Using a Buffer
Dear all ,
I need to transfer files of unknown maximum size into an array of bytes
i',m using this code :
FileInputStream fis =new FileInputStream(oldPath);
byte[] bytes =newbyte[fis.available()];
fis.read(bytes, 0, fis.available());
fis.close();
but on transferring an exe of size 154 MG , i got heap out of memory exception , so how can i improve my code to make use of buffers?
i have no idea how can i do so ?
can anybody help me ?
wishing to find any reply
thanks in advance.
Regards,
D.Roth
[721 byte] By [
d_rotha] at [2007-11-27 2:31:40]
> Dear all ,
> I need to transfer files of unknown maximum size
> into an array of bytes
> ',m using this code :
>
> > FileInputStream fis = new FileInputStream(oldPath);
> byte[] bytes = new byte[fis.available()];
> fis.read(bytes, 0, fis.available());
> fis.close();
>
> but on transferring an exe of size 154 MG , i got
> heap out of memory exception , so how can i improve
> my code to make use of buffers?
> i have no idea how can i do so ?
> can anybody help me ?
> wishing to find any reply
> thanks in advance.
> Regards,
> D.Roth
You try:
File file = new File(oldPath); // figuring oldPath is the file name
byte[] bytes = file.length();
FileInputStream fis = new FileInputStream(file);
int done = fis.read(bytes);
fis.close();
-and-
cmd /c start /min java -Xms128m -Xmx1024m YouClassFileNameHere
... Substituting the numbers you want for Xms and Xmx ?
import java.io.*;
import java.util.*;
/**
* BigFileReader contains two methods to read a file from a file system.
* Two methods are used to illustrate optimized reading abilities
*
* @version 1.0
*/
public class BigFileReader {
/**
* Default constuctor
*/
public BigFileReader(){ }
/**
* Reads a file storing intermediate data into a list. Fast method.
* @param file the file to be read
* @return a file data
*/
public byte[] read2list(String file) throws Exception {
InputStream in = null;
byte[] buf = null; // output buffer
intbufLen = 20000*1024;
try{
in = new BufferedInputStream(new FileInputStream(file));
buf = new byte[bufLen];
byte[] tmp = null;
int len= 0;
List data = new ArrayList(24); // keeps peaces of data
while((len = in.read(buf,0,bufLen)) != -1){
tmp = new byte[len];
System.arraycopy(buf,0,tmp,0,len); // still need to do copy
data.add(tmp);
}
/*
This part os optional. This method could return a List data
for further processing, etc.
*/
len = 0;
if (data.size() == 1) return (byte[]) data.get(0);
for (int i=0;i<data.size();i++) len += ((byte[]) data.get(i)).length;
buf = new byte[len]; // final output buffer
len = 0;
for (int i=0;i<data.size();i++){ // fill with data
tmp = (byte[]) data.get(i);
System.arraycopy(tmp,0,buf,len,tmp.length);
len += tmp.length;
}
}finally{
if (in != null) try{ in.close();}catch (Exception e){}
}
return buf;
}
/**
* Reads a file storing intermediate data into an array.
* @param file the file to be read
* @return a file data
*/
public byte[] read2array(String file) throws Exception {
InputStream in = null;
byte[] out = new byte[0];
try{
in = new BufferedInputStream(new FileInputStream(file));
// the length of a buffer can vary
int bufLen = 20000*1024;
byte[] buf = new byte[bufLen];
byte[] tmp = null;
int len= 0;
while((len = in.read(buf,0,bufLen)) != -1){
// extend array
tmp = new byte[out.length + len];
// copy data
System.arraycopy(out,0,tmp,0,out.length);
System.arraycopy(buf,0,tmp,out.length,len);
out = tmp;
tmp = null;
}
}finally{
// always close the stream
if (in != null) try{ in.close();}catch (Exception e){}
}
return out;
}
/**
* Creates a big file with given name
* @param file the file name
*/
public void createData(String file) throws Exception {
BufferedOutputStream os = new BufferedOutputStream(
new FileOutputStream(file));
byte[] b = new byte[]{0xC,0xA,0xF,0xE,0xB,0xA,0xB,0xE};
intc = 1000000;
for (int i=0;i<c;i++){
os.write(b);
os.flush();
}
}
/**
* Test two different data reading algorithms:
* First, it creates a file, then it reads data using read2list method and,
* finally, it reads data with read2array method.
*/
public static void main(String[] v) throws Exception {
BigFileReader bfr = new BigFileReader();
System.out.println("creating a file...");
bfr.createData("data.dat");
System.out.println("file created");
long t = System.currentTimeMillis();
byte[] b = bfr.read2list("data.dat");
t = System.currentTimeMillis()-t;
System.out.println("read "+(b == null ? 0 : b.length)+
" byte(s) with read2list method in "+t+" ms");
t = System.currentTimeMillis();
b = bfr.read2array("data.dat");
t = System.currentTimeMillis()-t;
System.out.println("read "+(b == null ? 0 : b.length)+
" byte(s) with read2array method in "+t+" ms");
}
}
>
