[SOLVED] write&read a binary file

[tOpach]

I try to write an int array to a binary file and read that binary file.
Could anyone give a sample for writing and reading a binary file please:)

[2potatocakes]

<CODE>
import java.io.DataOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;

/**
* Write some data in binary.
*
* @author Ian F. Darwin, Ian Darwin's Site
* @version $Id: WriteBinary.java,v 1.3 2004/02/08 23:57:29 ian Exp $
*/
public class WriteBinary {
public static void main(String[] argv) throws IOException {
int i = 42;
double d = Math.PI;
String FILENAME = "binary.dat";
DataOutputStream os = new DataOutputStream(new FileOutputStream(
FILENAME));
os.writeInt(i);
os.writeDouble(d);
os.close();
System.out.println("Wrote " + i + ", " + d + " to file " + FILENAME);
}
</CODE>

U can start with that to write in, think I have another for reading.. hang on.. 2 secs

[2potatocakes]

Sorry, this ones better.


import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

class DataIODemo {
public static void main(String args[]) throws IOException {

FileOutputStream fout = new FileOutputStream("Test.dat");
DataOutputStream out = new DataOutputStream(fout);

out.writeDouble(98.6);
out.writeInt(1000);
out.writeBoolean(true);

out.close();

FileInputStream fin = new FileInputStream("Test.dat");
DataInputStream in = new DataInputStream(fin);

double d = in.readDouble();
int i = in.readInt();
boolean b = in.readBoolean();

System.out.println("Here are the values: " + d + " " + i + " " + b);

in.close();
}
}


All the best ;)

[tOpach]

thank you. I add the code to my program. and there is a small problem. I try to write an integer array(with size 1000) to a binary file. I can not append all into file. It only writes last one:(
how can I append ?

kind regards.

[2potatocakes]

post your code up here and let us see what you've done

[tOpach]

I would like to write a kind of data compression. So here is a part of code...

try{
						    FileInputStream fstream1 = new FileInputStream("c:\\Output\\scr.img");
						    
						    DataInputStream in1 = new DataInputStream(fstream1);
						        BufferedReader br1 = new BufferedReader(new InputStreamReader(in1));
						    String strLine1;
						   
						    while ((strLine1 = br1.readLine()) != null)   {
						     //hello
						    	if (z == 0) {
									try {
										BufferedWriter out = new BufferedWriter(
												new FileWriter("c:\\Test.dat",
														true));
										out.write(linebyline_reserve[0] + "\r\n");
										out.close();
									} catch (IOException e1) {
									}
								}
								if (z == 1) {
									try {
										BufferedWriter out = new BufferedWriter(new FileWriter("c:\\Test.dat",true));
										out.write(linebyline_reserve[1] + "\r\n");
										out.close();
									} catch (IOException e1) {
									}
								}
						    //hello
								if (z != 0 && z != 1) {
									for (int d = 0; d < counter; d++) {
										if (strLine1.equals(copy_of_linebyline[d])) {

											FileOutputStream fout = new FileOutputStream("c:\\Test.dat");
											DataOutputStream out = new DataOutputStream(fout);
											out.writeInt(map[d]);
										
											out.writeBoolean(true);

											out.close();

										}
									}
								}
								z++;	
						    }
						    //Close the input stream
						    in1.close();
						    }catch (Exception e1){//Catch exception if any
						      System.err.println("Error: " + e1.getMessage());
						    }

Here, I have 2 arrays. one is integer and other one is string.It is easy to append 2 of them into a text file but I could not manage to do it with binary file.

[tOpach]

I think problem is loop. I mean when I put a loop here

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

class DataIODemo {
public static void main(String args[]) throws IOException {
for(int i=0; i<20; i++){
FileOutputStream fout = new FileOutputStream("Test.dat");
DataOutputStream out = new DataOutputStream(fout);

out.writeDouble(98.6);
out.writeInt(1000);
out.writeBoolean(true);

out.close();
}
}
}

In this case, it overwrites. How can I fix it?

kind regards.

[CJSLMAN]

Because your closing the DataOutputStreamit in the for loop... take the close() method out of the loop and place it after the loop.

Luck,
CJSL

[tOpach]

Thank you it works. I would like to ask one more question. Could you tell me why it works when I call BufferedWriter in a loop and it does not work when I call DataOutputStream. I mean I call .close() with BufferedWriter in a loop and it works.But not with DataOutputStream.

footnot: could you post related links please(binary file IO).


kind regards.

[CJSLMAN]

Actually, you bring up a good point (and I hadn't noticed it). The following:

FileOutputStream fout = new FileOutputStream("Test.dat");
DataOutputStream out = new DataOutputStream(fout);

.. shouldn't be in the loop. They should before the loop (you don't have to create them everytime the program loops)... so it should look something like:

[COLOR="Blue"]FileOutputStream fout = new FileOutputStream("Test.dat");
DataOutputStream out = new DataOutputStream(fout);[/COLOR]
for(int i=0; i<20; i++){
   out.writeDouble(98.6);
   out.writeInt(1000);
    out.writeBoolean(true);
}
[COLOR="blue"]out.close();[/COLOR]

Luck,
CJSL