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How to decrypt .dat file with (possibly) java code?

I have a .dat file downloaded from a game, which appears to have some Java code or values in it, along with other illegible text. Here's some of the content:
My question is, is there any way I can decode this file? Or, how can I work out which encryption algorithm it uses so I can search more accurately on how to decrypt it?

The solution from #user207421 worked perfectly, i ended up using this code to get the file info:
public static void main(String[] args) {
try {
FileInputStream fileInputStream = new FileInputStream("./file.dat");
ObjectInputStream inputStream = new ObjectInputStream(fileInputStream);
try {
System.out.println(inputStream.readObject());
} catch (Exception e) {
e.printStackTrace();
}
} catch (IOException e) {
e.printStackTrace();
}
}

How to place a file for jar and read it with FileInputStream

This is the code
public static void readCharacters() {
try (FileInputStream fi = new FileInputStream("main/characters.dat"); ObjectInputStream os = new ObjectInputStream(fi)) {
characterList = (LinkedList<Character>) os.readObject();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
This is the structure:
And this is the Error
java.io.FileNotFoundException: main\characters.dat (The system cannot find the path specified)
What I want is to include the characters.dat file in my jar, and be able to read and write it while the program runs. Is there a different way to write the path? or to put the .dat file in a different position.
Also the writing method:
public static void writeCharacters() {
try (FileOutputStream fs = new FileOutputStream("main/characters.dat"); ObjectOutputStream os = new ObjectOutputStream(fs)) {
System.out.println("Writing Characters...");
os.writeObject(characterList);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}

You can't. You can do one or the other. JAR files are not file systems, and their entries are not files. You can read it with an input stream:
InputStream in = this.getClass().getResourceAsStream("/main/characters.dat");
Check it for null before proceeding.

The jar is for read-only resources. You can use it for the initial file, as a kind of template.
Path path = Paths.get(System.getProperty("user.home") + "/myapp/chars.dat");
Files.mkdirs(path.getParentPath());
if (!Files.exists()) {
try (InputStream in =
Controller.class.getResourceAsStream("/main/characters.dat")) {
Files.copy(in, path);
}
}
The above copies the initial.dat resource from the jar to the user's home "myapp" directory, which is a common solution.
System.getProperty("user.dir") would the running directory. One can also take the jar's path:
URL url = Controller.class.getResource("/main/characters.dat");
String s = url.toExternalForm(); // "jar:file:/.... /xxx.jar!/main/characters.dat"
From that you can also construct the jar's directory. Mind to check Windows, Linux, spaces and such.
URL url = Controller.class.getProtectionDomain().getCodeSource().getLocation();
The solution above risks a NullPointerException, and works a bit differenly running inside the IDE or stand-alone.

Important note:
When using getResourceAsStream, you must start your path by slash /, this specifies the root of your jar, .getResourceAsStream("/file.txt");
In my case my file was a function argument, String filename, I had to do it like this:
InputStream in = this.getClass().getResourceAsStream("/" + filename);

OutputStreamWriter contains a path separator

Today i tested "files" instead of a normal path.
Here is my code:
File path=new File(getFilesDir(),"uf");
File test = new File(path.getAbsolutePath(),"test.txt");
if(!path.exists()){
path.mkdir();
}
if(!test.isFile()){
try {
test.createNewFile();
} catch (IOException e) {
//TODO in errorlog -> filecreation
e.printStackTrace();
}
}else{
try {
OutputStreamWriter mywriter = new OutputStreamWriter(openFileOutput(test.getAbsolutePath().toString(),Context.M ODE_PRIVATE));
mywriter.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
In the error code comes everytime: illegal Arguments: contains a path seperator!
Thank you for your help in advance

Maybe add more info about your error. But...
This error is about that you are trying to full path (include you subdirectories) to access to private data area.
Solution is use FileOutputStream, more here. And use
new File(YOUR_FILE)
to create your file.
Keep on mind that you should call method mkDirs() to create all necessary directories and subdirectories. More about mkDirs() here
Note: There is also method mkDir(), here is doc. This one will create a single directory.

