Develop Reference

How to download a file from the internet using Java

Hi I am trying to write some code in my program so I can grab a file from the internet but it seems that is not working. Can someone give me some advice please ? Here is my code. In this case I try to download an mp3 file from the last.fm website, my code runs perfectly fine but when I open my downloads directory the file is not there. Any idea ?
public class download {
public static void main(String[] args) throws IOException {
String fileName = "Death Grips - Get Got.mp3";
URL link = new URL("http://www.last.fm/music/+free-music-downloads");
InputStream in = new BufferedInputStream(link.openStream());
ByteArrayOutputStream out = new ByteArrayOutputStream();
byte[] buf = new byte[1024];
int n = 0;
while (-1!=(n=in.read(buf)))
{
out.write(buf, 0, n);
}
out.close();
in.close();
byte[] response = out.toByteArray();
FileOutputStream fos = new FileOutputStream(fileName);
fos.write(response);
fos.close();
System.out.println("Finished");
}
}

Every executing program has a current working directory. Often times, it is the directory where the executable lives (if it was launched in a "normal" way).
Since you didn't specify a path (in fileName), the file will be saved with that name in the current working directory.
If you want the file to be saved in your downloads directory, specify the full path. E.g.
String fileName = "C:\\Users\\YOUR_USERNAME\\Downloads\\Death Grips - Get Got.mp3";
Note how I've escaped the backslashes. Also note that there are methods for joining paths in Java. There is a way to get the current working directory in Java.

Create and download CSV file in a Java servlet

I am working on Java ExtJS application in which I need to create and download a CSV file.
On clicking a button I want a CSV file to be downloaded to a client's
machine.
On buttons listener I am calling a servlet using AJAX. There I am
creating a CSV file.
I don't want the CSV file to be saved in the server. I want the file should be created dynamically with a download option. I want the contents of a file to be created as a string and then I will serve the content as file in which it will open as download mode in browser (this I have achieved in other language, but not sure how to achieve it in Java).
Here is my code only to create a CSV file, but I really don't want to create or save CSV file if I can only download the file as CSV.
public String createCSV() {
try {
String filename = "c:\\test.csv";
FileWriter fw = new FileWriter(filename);
fw.append("XXXX");
fw.append(',');
fw.append("YYYY");
fw.append(',');
fw.append("ZZZZ");
fw.append(',');
fw.append("AAAA");
fw.append(',');
fw.append("BBBB");
fw.append('\n');
CSVResult.close();
return "Csv file Successfully created";
} catch(Exception e) {
return e.toString();
}
}
Can any one help me on this.
Thanks

I got the solution and I am posting it below.
public void doGet(HttpServletRequest request, HttpServletResponse response)
{
response.setContentType("text/csv");
response.setHeader("Content-Disposition", "attachment; filename=\"userDirectory.csv\"");
try
{
OutputStream outputStream = response.getOutputStream();
String outputResult = "xxxx, yyyy, zzzz, aaaa, bbbb, ccccc, dddd, eeee, ffff, gggg\n";
outputStream.write(outputResult.getBytes());
outputStream.flush();
outputStream.close();
}
catch(Exception e)
{
System.out.println(e.toString());
}
}
Here we don't need to save / store the file in the server.
Thanks

First of all you need to get the HttpServletResponse object so that you can stream a file into it.
Note : This example is something I Wrote for one of my projects and it works.Works on Java 7.
Assuming you got the HttpServletResponse you can do something like this to stream a file. This way the file will be saved into clients' machine.
public void downloadFile(HttpServletResponse response){
String sourceFile = "c:\\source.csv";
try {
FileInputStream inputStream = new FileInputStream(sourceFile);
String disposition = "attachment; fileName=outputfile.csv";
response.setContentType("text/csv");
response.setHeader("Content-Disposition", disposition);
response.setHeader("content-Length", String.valueOf(stream(inputStream, response.getOutputStream())));
} catch (IOException e) {
logger.error("Error occurred while downloading file {}",e);
}
}
And the stream method should be like this.
private long stream(InputStream input, OutputStream output) throws IOException {
try (ReadableByteChannel inputChannel = Channels.newChannel(input); WritableByteChannel outputChannel = Channels.newChannel(output)) {
ByteBuffer buffer = ByteBuffer.allocate(10240);
long size = 0;
while (inputChannel.read(buffer) != -1) {
buffer.flip();
size += outputChannel.write(buffer);
buffer.clear();
}
return size;
}
}
What this does is, get an inputstream from your source file and write that stream into the outputstream of the HttpServletResponse. This should work since it works perfectly for me. Hope this helps. Sorry for my bad English.

