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Why does the execution order between the printStackTrace() and the other methods appear to be nondeterministic?
(1 answer)
Closed 8 years ago.
I was testing some code to read file available in classpath, but i ended up with some interesting thing related to printStackTrace() method of the Throwable class.
here is the code:
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URISyntaxException;
import java.net.URL;
import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;
public class Main {
public static void main(String[] args) throws IOException, URISyntaxException {
try {
System.out.println("before-test1");
test1(); // will throw exception
System.out.println("after-test1");
} catch (Exception e) {
System.out.println("entering catch-1");
e.printStackTrace();
System.out.println("exiting catch-1");
}
try {
System.out.println("before-test2");
test2();
System.out.println("after-test2");
} catch (Exception e) {
e.printStackTrace();
}
try {
System.out.println("before-test3");
test3();
System.out.println("after-test3");
} catch (Exception e) {
e.printStackTrace();
}
}
private static void test1() throws IOException {
String path = "classpath:/test.txt";
File file = new File(path);
String content = FileUtils.readFileToString(file, "UTF-8");
System.out.println("content = " + content);
}
private static void test2() throws IOException {
String path = "/test.txt";
InputStream in = Main.class.getResourceAsStream(path);
String content = IOUtils.toString(in);
System.out.println("content = " + content);
}
private static void test3() throws IOException, URISyntaxException {
String path = "/test.txt";
URL url = Main.class.getResource(path);
File file = new File(url.toURI());
String content = FileUtils.readFileToString(file, "UTF-8");
System.out.println("content = " + content);
}
}
the content of the test.txt is only one line as per below:
anil bharadia
now the expected output of this program is like below:
before-test1
entering catch-1
java.io.FileNotFoundException: classpath:\test.txt (The filename, directory name, or volume label syntax is incorrect)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at org.apache.commons.io.FileUtils.readFileToString(FileUtils.java:874)
at Main.test1(Main.java:50)
at Main.main(Main.java:16)
exiting catch-1
before-test2
content = anil bharadia
after-test2
before-test3
content = anil bharadia
after-test3
and i have got the same output as above when I ran this class for the first time.
Then after I ran the same class again and i have got the following output:
before-test1
entering catch-1
exiting catch-1
before-test2
content = anil bharadia
after-test2
before-test3
java.io.FileNotFoundException: classpath:\test.txt (The filename, directory name, or volume label syntax is incorrect)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at org.apache.commons.io.FileUtils.readFileToString(FileUtils.java:874)
at Main.test1(Main.java:50)
at Main.main(Main.java:16)
content = anil bharadia
after-test3
in above output the stack trace is printed after the execution of the catch block from which its called and also after the test2()'s execution is over.
so that made me think that printStackTrace() method is asynchronous somehow.
i tried to look into the source of the printStackTrace() and found the following code that didn't help me :
public void printStackTrace(PrintStream s) {
synchronized (s) {
s.println(this);
StackTraceElement[] trace = getOurStackTrace();
for (int i=0; i < trace.length; i++)
s.println("\tat " + trace[i]);
Throwable ourCause = getCause();
if (ourCause != null)
ourCause.printStackTraceAsCause(s, trace);
}
}
I tried to google it but not found any explanation.
And when i tried to run the same class again and again, in many cases i have also found the following output :
java.io.FileNotFoundException: classpath:\test.txt (The filename, directory name, or volume label syntax is incorrect)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at org.apache.commons.io.FileUtils.readFileToString(FileUtils.java:874)
at Main.test1(Main.java:50)
at Main.main(Main.java:16)
before-test1
entering catch-1
exiting catch-1
before-test2
content = anil bharadia
after-test2
before-test3
content = anil bharadia
after-test3
this made me think even more , like how the stack trace got printed before calling the test1() method. that should not be possible.
The stacktrace prints go to a different stream - they're printed to the error stream, rather than the standard out stream. This is why sometimes they'll be displayed in a different order.
System.out.println("after-test3"); write the input to out stream, and printStackTrace() method writes the input to System.err stream
public void printStackTrace() {
printStackTrace(System.err);
}
Error goes to System.err stream.
