How to gracefully handle a FileNotFoundexception in java

Question

I'm trying to write a function which returns a file input stream. It looks something like this:

public FileInputStream getFileInputStream() {
    File file;
    try {
        file = new File("somepath");
    } catch (Exception e) {
    }
    FileInputStream fInputStream = new FileInputStream(file);
    return fInputStream;
}

So here is my problem - obviously a file isn't created in the case of an exception. But I NEED a file object to instantiate the FileInputStream. I'm kind of lost here, how can I handle the exception while still returning a valid FileInputStream object?

Everything that is subject to exceptional behavior should be wrapped in a `try...catch` block. That would mitigate your issue. — Makoto, Mar 09 '13 at 21:17
`new File("somepath")` will never throw an exception (though it may throw an error, theoretically). Why are you `try`ing it? — cheeken, Mar 09 '13 at 21:17
@cheeken is right - the only exception that could come from creating the file would be a NullPointerException, and that's mitigated by having a static string as the constructor. — Makoto, Mar 09 '13 at 21:18

Martijn Courteaux · Accepted Answer · 2013-03-09T21:29:47.683

12

That is the idea of throwing an exception further. Just throw the exception to the caller.

public FileInputStream getFileInputStream() throws FileNotFoundException
{
    File file = new File("somepath");
    FileInputStream fInputStream = new FileInputStream(file);
    return fInputStream;
}

This way, the caller has to handle it. This is the cleanest way of working with it.

Remark: You should know that instantiating a File object will never throw an Exception. It is the instantiation of the FileInputStream that might throw an Exception.

edited Mar 09 '13 at 21:29

answered Mar 09 '13 at 21:15

Martijn Courteaux

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I would `throws FileNotFoundException` as there is no need to broaden the type. – Peter Lawrey Mar 09 '13 at 21:24
I just learnt something. Thank you so much! – Kai Mar 10 '13 at 00:17

score 3 · Answer 2 · edited May 23 '17 at 11:53

3

Use File.exists(), it check wheater you can do something with a file.

UPD(Java FileOutputStream Create File if not exists):

File yourFile = new File("score.txt");
if(!yourFile.exists()) {
    yourFile.createNewFile();
} 
FileOutputStream oFile = new FileOutputStream(yourFile, false);

edited May 23 '17 at 11:53

Community

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answered Mar 09 '13 at 21:16

Mikhail

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@Makoto No, that's wrong. – Duncan Jones Mar 09 '13 at 21:19
@Makoto: That is not true. The file is created when you open an outputstream to it *or* call `File.createNewFile()`. – Martijn Courteaux Mar 09 '13 at 21:19
http://stackoverflow.com/questions/9620683/java-fileoutputstream-create-file-if-not-exists – