问题
I am reading a file using bufferedREader ,the file is a text file with lot of text
here is how I am reading it
while(true) //I know the loop is not perfect just ignore it for now, i wanna concentrate on the tracking
{
try
{
br.readLine();
}
catch(IOException e)
{
break;
}
catch (Exception e)
{
break;
}
}
I want to track what percentage of the file I have read so I can use that percentage value in my progress bar like this:
while(true)
{
try
{
br.readLine();
progressBar.setValue(percentageRead);//how do I get percentageRead value dynamically?
}
catch(IOException e)
{
break;
}
catch (Exception e)
{
break;
}
}
回答1:
There are any number ways to achieve this, but you need to keep four things in mind...
- You need to know how much you are reading
- You need to know how much you have read
- You should never performing any action within context of the Event Dispatching Thread that might block it (such as long running loops or blocking I/O)
- You should never modify or change the state of the UI from any thread other then the Event Dispatching Thread
This example simply uses a SwingWorker to read the file in a background thread and uses it's progress functionality to post updates back to the context of the EDT.
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import javax.swing.JFrame;
import javax.swing.JProgressBar;
import javax.swing.SwingWorker;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class ReadFile {
public static void main(String[] args) {
new ReadFile();
}
public ReadFile() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
final JProgressBar pb = new JProgressBar(0, 100);
final ReadFileWorker worker = new ReadFileWorker();
worker.addPropertyChangeListener(new PropertyChangeListener() {
@Override
public void propertyChange(PropertyChangeEvent evt) {
if ("progress".equalsIgnoreCase(evt.getPropertyName())) {
pb.setValue(worker.getProgress());
}
}
});
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new GridBagLayout());
frame.add(pb);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
worker.execute();
}
});
}
public class ReadFileWorker extends SwingWorker<List<String>, String> {
@Override
protected List<String> doInBackground() throws Exception {
List<String> lines = new ArrayList<>(25);
File textFile = new File("Test.txt");
long byteLength = textFile.length();
System.out.println("Reading " + byteLength + " bytes...");
try (InputStream is = new FileInputStream(textFile)) {
byte[] content = new byte[1024];
int bytesRead = -1;
long totalBytes = 0;
String lastText = "";
while ((bytesRead = is.read(content)) != -1) {
totalBytes += bytesRead;
setProgress(Math.round(((float) totalBytes / (float) byteLength) * 100f));
String text = lastText + new String(content);
boolean keepEnd = !text.endsWith("\n");
String[] parts = text.split("\n");
for (int count = 0; count < (keepEnd ? parts.length - 1 : parts.length); count++) {
lines.add(parts[count]);
publish(parts[count]);
}
if (keepEnd) {
lastText = parts[parts.length - 1];
} else {
lastText = "";
}
// This is only here to slow the demonstration down
Thread.sleep(5);
}
System.out.println("Read " + totalBytes + " bytes...");
System.out.println("Read " + lines.size() + " lines...");
} finally {
}
return lines;
}
@Override
protected void done() {
try {
List<String> lines = get();
} catch (InterruptedException | ExecutionException ex) {
ex.printStackTrace();
}
}
}
}
Now, you could incorporate the SwingWorker with one of the other "ProgressInputStream" implementations as well. Take a look at Concurrency in Swing for more details
回答2:
Use a FileInputStream, javax.swing.ProgressMonitorInputStream, InputStreamReader, and a BufferedReader. Then it all happens automatically.
回答3:
Easy
private class myProgressBar{
private int read;
//override constructor and such...
@Override
public int read(byte[] data, int offset, int length) throws IOException
{
int t = super.read(data, offset, length);
if ( t > 0 )
{
read += t;
}
return t;
}
}
then just use standard getter methods. You can get maximum by using myInputStream.availble();
link to relevant source code: http://developer.classpath.org/doc/javax/swing/ProgressMonitorInputStream-source.html
回答4:
As a quick 'hack' you can implement a counting FilterInputStream, and use it in a way that EJP suggests:
public class ProgressInputStream extends FilterInputStream {
private final double maxbytes;
private long current = 0;
public ProgressInputStream(InputStream in, long bytestoexpect) {
super(in);
maxbytes = (double)bytestoexpect;
}
/**
* return a value between 0.0 and 1.0 to represent the progress.
* should do some division-by-zero checking here too.
*/
public double getProgress() {
return current / maxbytes;
}
@Override
public int read() throws IOException {
final int ret = super.read();
if (ret >= 0) {
current++;
}
return ret;
}
@Override
public int read(byte[] b, int off, int len) throws IOException {
final int ret = super.read(b, off, len);
current += ret;
return ret;
}
@Override
public int read(byte[] b) throws IOException {
// TODO Auto-generated method stub
final int ret = super.read(b);
current += ret;
return ret;
}
@Override
public long skip(long n) throws IOException {
final long ret = super.skip(n);
current += ret;
return ret;
}
}
Then, your code can do:
final File infile = new File("path/to/file");
final long insize = infile.length();
final ProgresInputStream pis = new ProgressInputStream(new FileInputStream(infile), insize);
BufferedReader br = new BufferedReader(new InputStreamReader(pis));
String line = null;
try {
while((line = br.readLine()) != null) {
final int pct = (int)(pis.getProgress() * 100.0);
// assume progressbar is final, etc.
SwingUtilities.invokeLater(new Runnable() {
public void run() {
progressBar.setValue(pct);
}
});
}
} catch(IOException e) {
// do proper handling here.....
}
来源：https://stackoverflow.com/questions/19826582/how-do-i-track-reading-of-a-a-file-using-readline-in-java