameworks are not only great for interoperability, they also speed up development and create more robust solutions.
The advantages I see are way better tooling, type safety, and code generation, keeping your options open so you can call your code from another version or another language, and easier debugging. Don't underestimate the cost of hard to solve bugs caused by accidentally sending the wrong type or doubly escaped data to the servlet. I'd expect the performance benefits to be too small to compensate for this.
Found this Base64 impl that does a lot of the heavy lifting for me : http://iharder.net/base64
Has utility methods :
String encodeObject(java.io.Serializable serializableObject, int options )
Object decodeToObject(String encodedObject, int options, final ClassLoader loader )
Using :
try {
String dat = Base64.encodeObject(srlzblObj, options);
StringBuilder data = new StringBuilder().append("type=");
data.append(appObjTyp).append("&obj=").append(java.net.URLEncoder.encode(dat, "UTF-8"));
Use the type param to tell the receiving JVM what type of object I'm sending. Each servlet/ jsps at most receives 4 types, usually 1. Again since its our own app and classes that we are sending this is quick (as in time to send over the network) and simple.
On the other end unpack it by :
String objData = request.getParameter("obj");
Object obj = Base64.decodeToObject(objData, options, null);
Process it, encode the result, send result back:
reply = Base64.encodeObject(result, options);
out.print("rsp=" + reply);
Calling servlet / jsp gets the result:
if (reply != null && reply.length() > 4) {
String objDataFromServletParam = reply.substring(4);
Object obj = Base64.decodeToObject(objDataFromServletParam, options, null);
options can be 0 or Base64.GZIP
You can use JMS as well.
Apache Active-MQ is one good solution. You will not have to bother with all this conversion.
/**
* #param objectToQueue
* #throws JMSException
*/
public void sendMessage(Serializable objectToQueue) throws JMSException
{
ObjectMessage message = session.createObjectMessage();
message.setObject(objectToQueue);
producerForQueue.send(message);
}
/**
* #param objectToQueue
* #throws JMSException
*/
public Serializable receiveMessage() throws JMSException
{
Message message = consumerForQueue.receive(timeout);
if (message instanceof ObjectMessage)
{
ObjectMessage objMsg = (ObjectMessage) message;
Serializable sobject = objMsg.getObject();
return sobject;
}
return null;
}
My point is do not write custom code for Serialization, iff it can be avoided.
When you use AMQ, all you need to do is make your POJO serializable.
Active-MQ functions take care of serialization.
If you want fast response from AMQ, use vm-transport. It will minimize n/w overhead.
You will automatically get benefits of AMQ features.
I am suggesting this because
You have your own Applications running on network.
You need a mechanism to transfer objects.
You will need a way to monitor it as well.
If you go for custom solution, you might have to solve above things yourselves.
Is it possible to write objects in Java to a binary file? The objects I want to write would be 2 arrays of String objects. The reason I want to do this is to save persistent data. If there is some easier way to do this let me know.
You could
Serialize the Arrays, or a class
that contains the arrays.
Write the arrays as two lines in a formatted
way, such as JSON,XML or CSV.
Here is some code for the first one (You could replace the Queue with an array)
Serialize
public static void main(String args[]) {
String[][] theData = new String[2][1];
theData[0][0] = ("r0 c1");
theData[1][0] = ("r1 c1");
System.out.println(theData.toString());
// serialize the Queue
System.out.println("serializing theData");
try {
FileOutputStream fout = new FileOutputStream("thedata.dat");
ObjectOutputStream oos = new ObjectOutputStream(fout);
oos.writeObject(theData);
oos.close();
}
catch (Exception e) { e.printStackTrace(); }
}
Deserialize
public static void main(String args[]) {
String[][] theData;
// unserialize the Queue
System.out.println("unserializing theQueue");
try {
FileInputStream fin = new FileInputStream("thedata.dat");
ObjectInputStream ois = new ObjectInputStream(fin);
theData = (Queue) ois.readObject();
ois.close();
}
catch (Exception e) { e.printStackTrace(); }
System.out.println(theData.toString());
}
The second one is more complicated, but has the benefit of being human as well as readable by other languages.
