java.io question...

I am trying to write some information out to a file.  The contents I want to write out are ints and Strings.  I actually want to write out 5 ints, 1 String, then 5 more ints and 1 String, and I will have to repeat this sequence a number of times.  I want to write them in that order also, because when I read them out, I want to read them in that order.  So I want to know what is the best way to write these values out and then what is the best way to read them back in?
cupOjavaAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

imladrisCommented:
Best is a relative concept of course. It depends on the criteria you use to measure. However, if we assume ease of development and portability your best bet is to use the DataInputStream and the DataOutputStream. To write you would do something like:

DataOutputStream do=new DataOutputStream(new FileOutputStream("filename"));
do.writeInt(i);
do.writeByte(s.length());
do.writeChars(String s);

to read:

DataInputStream di=new DataInputStream(new FileInputStream("filename"));
i=do.readInt();
l=do.readByte();
StringBuffer sb=new StringBuffer();
for(s=0; s<l; ++s)sb.append(do.readChar());
String s=sb.toString();

0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
imladrisCommented:
The extra bits w.r.t. the String are because DataInputStream and -OutputStream don't provide methods for writing or reading Strings.

Note also that, as indicated with the FileInputStream and FileOutputStream, the stream classes can be cascaded together very easily. The DataOutputStream could just as easily have be plugged into a ByteArrayOutputStream or a BufferedOutputStream (which in turn might have been plugged into a FileOutputStream).
Therefore, if you find a Stream method that's better suited to your purposes, it is easy to add or substitute it.

0
imladrisCommented:
Sorry, all the do's in the read example should be di.
0
Cloud Class® Course: CompTIA Cloud+

The CompTIA Cloud+ Basic training course will teach you about cloud concepts and models, data storage, networking, and network infrastructure.

cupOjavaAuthor Commented:
How come you have to writeByte() and then writeChar()?  Is that writing excess data?
0
cupOjavaAuthor Commented:
Would your suggestion work ok if the data in the file was formatted as follows:

30170160Test1100016Testing

Is the compiler smart enough to know that 30, 17, 0, 16, 0 are five different ints?
0
imladrisCommented:
Yes, it is writing some extra data. As pointed out, that is because the DataOutputStream does not natively support the writing of strings. So I suggest compensating for that by, effectively, writing a series of characters.

No, this mechanism will probably not work for the data you describe (30170160Test1100016Testing). The solution I proposed depends on the DataOutputStream creating the file. The DataOutputStream specifically commits to writing out Java primitives in a portable way. However it notes that it will write them out in binary, not ASCII format. I thought this would work since your question indicated that you wished to write data, then read it.

Outputting ASCII data can be done with a PrintStream. This is its purpose in life. Reading ASCII data is more complicated. Certainly I know of no method whatsoever (in any language) of processing the undelimited input you are referencing, unless the number of characters for each field were known in advance. (Is the first number 30 or 301? If the first is 30, is the second 1, 17, or 170?). I don't know what you're requirements are for the file. If the fields can have known lengths you can read the right number of bytes into a String and convert as needed. If you have delimiters (spaces, commas, whatever) you can use a StreamTokenizer to feed back the elements one at a time.

Let me know if there is some specific additional information I could give that would help.


0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Java

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.