Normal output goes to System.out stream.
And these streams are written by different threads, so you can also expect different sequence in output if you run again.
To get desired output, you need to change as :
e.printStacktrace(System.out);
This will redirect output to System.out stream.
Related
I'm using Java to create a program that takes in a CSV file and outputs an Arff file. Whenever the program runs it comes up catching the exception that No source has been specified. When I delete the try catch it comes with the following error and I am not sure why,
Exception in thread "main" java.io.IOException: No source has been specified
at weka.core.converters.CSVLoader.getDataSet(CSVLoader.java:867)
at CSVtoArff.Convert(CSVtoArff.java:10)
at CSVtoArff.main(CSVtoArff.java:23)
Below is the code for the program
import weka.core.Instances;
import weka.core.converters.CSVLoader;
import weka.core.converters.ArffSaver;
import java.io.File;
public class CSVtoArff {
public static void Convert(String input, String output) throws Exception {
try {
CSVLoader load = new CSVLoader();
load.setSource(new File(input));
Instances data = load.getDataSet();
ArffSaver save = new ArffSaver();
save.setInstances(data);
save.setFile(new File(output));
save.writeBatch();
System.out.println("File successfully converted");
}
catch (Exception e) {
System.out.println("Does not meet arff standards: " + e.getMessage());
}
}
public static void main(String[] args) throws Exception{
String input = "C:\\Users\\jason\\Desktop\\example.csv";
String output =" C:\\Users\\jason\\Desktop\\example.arff";
Convert(input, output);
}
}
Please try putting the files in C:\temp folder and change it to below and try.
Sometime windows security my be denying access to protected system folders.
Also there is an extra leading space in output file path. I have removed that.
public static void main(String[] args) throws Exception{
String input = "C:/temp/example.csv";
String output ="C:/temp/example.arff";
Convert(input, output);
}
So, I'm working on a program that allows you to import animations in the form of JSON files into Minecraft, and, when working on a completely different part of the program, my import code stopped working.
I'm using eclipse, and this is how my import code looks:
package com.github.sam54123.mc_animation.utils;
import java.io.InputStream;
public class FileHandle
{
public static InputStream inputStreamFromFile(String path)
{
try
{
InputStream inputStream = FileHandle.class.getResourceAsStream(path);
return inputStream;
}
catch(Exception e)
{
e.printStackTrace();
}
return null;
}
}
new file
package com.github.sam54123.mc_animation.utils;
import java.io.File;
import java.io.InputStream;
import java.util.Scanner;
import org.json.JSONObject;
public class JSONUtils
{
public static String getJSONStringFromFile(String path)
{
// Open file
Scanner scanner;
try
{
InputStream in = FileHandle.inputStreamFromFile(path);
scanner = new Scanner(in);
// Get JSON as string without spaces or newlines
String json = scanner.useDelimiter("\\Z").next();
// Close file
scanner.close();
return json;
}
catch(Exception e)
{
System.out.println(e.getStackTrace());
return null;
}
}
public static JSONObject getJSONObjectFromFile(String path)
{
File file = new File(path);
if (!file.exists())
{
System.out.println("Invalid Path");
return null;
}
String string = getJSONStringFromFile(path);
return new JSONObject(string);
}
}
And I proceed to do some more fancy pampering of the file later on. This used to work reliably, until I made this in a completely different and un-related class:
String command = getCommand(object);
if (command != null && command.length() > 0)
{
commands.add(new AnimCommand(command, i));
}
And then it started throwing this error:
[Ljava.lang.StackTraceElement;#7852e922
Exception in thread "main" java.lang.NullPointerException
at java.io.StringReader.<init>(Unknown Source)
at org.json.JSONTokener.<init>(JSONTokener.java:94)
at org.json.JSONObject.<init>(JSONObject.java:406)
at com.github.sam54123.mc_animation.utils.JSONUtils.getJSONObjectFromFile(JSONUtils.java:47)
at com.github.sam54123.mc_animation.system.Animation.<init>(Animation.java:20)
at com.github.sam54123.mc_animation.testing.Tester.main(Tester.java:13)
I've double checked that the file hasn't changed, and I tried deleting that section of code, restarting Eclipse, the whole deal, and nothing seems to fix it. The code is even able to recognize that the file is valid using the File class, but nothing seems to change. Does anyone have some insight on how this might be fixed? Here is the rest of my code: https://github.com/Sam54123/mc-animation/
EDIT
Okay, I've just done some more debugging, and it looks like it's the
return new JSONObject(string);
on line 47 of the second file that's crashing. No idea why, as the risky stuff of reading a file off disk is okay.
EDIT 2
It looks looks like it's failing because
InputStream in = FileHandle.inputStreamFromFile(path);
is returning null, which makes sense because of the try catch statement
InputStream inputStream = FileHandle.class.getResourceAsStream(path);
is in. Why that's failing beats me though, because the validity of the file is verified elsewhere in the code. It also used to work, and I haven't changed anything about the layout of the files.
EDIT 3
Interesting, a couple System.out.printlns reveal the catch is not actually getting activated, and therefore getResourceAsStream() must actually be returning null. I've confirmed this by printing it out before I return it.
I'm trying to create a java.util.List from an existing .txt file, when the list is created and filled with the java.util.String from the .txt file I would like to print it to the console to test if the List is filled. I have tried a lot but I always keep getting the same error.
The layout of the project is as following: Module (QaA), src(WriteTest.java and testfile.txt).
The testfile.txt contains the following:
Sentence one testing
Sentence two testing
Sentence three testing
Sentence four testing
the WriteTest Class:
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
public class WriteTest {
public static void main(String[] args) throws IOException {
Path testPath = Paths.get("src/testfile.txt");
try {
List<String> lines = Files.readAllLines(testPath);
for (String line : lines) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
The following errors are received:
java.nio.file.NoSuchFileException: src\testfile.txt
at sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:79)
at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:97)
at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:102)
at sun.nio.fs.WindowsFileSystemProvider.newByteChannel(WindowsFileSystemProvider.java:230)
at java.nio.file.Files.newByteChannel(Files.java:361)
at java.nio.file.Files.newByteChannel(Files.java:407)
at java.nio.file.spi.FileSystemProvider.newInputStream(FileSystemProvider.java:384)
at java.nio.file.Files.newInputStream(Files.java:152)
at java.nio.file.Files.newBufferedReader(Files.java:2784)
at java.nio.file.Files.readAllLines(Files.java:3202)
at java.nio.file.Files.readAllLines(Files.java:3242)
at WriteTest.main(WriteTest.java:15)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)
I have found another reason why I had loads of errors. The location of my .txt file should not have been within the src. I tried moving it out, parallel to my module, and there it was detectable.
Your code had error on my workspace, I changed the readAllLines as you see below, and added toAbsolutePath for the path
public static void main(String[] args) throws IOException
{
Path testPath = Paths.get("src/testfile.txt").toAbsolutePath();
System.out.println("path:\t" + testPath);
try
{
Charset cs = Charset.defaultCharset();
List<String> lines = Files.readAllLines(testPath, cs);
for (String line : lines)
{
System.out.println(line);
}
}
catch (IOException e)
{
e.printStackTrace();
}
}
Make the changes as below to get the given file path.
Path testPath = Paths.get(System.getProperty("user.dir")+"src/testfile.txt");
my first java program ..
so I'm trying to create a file and store in my pc using java
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
public class createfile {
public static void main(String[] args) throws IOException {
int[] numbers = {1,2,3};
for (int item : numbers) {
String key = "file" + item;
File file = File.createTempFile("c:\\",key,".txt");
Writer writer = new OutputStreamWriter(new FileOutputStream(file));
writer.write("abcdefghijklmnopqrstuvwxyz\n");
writer.write("01234567890112345678901234\n");
writer.write("!##$%^&*()-=[]{};':',.<>/?\n");
writer.write("01234567890112345678901234\n");
writer.write("abcdefghijklmnopqrstuvwxyz\n");
writer.close();
}
return file;
}
}
what am I missing here .. I coudln't figured it out. everything seem to follow along the book.