I would like add something to the answer by gaurav. I recently had to implment this functionality in a project of mine and using javascript was out of the question becuase we had to support IE 9. What is the problem with IE 9?
(Export to CSV using jQuery and html), see the second answer in the link.
I needed an easy way to convert a ResultSet of a database query to a string which represent the the same data in CSV format. For that I used http://opencsv.sourceforge.net/ which provided an easy way to get a String ot of the ResultSet, and the rest is as above answer did it.
THe examples in the project soruce folder give good examples.

Program Not Creating File. What is Wrong?

I have tried creating a file, using the code below:
import java.io.File;
public class DeleteEvidence {
public static void main(String[] args) {
File evidence = new File("cookedBooks.txt");
However, the file cookedBooks.txt does not exist anywhere on my computer. I'm pretty new to this, so I'm having problems understanding other threads about similar problems.

You have successfully created an instance of the class File, which is very different from creating actual files in your hard drive.
Instances of the File class are used to refer to files on the disk. You can use them to many things, for instance:
check if files or directories exist;
create/delete/rename files or directories; and
open "streams" to write data into the files.
To create a file in your hard disk and write some data to it, you could use, for instance, FileOutputStream.
public class AnExample {
public static void main(String... args) throws Throwable {
final File file = new File("file.dat");
try (FileOutputStream fos = new FileOutputStream(file);
DataOutputStream out = new DataOutputStream(fos)) {
out.writeInt(42);
}
}
}
Here, fos in an instance of FileOutputStream, which is an OutputStream that writes all bytes written to it to an underlying file on disk.
Then, I create an instance of DataOutputStream around that FileOutputStream: this way, we can write more complex data types than bytes and byte arrays (which is your only possibility using the FileOutputStream directly).
Finally, four bytes of data are written to the file: the four bytes representing the integer 42. Note that, if you open this file on a text editor, you will see garbage, since the code above did not write the characters '4' and '2'.
Another possibility would have been to use an OutputStreamWriter, which would give you an instance of Writer that can be used to write text (non-binary) files:
public class AnExample {
public static void main(String... args) throws Throwable {
final File file = new File("file.txt");
try (FileOutputStream fos = new FileOutputStream(file);
OutputStreamWriter out = new OutputStreamWriter(fos, StandardCharsets.UTF_8)) {
out.write("You can read this with a text editor.");
}
}
}
Here, you can open the file file.txt on a text editor and read the message written to it.

File evidence = new File(path);
evidence.mkdirs();
evidence.createNewFile();

File is an abstract concept of a file which does not have to exist. Simply creating a File object does not actually create a physical object.
You can do this in (at least) two ways.
Write something to the file (reference by the abstract File object)
Calling File#createNewFile
You can also create temporary files using File#createTempFile but I don't think this is what you are trying to achieve.

You have only created an object which can represent a file. This is just in memory though. If you want to access the file you must us ea FileInputStream or a FileOutputStream. Then it will also be created on the drive (in case of the outputstream).
FileOutputStream fo = new FileOutputStream(new File(oFileName));
fo.write("test".getBytes());
fo.close();

This is just ur creating file object by using this object u need to call one method i.e createFile() method..
So use evidence.createNewFile(); if you are creating just file.
else if u want to create file in any specific location then specify your file name
i.e File evidence=new File("path");
In this case if ur specifying any directoty

