trouble with Runtime.exec()

[Jason Crest]

i have a directory full of files that needs to be deleted every time my jsp is called so i am using is Runtime.exec() to do it

i am trying to do it as follows

Process p = Runtime.getRuntime().exec("del TEMP_FILES\*.*");

it works when i type it into the dos terminal, but it doesnt work from the jsp.

maybe i just suck at dos or something, lol

drop me a line

thanks

[Jean-Francois Briere]

Why not simply doing:

File[] fileArray = new File("TEMP_FILES").listFiles();
for (int i = 0; i < fileArray.length; i++)
    fileArray[i].delete();

[William Brogden]

1. your statement

Process p = Runtime.getRuntime().exec("del TEMP_FILES\*.*");  

depends on the "current" directory to work correctly. In servlet/jsp you have no way to be sure what directory that is.
2. As I recall, del is a system command, not an executable program
3. What happens if one user is in the middle of something using the temp files and a new user enters the system?

Bill

[Jason Crest]

you make a good point.

here is what im trying to do, im using the JFreeChart api in order to generate graphs of some data that i have. im not sure how to buffer these graphs directly to the browser so the user can view them. right now its set to generate a .png file. hence deleteing the temp images. but if there is a way i can buffer the output to the browser, that would work best i think

here is some code that i have that pertains to generating the jfreechart and .png files.

String title = "";
String xlabel = "something1";
String ylabel = "something2";
XYSeries s1 = new XYSeries( "stuff");
 
while (some condition) {
s1.add( value 1, value 2 );
}

XYSeriesCollection xyCollection1 = new XYSeriesCollection();
xyCollection1.addSeries(s1); 
 
JFreeChart chart = ChartFactory.createScatterPlot(
   title, // chart title
   xlabel, // x axis label
           ylabel, // y axis label
              xyCollection1, // data
                   PlotOrientation.VERTICAL,   // Orientation of range 
               false, // include legend
                   true, // tooltips
               true // urls
               );
 
/*********************
this part creates the image and puts it in whichever directory
it would be great to buffer it straight to the browser at this point
without creating .png files and using an html image tag
**********************/
String dir = "C:\\something.....";
String filename = "some file name";
FileOutputStream Stream = new FileOutputStream( ... );
ChartUtilities.writeChartAsPNG(Stream, chart, 400, 200);
out.println("<IMG SRC=...><BR>");

any suggestions?
thanks
[ June 29, 2004: Message edited by: Jason Crest ]

[William Brogden]

Normally this is done in two steps.
1. record the data that will be used to generate the image in a session and write the HTML page with <img src="theservleturlplussomekey"
2. When the browser does that image request, use the session information to create the PNG into a ByteArrayOutputStream (which creates a byte[] in memory), set the response headers to the content-length and content-type and send the binary image data.

No file involved, everything in memory - automatically GCed.
Bill

[Jason Crest]

im not quite so good at doing the above, however i did try something like

BufferedImage image = chart.createBufferedImage(500,400);
ByteArrayOutputStream stream = new ByteArrayOutputStream();
ChartUtilities.writeBufferedImageAsPNG( stream , image );

however, it doesnt display the image to the browser

[William Brogden]

Some browser are picky about having a content-length header set. Thats the primary reason for writing to an internal buffer first so you can set the length.
resp.setContentType( typeString );
resp.setContentLength( sizeN );
Note those must be called BEFORE you send the byte[] that the ByteArrayOutputStream created.

As I recall, .PDF viewers are also sensitive to getting the right size.
Bill
[ July 01, 2004: Message edited by: William Brogden ]