Thanks
===========update ===========
after I took of
- return file ;
- throws IOException ;
- and change to File file = File.createTempFile(key,".txt",new File("c:\\"));
I still get this error
Exception in thread "main" java.lang.Error: Unresolved compilation problems:
Unhandled exception type IOException
Unhandled exception type FileNotFoundException
Unhandled exception type IOException
Unhandled exception type IOException
Unhandled exception type IOException
Unhandled exception type IOException
Unhandled exception type IOException
Unhandled exception type IOException
you have some mistakes in java syntax:
When you declare method as void (here public static void main(....)) it means that method has no return value - so line "return file;" not needed here.
Use use wrong signature (wrong parameters types in File.createTempFile function.
Possible usages are:
createTempFile(String prefix, String suffix)
createTempFile(String prefix, String suffix, File directory)
For additional information about File class use this link: http://docs.oracle.com/javase/6/docs/api/java/io/File.html
Following possible version of working code:
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
public class createfile
{
public static void main(String[] args) throws IOException
{
int[] numbers = {1,2,3};
for (int item : numbers)
{
String key = "file" + item;
File file = File.createTempFile(key,".txt",new File("c:\\"));
Writer writer = new OutputStreamWriter(new FileOutputStream(file));
writer.write("abcdefghijklmnopqrstuvwxyz\n");
writer.write("01234567890112345678901234\n");
writer.write("!##$%^&*()-=[]{};':',.<>/?\n");
writer.write("01234567890112345678901234\n");
writer.write("abcdefghijklmnopqrstuvwxyz\n");
writer.close();
}
}
}
You can also see another sample how to write text to file: http://www.homeandlearn.co.uk/java/write_to_textfile.html. This link use NetBeans as Java Tool for writing code. I strongly suggest to use some IDE (Eclipse,NetBeans) to write code in java.It will mark your compile mistakes and will suggest corrections.
NetBeans site:https://netbeans.org/
Welcome to Java world
public static void main(String[] args) throws IOException { doesn't return anything, so the return file statement is not required
File.createTempFile either takes String, String, File or String, String so File file = File.createTempFile("c:\\", key, ".txt"); won't compile.
Something like, File file = File.createTempFile(key, ".txt", new File("c:\\")); might be a better idea, but is depended on what you want to achieve.
The JavaDocs state that the prefix must be at least three characters long, so you'll need to pad the key value to meet these requirements.
You MAY find using something like...
File file = new File("C:\\" + key + ".txt");
more managable...
I use this test to convert txt to pdf :
package convert.pdf;
//getResourceAsStream(String name) : Returns an input stream for reading the specified resource.
//toByteArray : Get the contents of an InputStream as a byte[].
import java.io.FileOutputStream;
import java.io.IOException;
import org.apache.commons.io.IOUtils;
import convert.pdf.txt.TextConversion;
public class TestConversion {
private static byte[] readFilesInBytes(String file) throws IOException {
return IOUtils.toByteArray(TestConversion.class.getResourceAsStream(file));
}
private static void writeFilesInBytes(byte[] file, String name) throws IOException {
IOUtils.write(file, new FileOutputStream(name));
}
//just change the extensions and test conversions
public static void main(String args[]) throws IOException {
ConversionToPDF algorithm = new TextConversion();
byte[] file = readFilesInBytes("/convert/pdf/text.txt");
byte[] pdf = algorithm.convertDocument(file);
writeFilesInBytes(pdf, "text.pdf");
}
}
Problem:
Exception in thread "main" java.lang.NullPointerException
at org.apache.commons.io.IOUtils.copyLarge(IOUtils.java:1025)
at org.apache.commons.io.IOUtils.copy(IOUtils.java:999)
at org.apache.commons.io.IOUtils.toByteArray(IOUtils.java:218)
at convert.pdf.TestConversion.readFilesInBytes(TestConversion.java:17)
at convert.pdf.TestConversion.main(TestConversion.java:28)
I use the debugger, and the problem seems to be located here :
private static byte[] readFilesInBytes(String file) throws IOException {
return IOUtils.toByteArray(TestConversion.class.getResourceAsStream(file));
}
What is my problem?
Sounds like the resource probably doesn't exist with that name.
Are you aware that Class.getResourceAsStream() finds a resource relative to that class's package, whereas ClassLoader.getResourceAsStream() doesn't? You can use a leading forward slash in Class.getResourceAsStream() to mimic this, so
Foo.class.getResourceAsStream("/bar.png")
is roughly equivalent to
Foo.class.getClassLoader().getResourceAsStream("bar.png")
Is this actually a file (i.e. a specific file on the normal file system) that you're trying to load? If so, using FileInputStream would be a better bet. Use Class.getResourceAsStream() if it's a resource bundled in a jar file or in the classpath in some other way; use FileInputStream if it's an arbitrary file which could be anywhere in the file system.
EDIT: Another thing to be careful of, which has caused me problems before now - if this has worked on your dev box which happens to be Windows, and is now failing on a production server which happens to be Unix, check the case of the filename. The fact that different file systems handle case-sensitivity differently can be a pain...
Are you checking to see if the file exists before you pass it to readFilesInBytes()? Note that Class.getResourceAsStream() returns null if the file cannot be found. You probably want to do:
private static byte[] readFilesInBytes(String file) throws IOException {
File testFile = new File(file);
if (!testFile.exists()) {
throw new FileNotFoundException("File " + file + " does not exist");
}
return IOUtils.toByteArray(TestConversion.class.getResourceAsStream(file));
}
or better yet:
private static byte[] readFilesInBytes(String file) throws IOException {
InputStream stream = TestConversion.class.getResourceAsStream(file);
if (stream == null) {
throw new FileNotFoundException("readFilesInBytes: File " + file
+ " does not exist");
}
return IOUtils.toByteArray(stream);
}
This class reads a TXT file in the classpath and uses TextConversion to convert to PDF, then save the pdf in the file system.
Here TextConversion code :
package convert.pdf.txt;
//Conversion to PDF from text using iText.
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import convert.pdf.ConversionToPDF;
import convert.pdf.ConvertDocumentException;
import com.lowagie.text.Document;
import com.lowagie.text.DocumentException;
import com.lowagie.text.Font;
import com.lowagie.text.Paragraph;
import com.lowagie.text.pdf.PdfWriter;
public class TextConversion implements ConversionToPDF {
public byte[] convertDocument(byte[] documents) throws ConvertDocumentException {
try {
return this.convertInternal(documents);
} catch (DocumentException e) {
throw new ConvertDocumentException(e);
} catch (IOException e) {
throw new ConvertDocumentException(e);
}
}
private byte[] convertInternal(byte[] documents) throws DocumentException, IOException {
Document document = new Document();
ByteArrayOutputStream pdfResultBytes = new ByteArrayOutputStream();
PdfWriter.getInstance(document, pdfResultBytes);
document.open();
BufferedReader reader = new BufferedReader( new InputStreamReader( new ByteArrayInputStream(documents) ) );
String line = "";
while ((line = reader.readLine()) != null) {
if ("".equals(line.trim())) {
line = "\n"; //white line
}
Font fonteDefault = new Font(Font.COURIER, 10);
Paragraph paragraph = new Paragraph(line, fonteDefault);
document.add(paragraph);
}
reader.close();
document.close();
return pdfResultBytes.toByteArray();
}
}
And here the code to ConversionToPDF :
package convert.pdf;
// Interface implemented by the conversion algorithms.
public interface ConversionToPDF {
public byte[] convertDocument(byte[] documentToConvert) throws ConvertDocumentException;
}
I think the problem come from my file system (devbox on windows and server is Unix).
I will try to modify my classpath.
This problem may be caused by calling methods on test.txt, which can be a folder shortcut. In other words, you're calling a method on a file that doesn't exist, resulting in a NullPointerException.