String path="abc.txt";
File file = new File(path);
if (file.createNewFile()) {
System.out.println("File is created");
}
else {
System.out.println("File is already created");
}
FileWriter fw = new FileWriter(file, true);
string ab="Hello";
fw.write(ab);
fw.write(summary);
fw.close();

java - How do I save an Uploaded Image to my C drive

This is a follow-up to what I was trying to accomplish here https://stackoverflow.com/questions/7313922/uploading-files-ussing-myfaces-tomahawk-jsf-2-0
I've managed to get the image as an UploadedFile Object, but I can't seem to be able to save it to disk. I want to save it locally (in C:\Temp, for example) such that when I run my app, I can upload a file (test.jpg, for example) from my desktop and see it saved on the server (for example, in C:\Temp).
My bean is pretty simple:
import org.apache.myfaces.custom.fileupload.UploadedFile;
public class PatientBB {
private UploadedFile uploadedFile;
public UploadedFile getUploadedFile(){
return this.uploadedFile;
}
.
public void setUploadedFile(UploadedFile uploadedFile){
this.uploadedFile = uploadedFile;
}
.
public String actionSubmitImage(){
//This is th part I need help with. how do I save it in my C?
}
I greatly Appreciate all the help, thank you!

As far as I can tell, according to the javaDoc, you should be able to do
uploadedFile.getInputStream();
and then push the data from that to a FileOutputStream.
Psuedo:
InputStream is = uploadedFile.getInputStream();
byte[] buffer = new byte[uploadedFile.getLength()); //This can be more space-efficient if necessary
is.read(buffer);
File f = new File("C:\\tmp\\" + uploadedFile.getFilename());
f.createNewFile();
FileOutputStream fos = new FileOutputStream(f);
fos.write(buffer);
Does that make sense? Is that what you're looking for?

The uploaded file can be copy to the specified location using java FileUtils API.
File theFile = new File("C:\temp\filename");
eg: FileUtils.copyFile(upload, theFile);

File Delete and Rename in Java

I have the following Java code which will search in an xml for a specific tag and then will add some text to it and save that file. I couldnt find a way to rename the emporary file to the original file. Please suggest.
import java.io.*;
class ModifyXML {
public void readMyFile(String inputLine) throws Exception
{
String record = "";
File outFile = new File("tempFile.tmp");
FileInputStream fis = new FileInputStream("InfectiousDisease.xml");
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
FileOutputStream fos = new FileOutputStream(outFile);
PrintWriter out = new PrintWriter(fos);
while ( (record=br.readLine()) != null )
{
if(record.endsWith("<add-info>"))
{
out.println(" "+"<add-info>");
out.println(" "+inputLine);
}
else
{
out.println(record);
}
}
out.flush();
out.close();
br.close();
//Also we need to delete the original file
//outFile.renameTo(InfectiousDisease.xml);//Not working
}
public static void main (String[] args) {
try
{
ModifyXML f = new ModifyXML();
f.readMyFile("This is infectious disease data");
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
Thanks

First delete the original file and then rename the new file:
File inputFile = new File("InfectiousDisease.xml");
File outFile = new File("tempFile.tmp");
if(inputFile.delete()){
outFile.renameTo(inputFile);
}

A good method to rename files is.
File file = new File("path-here");
file.renameTo(new File("new path here"));

In your code there are several issues.
First your description mentions renameing the original file and adding some text to it. Your code doesn't do that, it opens two files, one for reading and one for writing (with the additional text). That is the right way to do things, as adding text in-place is not really feasible using the techniques you are using.
The second issue is that you are opening a temporary file. Temporary files remove themselves upon closing, so all the work you did adding your text disappears as soon as you close the file.
The third issue is that you are modifying XML files as plain text. This sometimes works as XML files are a subset of plain text files, but there is no indication that you attempted to ensure that the output file was an XML file. Perhaps you know more about your input files than is mentioned, but if you want this to work correctly for 100% of the input cases, you probably want to create a SAX writer that writes out all a SAX reader reads, with the additional information in the correct tag location.

You can use
outFile.renameTo(new File(newFileName));
You have to ensure these files are not open at the time.