Java Android working with InputStream and File

Well, first of all, I'm just learning and don't quite understand what I'm doing.
What I want is to create an Excel file in memory and then it would be possible to send it with ActionBarSherlock's ShareActionProvider to mail for example.
But I got exeption :
11-24 18:45:52.112: W/System.err(22073): java.io.FileNotFoundException: /Competition.xls: open failed: EROFS (Read-only file system)
As I searched for the answer on the web - it's the problem of file being created in the system area which is read-only. But I want to create it in memory.. Somehow. Once again, I don't really understand well how it works - the way I see it - I create .xls file somewhere in the memory. So the explanation would be helpful.
So, here's the code :
private void createFileTosend() {
InputStream inputStream = null;
FileOutputStream outputStream = null;
try {
File toSend=null;
try {
toSend = getFile();
} catch (WriteException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
inputStream = new BufferedInputStream(new FileInputStream(toSend));
outputStream = openFileOutput("Competition.xls",
Context.MODE_WORLD_READABLE | Context.MODE_APPEND);
byte[] buffer = new byte[1024];
int length = 0;
try {
while ((length = inputStream.read(buffer)) > 0){
outputStream.write(buffer, 0, length);
}
} catch (IOException ioe) {
/* ignore */
}
} catch (FileNotFoundException fnfe) {
/* ignore */
} finally {
try {
inputStream.close();
} catch (IOException ioe) {
/* ignore */
}
try {
outputStream.close();
} catch (IOException ioe) {
/* ignore */
}
}
}
public File getFile() throws IOException, WriteException{
File file=new File("Competition.xls");
WritableWorkbook workbook = Workbook.createWorkbook(file);
//then goes creation of Excel 's xls file which is not important for the question
workbook.write();
workbook.close();
return file;
}
Once again, don't downvote me, please, I'm just learning

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
Ass per the error log you post, i guess you didn't read it carefully. IT is saying read only file system. You need to put the above permission ATLEAST in your android manifest.
Do this much and see if there is any more error or not

I have a doubt may be wrong
outputStream = openFileOutput("Competition.xls",
Context.MODE_WORLD_READABLE | Context.MODE_APPEND);
you are using Context.MODE_WORLD_READABLE its readable, so how can you access it in write mode later. Is it right?
Check this link
Use the http://developer.android.com/guide/topics/data/data-storage.html to clear your doubt about file creation

Why do I get FileNotFoundException when I create and try to write to file on Android emulator?

First off, I am not trying to write to the SDCard. I want to write some information to a file that persists between uses of the app. It is essentially a file to hold favorites of the particular user. Here is what the code looks like:
try {
File file = new File("favorites.txt");
if (file.exists()) {
Log.d(TAG, "File does exist.");
fis = new FileInputStream(file);
br = new BufferedReader(new InputStreamReader(fis));
}
else {
Log.d(TAG, "File does not exist.");
return favDests;
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
When running this code, we always get the "File does not exist." message in our DDMS log.
We have also tried the following code to no avail:
try {
File file = new File(GoLincoln.FAV_DEST_FILE);
fis = new FileInputStream(file);
br = new BufferedReader(new InputStreamReader(fis));
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
It is this second portion of code that results in the FileNotFoundException.
I have read multiple tutorials on writing and reading files on Android and I believe I am following them pretty closely, so I am not sure why this code doesn't work successfully. I appreciate any help!

You shouldn't use the File class directly. Use Activity.getCacheDir() to get the cache dir which is specific to your application. Then use new File(cachedir, "filename.tmp") to create the file.

Preferences and SQLLite will both allow you to have persistent data without managing your own files.
To use shared preferences you grab it from your context, then you edit the values like so
mySharedPreferences = context.getSharedPreferences("DatabaseNameWhateverYouWant", 0);
mySharedPreferences.getEditor().putString("MyPreferenceName", "Value").commit();
To get a preference out
mySharedPreferences.getString("MyPreferenceName", "DefaultValue");
This is really the simplest way to do basic preferences, much easier then doing a file. More then strings are supported, most basic data types are available to be added to the Preferences class.