Read and Write as XML
import java.beans.XMLEncoder;
import java.beans.XMLDecoder;
import java.io.*;
public class XMLSerializer {
public static void write(String[][] f, String filename) throws Exception{
XMLEncoder encoder =
new XMLEncoder(
new BufferedOutputStream(
new FileOutputStream(filename)));
encoder.writeObject(f);
encoder.close();
}
public static String[][] read(String filename) throws Exception {
XMLDecoder decoder =
new XMLDecoder(new BufferedInputStream(
new FileInputStream(filename)));
String[][] o = (String[][])decoder.readObject();
decoder.close();
return o;
}
}
To and From JSON
Google has a good library to convert to and from JSON at http://code.google.com/p/google-gson/ You could simply write your object to JSOn and then write it to file. To read do the opposite.
You can do it using Java's serialization mechanism, but beware that serialization is not a good solution for long-term persistent storage of objects. The reason for this is that serialized objects are very tightly coupled to your Java code: if you change your program, then the serialized data files become unreadable, because they are not compatible anymore with your Java code. Serialization is good for temporary storage (for example for an on-disk cache) or for transferring objects over a network.
For long-term storage, you should use a standard and well-documented format (for example XML, JSON or something else) that is not tightly coupled to your Java code.
If, for some reason, you absolutely want to use a binary format, then there are several options available, for example Google protocol buffers or Hessian.
One possibility besides serialization is to write Objects to XML files to make them more human-readable. The XStream API is capable of this and uses an approach that is similar to serialization.
http://x-stream.github.io/
If you want to write arrays of String, you may be better off with a text file. The advantage of using a text file is that it can be easily viewed, edited and is usuable by many other tools in your system which mean you don't have to have to write these tools yourself.
You can also find that a simple text format will be faster and more compact than using XML or JSON. Note: Those formats are more useful for complex data structures.
public static void writeArray(PrintStream ps, String... strings) {
for (String string : strings) {
assert !string.contains("\n") && string.length()>0;
ps.println(strings);
}
ps.println();
}
public static String[] readArray(BufferedReader br) throws IOException {
List<String> strings = new ArrayList<String>();
String string;
while((string = br.readLine()) != null) {
if (string.length() == 0)
break;
strings.add(string);
}
return strings.toArray(new String[strings.size()]);
}
If your start with
String[][] theData = { { "a0 r0", "a0 r1", "a0 r2" } {"r1 c1"} };
This could result in
a0 r0
a0 r1
a0 r2
r1 c1
As you can see this is easy to edit/view.
This makes some assumptions about what a string can contain (see the asset). If these assumptions are not valid, there are way of working around this.
You need to write object, not class, right? Because classes are already compiled to binary .class files.
Try ObjectOutputStream, there's an example
http://java.sun.com/javase/6/docs/api/java/io/ObjectOutputStream.html
Is it possible to ObjectOutputStream/ObjectInputStream an internal class? I can write it OK, and examine the created file, but when I try to read it back in using ObjectInputStream, I get an EOFException just trying to read an Object o = oos.readObject();
I use the same File object to open both streams, so that's not the problem.
It seems to be independant of the nature of the internal Class - a class with just a public int fails identically to a more complex class.
I have to move on, and create a regular class, and instantiate in the sender class, but I hate to walk away not knowing if it is possible, and if not why not.
Update: Related issues that were the cause of the problem:
A. You cannot re-open a file written with an ObjectOutputStream and append: a second header is written and corrupts the file.
B. Serializing a HashMap using ByteOutputStream to do a hash digest doesn't work, because when you read the HashMap back in from a ObjectOutputStream file, you may very well get a different byte[] from ByteOutputStream because of variations in pair order: the content is the same, but the byte[] (and so the hash disgest) is not.
Hope this helps someone save some time.
This one works for me. Please look for any differences to your solution.
public class Example implements Serializable {
public static void main(String[] args) throws IOException, ClassNotFoundException {
new Example().run();
}
private void run() throws IOException, ClassNotFoundException {
Inner inner = new Inner();
inner.x = 5;
ByteArrayOutputStream out = new ByteArrayOutputStream();
ObjectOutputStream outputStream = new ObjectOutputStream( out );
outputStream.writeObject( inner );
ByteArrayInputStream in = new ByteArrayInputStream( out.toByteArray() );
ObjectInputStream inputStream = new ObjectInputStream( in );
Inner inner2 = (Inner) inputStream.readObject();
System.out.println( inner2.x );
}
class Inner implements Serializable {
int x;
}
}
Can you include a small bit of sample code? The most obvious explanation is that you're not closing / flushing the output stream before you try to read it back in.