Develop Reference

Displaying a text file on a webpage

I'm new to coding and have decided to start my learning on Java. I've got NetBeans and have started to create a very basic web application. I'd like to be able to display values from a .txt file onto the webpage, and I've got this code to do so.
<%
BufferedReader in = new BufferedReader(new FileReader("Cats.txt"));
String line;
while((line = in.readLine()) != null)
{
out.println(line);
}
in.close();
%>
My text file is in the same folder as my src folder (As I've seen you need to put the file)
However, whenever I navigate to the web page I get a FileNotFound error. I've tried placing the files path in the FileReader but that gives an error due to the backslashes.
If anyone could help I'd be greatly appreciated

Currently it's looking for the file in the src directory of your application you should just be able move the file there and it should read it. If you would like to direct to a specific path you need to tell the IDE to treat the '\' as a normal slash to do this you need to close it off by using two '\'s instead of one eg:
<%
BufferedReader in = new BufferedReader(new
FileReader("C:\\MYPATH\\MYPATH2\\Cats.txt"));
String line;
while((line = in.readLine()) != null)
{
out.println(line);
}
in.close()
%>

How to load the same JSON file in both an Android app and local unit test?

I have an Android project that displays data from a JSON file. The file is read from the assets directory, following the approach below:
src/main/assets/my_file.json
InputStream is = getResources().getAssets().open(filename);
BufferedReader br = new BufferedReader(new InputStreamReader(is));
// use StringBuilder to get file contents as String
I also have local unit tests which require the same JSON file. In order to avoid the slowness of Instrumentation tests, I am currently loading a duplicate of the file as below:
src/main/resources/my_copy.json
File testData = new File(getClass().getResource(filename).getPath());
InputStream is = new FileInputStream(testData);
// read File as before
Is there an approach that would allow the JSON file to be stored in one location, whilst running the unit tests on a local JVM?

If you're using Robolectric, see this answer.
Note that the "assets" directory is an Android concept, it's different from Java resources. That said, you could also move your JSON file from assets to resources, and use it from both Android and JVM form there like you would in any Java application.

Files in the resource directory can be accessed within Android applications by using ClassLoader#getResourceAsStream(). This returns an InputStream, which can then be used to read the file. This avoids having to duplicate files between resources and the assets directory.
InputStream is = getClass().getClassLoader().getResourceAsStream("my_file.json");
BufferedReader br = new BufferedReader(new InputStreamReader(is));
String line = null;
StringBuilder sb = new StringBuilder();
while ((line = br.readLine()) != null) {
sb.append(line);
}
}
String json = sb.toString();

Getting the newest version (not the cached version) of a text file on a server using java Streams to read

I have a url of a text file and I want to read it:
URL url = new URL("example.com/textfile.txt");
BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
String inpuline = null;
while ((inpuline = in.readLine()) != null) {
System.out.println(inpuline);
}
in.close();
The problem is when I change the Content of textfile.txt, my program does not realize the changes next time it runs.

After you change the txt file, you should verify that your server realized the changes and return the last version of your file. To verify this use a browser. If you didn't get the last version of your file something is wrong with the server. If you need to press Ctrl+F5 it means that the maybe some proxies or your browser cashed the old file.
After all trying the following workarounds may helps:
try {
URL url = new URL("example.com/textfile.txt");
Scanner s = new Scanner(url.openStream());
// read from your scanner
}
catch(IOException ex) {
ex.printStackTrace(); // for now, simply output it.
}
If you got the cached version of your file again, then try to use HttpURLConnection to download the file and write it to a temp file. Then read from that temp file and after that delete that temp file. Maybe downloading the file can force the server to get the newest version of that file. To avoid cached version of your file try this:
// Create a URLConnection object
URLConnection connection = myURL.openConnection();
// Disable caching
connection.setUseCaches(false);
Good Luck.

Making web crawler download multiple web pages locally

I would like my web crawler to download all the browsed URL's locally. At the minute it will download every site it comes to but then overwrite the local file in each website visited. The crawler start at www.bbc.co.uk, downloads that file and then when it hits another it overwrites that file with the next URL. How can I make it download them in to single files so I have a collection at the end? I have this code below but I dont know where to go from here. Any advice would be great. The URL inside the brackets (URL) is a string which is used to manipulate all the browsed webpages.
URL url = new URL(URL);
BufferedWriter writer;
try (BufferedReader reader = new BufferedReader
(new InputStreamReader(url.openStream()))) {
writer = new BufferedWriter
(new FileWriter("c:/temp/data.html", true));
String line;
while ((line = reader.readLine()) != null) {
//System.out.println(line);
writer.write(line);
writer.newLine();
}
}
writer.close();

You need to give to your files a unique name.
You can save them in different folders (one root directory for each web site).
Or you can give them a unique name (using a counter for example).

BufferedReader gives weird behaviour on different Android versions

I am trying to open an existing file, and process it, and save it somewhere else in Android.
File in = new File("/sdcard/a.pdf"); // This file exists in the location and has been obtained by using getExternalStorage()
FileInputStream fis = new FileInputStream(in);
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
header = br.readLine(); // this gives first line in android 2.3.3 but gives null in android 2.3.6
Executing the above code in Android 2.3.3 gives me the header while executing it in Android 2.3.6 gives "null" in the header.
What may be the problem?
Please Help.

Make sure you explicitly specify the charset to use in each case. At the moment you are relying on the default, which may vary between platforms.
Try the alternative InputStreamReader constructor instead:
new InputStreamReader(fis, "UTF-8")