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Store byte array and string in same file

Earlier I was storing only string in my file which can be store in SD card now I would to store byte[] also in same files. So do I just need to store normal to the file like this:
for string:- bufferWritter.write(data);
for bytes:- FileUtils.writeByteArrayToFile(new File("pathname"), myByteArray)
or fos.write(myByteArray);
So if I do like that then how can I differ message whether it is string or byte[].
Even I would like to know that is this is a good way to do?

You would need to write some sort of header to your file which should state what it does represent.
If you have multiple items in one file, also specify the length of the data parts.
[byte] sort of data (0=String, 1=Image)
And then the actual data.
But I would recommend you use a different format like json or make a serializable object.

I would give a try to some JSON implementation (maybe GSON? or some alternative) so you can have stored mixed data types in one file or write your own de/serialization routine so you can store whole objects.
Note: if you implement Serializable interface by a class that represent object to be stored, don't forget to re-generate UUID each time you change contents of that class, it will save you some time figuring out what went wrong

Partial deserialization of a huge binary file - Java

This is my first question to StackOverflow. Please let me know if the question is not clear and need any more details.
I have a class which has three attributes like this:
class SampleClass {
long [] field1;
float[] field2;
float[] field3;
}
A huge SampleClass object is built(with about a billion entries for each array). This object is serialized in one host and the serialized file is uploaded to another machine. Now I want to deserialize only a portion of the file so that I can get a smaller SampleClass object with about 10 indices filled for each field and not the complete object. Because this machine does not have enough capacity to load such a huge object in memory. Is this possible?
The object is serialized using JAVA's writeObject method and it is done by a different utility and so I have no control over it. Thanks in advance.

Forget using the Java serialization API - it's only designed to deserialize everything. If you have no control over how the serialized file is generated, then you should consider parsing the serialized file yourself and extracting the necessary parts - it's not really that hard.
The Java serialization format is well-documented (see e.g. official docs, informative article), and tools exist to parse the format (e.g. Serialysis, jdeserialize) though it isn't particularly hard to write your own tool based on the format spec.
Once you can parse the serialized data, you can simply extract what you need and skip over what you don't need.

Your best bet is to actually serialize only the portion you need, given that you cannot control/override serialization itself. On the machine which serialized entire file and is able to deserialize it:
1) load entire file into object
2) create new object of SampleClass
3) copy elements from required region in each array to blank SampleClass object
4) serialize this smaller version
If it helps any, fields can be made transient so they will not be serialized.
Still, it looks to me that this object should be in database:
It does not fit virtual memory
only portion of it is required at given time.
So you could use hard disk to store it and queries to get required portions.

save and retrieve multiple of arraylists to a file

Hi i was wondering if this was possible. i have 5 multiple array lists. after i add information to each array lists is it possible to save this as a single file using filechooser. i have 5 arraylist which i have created as a object from a different class.
hotelArrayObjects.getDahabArray()
hotelArrayObjects.getRomeArray()
hotelArrayObjects.getParisArray()
hotelArrayObject.getBerlinArray()
hotelArrayObjects.getNiceArray()
wondering if there was any way to do this. I was thinking of using Filechooser to make it more user friendly and easier to retrieve.
Any tips on how to tackle this problem?

You can use java.io.ObjectOutputStream and its subclasses for writing objects to files. You can read them back with java.io.ObjectInputStream and its subclasses. There are readObject() and writeObject() methods in these classes that you can use. Note that if you want to write an object to a file, the defining class of that object should be serializable. In you case, objects that you store in the ArrayList should be serializable.
Java mechanisms for storing and retrieving objects does not need the file to be selected with a FileChooser. You can use java.io.File class for opening a stream to your file.

If you want to save the information within an arraylist, you can do a few forloops then use a file writer
String s1;
for(int i=0; i<arraylist.length(); i++) {
s1+=arraylist.get(i);
}
repeat repeat
then use something like this:
String finalString = s1+s2+s3+s4+s5;
FileWriter fwrite = new FileWriter("hotels.txt");
BufferedWriter out = new BufferedWriter(fwrite);
out.write(finalString);
Then you can use the JFileChooser to save that file.

Java Object Array IO

I have an Array of Objects called "person" and i need to save that data, Is there a way to output an array and then input it back into the program. I have tried simply outputting the raw String and int data that makes up each "person" and the program never writes that data to the specified txt file. Is there a method or function that can write raw object data and then retrieve it?

You should have a look to ObjectOutputStream and ObjectOutputStream and the Serializable interface. What you are trying to do is to serialize your data to a file and load (deserialize) it back again.

You can use standard Java serialisation. Another trivial solution is to use XStream, which will serialise your objects into/from XML. You don't need to implement specific interfaces or annotate your objects (by default) and you'll get a readable (in XML terms) serialisation, which can be useful.

One approach would be to use Serialization provided by Java. You need to implement the java.io.Serializable interface and write and read to and from the ObjectOutputStream and ObjectInputStream classes to store and retrieve data respectively.

You need serialization. Read this.

How to restrict raw data to save in text file

I am developing a small application in Java. At certain point i need to save the object of my custom class to a text file for this i override toString() method in my custom class and then use ObjectOutputStream class to save object of my custom class to text file. Now everything works fine i.e my text file contains the text but along with that text it also contians some strange characters or raw data aswell. Following three lines contain major code for that
ObjectOutputStream outputStream = null;
outputStream = new ObjectOutputStream(new FileOutputStream(filename));
outputStream.writeObject(person);//person is the instance of my custom class
Is there any way to restrict that raw data to be saved in my text file?

An ObjectOutputStream serializes objects that you pass to writeObject(). It doesn't write a text version of the object. If you want to write the value returned by toString() to a file, then open a file with something like a FileWriter, get the String by calling the toString() method, and then write it to the FileWriter.

Depending on your needs, you should should maybe have a look at the XML Serialization libraries such as JAXB or XStream.
The solution given above will only save the string representation of your object into a file (which could be what you want) but I guess that if you want to save an object into a file, it's probably to be able to access it afterwards.
Both JAXB and XStream provide methods to serialize/unserialize a Java object in XML. With XStream (maybe with JAXB also, I don't know), you can even serialize/unserialize your object(s) in JSON if you need something more compact.