Develop Reference

How do you append to the end of a gzipped file in Java?

Here is what I've tried
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;
public class GZIPCompression {
public static void main(String[] args) throws IOException {
File file = new File("gziptest.zip");
try ( OutputStream os = new GZIPOutputStream(new FileOutputStream(file, true))) {
os.write("test".getBytes());
}
try ( GZIPInputStream inStream = new GZIPInputStream(new FileInputStream(file))) {
while (inStream.available() > 0) {
System.out.print((char) inStream.read());
}
}
}
}
Based on what I've read, this should append "test" to the end of gziptest.zip, but when I run the code, the file doesn't get modified at all. The strange thing is that if I change FileOutputStream(file, true) to FileOutputStream(file, false), the file does get modified, but its original contents are overriden which is of course not what I want.
I am using JDK 14.0.1.

A couple of things here.
Zip and GZip are different.. If you are doing a gzip test, your file should have the extension .gz, not .zip
To properly append "test" to the end of the gzip data, you should first use a GZIPInputStream to read in from the file, then tack "test" onto the uncompressed text, and then send it back out through GZipOutputStream

Not able read json file loacted in app's resource folder on azure

I have spring boot app. I am trying to read json file which is located in my resource folder (using class loader). I have deployed my app on azure its giving me error no such file exist and when i print path it is giving me null.

I tried to create a simple Maven project to fix your issue.
My source code structure is like below.
simpleMavenProj
|-src/main/java/Hello.java
|-src/main/resources/hello.json
The content of Hello.java is as below.
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
public class Hello {
public static void main(String[] args) throws IOException {
InputStream resourceInputStream = null;
URL resourceURL = Hello.class.getClassLoader().getResource("resources/hello.json");
if(resourceURL == null) {
System.out.println("Get the InputStream of hello.json in IDE");
resourceInputStream = new FileInputStream(Hello.class.getClassLoader().getResource("").getPath()+"../../src/main/resources/hello.json");
} else {
System.out.println("Get the InputStream of hello.json from runnable jar");
resourceInputStream = Hello.class.getClassLoader().getResourceAsStream("resources/hello.json");
}
System.out.println();
StringBuilder builder = new StringBuilder();
BufferedReader br = new BufferedReader(new InputStreamReader(resourceInputStream));
String line = null;
while((line = br.readLine()) != null) {
builder.append(line+"\n");
}
br.close();
System.out.println(builder.toString());
}
}
And hello.json:
{
"hello":"world"
}
If you are developing in an IDE, run the code and the result is:
Get the InputStream of hello.json in IDE
{
"hello":"world"
}
Else for generating a runable jar file, then to run the jar file via java -jar simpleMavenProj.jar and the result is:
Get the InputStream of hello.json from runnable jar
{
"hello":"world"
}
Hope it helps. Any concern, please feel free to let me know.

i get an error when i run this code

package demo;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.OutputStream;
import org.apache.poi.openxml4j.opc.*;
import org.apache.poi.xwpf.converter.pdf.PdfConverter;
import org.apache.poi.xwpf.converter.pdf.PdfOptions;
import org.apache.poi.xwpf.usermodel.XWPFDocument;
public class DocxToPdf {
public static void main(String[] args){
try
{
String inputFile = "F:\\MY WORK\\CollectionPractice\\WebContent\\APCR1.docx";
String outputFile = "F:\\MY WORK\\CollectionPractice\\WebContent\\APCR1.pdf";
System.out.println("inputFile:" + inputFile + ",outputFile:" + outputFile);
FileInputStream in = new FileInputStream(inputFile);
XWPFDocument document = new XWPFDocument(in);
File outFile = new File(outputFile);
OutputStream out = new FileOutputStream(outFile);
PdfOptions options = null;
PdfConverter.getInstance().convert(document, out, options);
} catch (Exception e) {
e.printStackTrace();
}
}
}
when i run this code an error occur like these and i have used following jar files also.
error:
java.lang.NoSuchMethodError: org.apache.poi.POIXMLDocumentPart.getPackageRelationship()Lorg/apache/poi/openxml4j/opc/PackageRelationship;
jars:
List of jar files

You likely have jar-versions of POI mixed up. The error indicates that the class that was loaded did not have a method that the calling class saw during compilation, so you have a different version of POI in your classpath.
See "Component Map" at https://poi.apache.org/overview.html for the different components that are included and which jars they end up, make sure you only have one of these jars in your classpath, not multiple different versions.

I want to play a sound in Java and it doesn`t work

Hello I want to make an alarm clock and now I`m at the part at makeing the sound play....I wrote this
package audio;
import sun.audio.*;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import sun.audio.AudioPlayer;
import sun.audio.AudioStream;
public class Audio {
public static void main(String[] args) {
InputStream in;
try{
in = new FileInputStream(new File("‪sw.wav"));
AudioStream audio = new AudioStream(in);
AudioPlayer.player.start(audio);
}
catch(Exception e){}
}
}
And it doesn`t play the sound It doesnt give me an error it doesnt do nothing
I also put the direct pathway in a folder C:\...etc

try this: move the audio file to the source folder, then modify the path of the File in the form: new File("‪./sw.wav") and then do something helpful with the exception...
public static void main(String[] args) {
InputStream in;
try{
in = new FileInputStream(new File("‪./sw.wav"));
AudioStream audio = new AudioStream(in);
AudioPlayer.player.start(audio);
}
catch(Exception e){
//print some helpfull info from the stack trace
}
}

The problem in defining the path of FileInputStream you should provide the full path of your audio file and seperate it with double slashes \\:
in = new FileInputStream("C:\\Users\\serban\\Documents\\wav sound\\sw.wav");
Or instead you can move the audio file to the source folder of your java program and then put:
in = new FileInputStream("sw.wav");

Why am I getting a NullPointerException when trying to read a file?

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.