I'd like to show my Console's output in a text file.
public static void main(String [ ] args){
DataFilter df = new DataFilter();
df.displayCategorizedList();
PrintStream out;
try {
out = new PrintStream(new FileOutputStream("C:\\test1.txt", true));
System.setOut(out);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
I get my result correctly on the screen but not result in the textfile ?
the test file is genereted but it is empty??
You should print to "console" after you have set the system output stream into a file.
DataFilter df = new DataFilter();
PrintStream out;
try {
out = new PrintStream(new FileOutputStream("C:\\test1.txt", true));
System.setOut(out);
df.displayCategorizedList();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (out != null)
out.close();
}
Also use a finally block to always close the stream otherwise data might not be flushed to the file.
I would suggest the following approach:
public static void main(String [ ] args){
DataFilter df = new DataFilter();
try (PrintStream out = new PrintStream(new FileOutputStream("d:\\file.txt", true))) {
System.setOut(out);
df.displayCategorizedList();
} catch (FileNotFoundException e) {
System.err.println(String.format("An error %s occurred!", e.getMessage()));
}
}
This is using the JDK 7 try-with-resources feature - meaning that it deals with exceptions (like FileNotFoundException) that you have and it also closes the resources (instead of the finally block).
If you cannot use JDK 7, use one of the approaches suggested in the other responses.
Related
I found something wrong when I write the Properties file by using FileOutputStream.
public synchronized static void setProperties(String file,String Properties,String value)
{
try {
FileInputStream is = new FileInputStream(file);
Properties proper = new Properties();
proper.load(is);
proper.setProperty(Properties.toUpperCase(), value);
is.close();
FileOutputStream os = new FileOutputStream(file);
proper.store(os,"Update the file:"+Properties);
os.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
Look at the two lines below:
FileOutputStream os = new FileOutputStream(file);
proper.store(os,"Update the file:"+Properties);
When the first line executed, the file will be empty, until the second line execute finished. Now, I assume the second line will execute within 3 seconds. During this period, the program crashed or another reason lead to the file to be unsuccessfully written. I will get an empty Properties file when I'm running my program next time. Anyone can tell me how to prevent this kind of situation to occur?
I changed my program like below, Seems it more better than before. At least I won't get a empty properties file, Thanks all guys.
public synchronized static void setProperties(String file,String Properties,String value)
{
try {
FileInputStream is = new FileInputStream(file);
Properties proper = new Properties();
proper.load(is);
proper.setProperty(Properties.toUpperCase(), value);
is.close();
proper.store(new FileOutputStream(file+".tmp"),"Update the file:"+Properties); //Prevent empty file
File old = new File(file);
File tmp = new File(file+".tmp");
if(tmp.exists() && tmp.length()>0)
{
old.renameTo(new File(file+".old"));
tmp.renameTo(new File(file));
}
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
How to copy the contents of a print statement of a Java program to a text file using Print Stream?
I use the following code to do that from some time now. It works fine. There might be a better way.
PrintStream ps = new PrintStream("\file.txt");
PrintStream orig = System.out;
System.setOut(ps);
//TODO: stuff with System.out.println("some output");
System.setOut(orig);
ps.close();
Consult this answer for better clarification redirect to file
public static void main(String[] args) {
try {
System.setOut(new PrintStream(new File("d:/output.txt")));
System.out.println("StackOverflow");
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
I'm a moderately-experienced C++ guy slowly learning Java. I'm writing a program which needs to do the following:
Create a simple text file, default directory is fine
As the program runs, periodically write one line of data to the file. Depending on a number of factors, the program may write to the file once or a million times. There is no way of knowing which write will be the last.
I've been researching different ways to do this, and this is the working code I've come up with. There are two files, "PeteProgram.java" and "PeteFileMgr.java" :
/*
"PeteProgram.java"
*/
import java.io.*;
import java.lang.String;
public class PeteProgram {
public static void main(String[] args) throws IOException {
String PeteFilename="MyRecordsFile.txt";
Writer writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(PeteFilename), "utf-8"));
PeteFileMgr MyPeteFileMgr = new PeteFileMgr(writer);
MyPeteFileMgr.AddThisString(writer, "Add this line #1\n");
MyPeteFileMgr.AddThisString(writer, "Add this line #2\n");
MyPeteFileMgr.AddThisString(writer, "Add this line #3\n");
}
}
//=====================================================================================================
//=====================================================================================================
/*
"PeteFileMgr.java"
*/
import java.io.*;
public class PeteFileMgr {
public PeteFileMgr(Writer writer) {
try {
writer.write("File created!");
} catch (IOException ex) {
// report
} finally {
try {writer.close();} catch (Exception ex) {}
}
}
void AddThisString(Writer writer, String AddThis) {
try {
writer.append(AddThis);
} catch (IOException ex) {
// report
} finally {
try {writer.close();} catch (Exception ex) {}
}
}
}
The initial creation of the file works just fine. However, the to-be-added lines are not written into the file. Because the program compiles and runs with no errors, I assume the program tries to write the added lines, fails, and throws an exception. (Unfortunately, I am working with a primitive compiler/debugger and can't see if this is the case.)
Does anyone spot my mistake?
Many thanks!
-P
That's because you're not flushing the Writer. You should call flush from time to time. Also, you should close your Writer at the end of your app, not after writing content into it. close method automatically flushes the contents of the writer.
So, this is how your code should look like:
public class PeteProgram {
public static void main(String[] args) {
String peteFilename = "MyRecordsFile.txt";
//here's when the physical file is created
Writer writer = null;
try {
writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(peteFilename), "utf-8"));
PeteFileMgr peteFileMgr = new PeteFileMgr(writer);
peteFileMgr.addThisString(writer, "Add this line #1\n");
peteFileMgr.addThisString(writer, "Add this line #2\n");
peteFileMgr.addThisString(writer, "Add this line #3\n");
} catch (IOException e) {
//handle the exception
//basic handling
e.printStacktrace();
} finally {
//this is a must!
try { writer.close(); } catch(IOException silent) { }
}
}
}
public class PeteFileMgr {
public PeteFileMgr(Writer writer) {
try {
//this method is not creating the physical file
writer.write("File created!");
} catch (IOException ex) {
// report
} finally {
//remove this call to close
//try {writer.close();} catch (Exception ex) {}
}
}
public void addThisString(Writer writer, String addThis) {
try {
writer.append(addThis);
} catch (IOException ex) {
// report
} finally {
//remove this call to close
//try {writer.close();} catch (Exception ex) {}
}
}
}
Or if using Java 7 or superior using the try-with-resources:
public class PeteProgram {
public static void main(String[] args) {
String peteFilename = "MyRecordsFile.txt";
//here's when the physical file is created
try (Writer writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(peteFilename), "utf-8"))) {
PeteFileMgr peteFileMgr = new PeteFileMgr(writer);
peteFileMgr.addThisString(writer, "Add this line #1\n");
peteFileMgr.addThisString(writer, "Add this line #2\n");
peteFileMgr.addThisString(writer, "Add this line #3\n");
} catch (IOException e) {
//handle the exception
//basic handling
e.printStacktrace();
}
}
}
I have a program that needs to load data at launch. The data comes from a serialized object. I have a method loadData(), which is called upon construction of the Data class. Sometimes, (I.e. after a loss of saveData, or on first program launch on a new system), the file can be empty. (The file will exist though, the method ensures that).
When I try to run the program, I recieve an EOFException. So, in the method, I try to catch it, and just print a line to the console explaining what happened and return to the caller of the method. (so, upon return, the program will think loadData() is complete and has returned. However, it still crashes throwing the exception without printing a line to the console or anything. It is like it is totally ignoring the catch I have in place.
CODE:
protected void loadData()
{
// Gets/creates file object.
saveFileObject = new File("savedata.ser");
if(!saveFileObject.exists())
{
try
{
saveFileObject.createNewFile();
}
catch(IOException e)
{
System.out.println("Uh oh...");
e.printStackTrace();
}
}
// Create file input stream
try
{
fileIn = new FileInputStream(saveFileObject);
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
// Create object input stream
try
{
inputStream = new ObjectInputStream(fileIn);
}
catch(IOException e)
{
e.printStackTrace();
}
// Try to deserialize
try
{
parts = (ArrayList<Part>)inputStream.readObject();
}
catch(EOFException e)
{
System.out.println("EOFException thrown! Attempting to recover!");
return;
}
catch(ClassNotFoundException e)
{
e.printStackTrace();
}
catch(IOException e)
{
e.printStackTrace();
}
// close input stream
try
{
inputStream.close();
}
catch(IOException e)
{
e.printStackTrace();
}
}
Any help please?
Try writing your code like :
protected void loadData() {
// Gets/creates file object.
saveFileObject = new File("savedata.ser");
try {
if (!saveFileObject.exists()) {
saveFileObject.createNewFile();
}
// Create file input stream
fileIn = new FileInputStream(saveFileObject);
// Create object input stream
inputStream = new ObjectInputStream(fileIn);
// Try to deserialize
parts = (ArrayList<Part>) inputStream.readObject();
// close input stream
inputStream.close();
} catch (EOFException e) {
System.out.println("EOFException thrown! Attempting to recover!");
} catch (IOException e) {
System.out.println("Uh oh...");
e.printStackTrace();
}
}
Also note that EOFException is a sub-class of IOException
How about making one try and then making catches respectively like here?
I am trying to telnet to a server, run a command and put the output of that command in a file.
I can get the command in the file but not the result of this command.
I cannot see my output on my console either, so I assumed it run but I am not sure.
Does anybody have any idea?
public final static void main(String[] args) throws IOException, InterruptedException
{
FileOutputStream fout = null;
try
{
fout = new FileOutputStream ("spyfile.log");
}
catch (IOException e)
{
System.err.println(
"Exception while opening the spy file: "
+ e.getMessage());
}
TelnetClient telnet;
telnet = new TelnetClient();
try
{
telnet.connect("myserver", 23);
}
catch (IOException e)
{
e.printStackTrace();
System.exit(1);
}
telnet.registerSpyStream(fout);
PrintStream out = new PrintStream( telnet.getOutputStream() );
out.println( "mycommand" );
try
{
telnet.disconnect();
}
catch (IOException e)
{
e.printStackTrace();
System.exit(1);
}
fout.close();
System.exit(0);
}
I am not sure what is TelneClient, if this is Commons Net class, then you are missing the part that actually reads data exchanged during telnet session. Please run this example and see how it works, once you get it you'll be able to cut it to your needs.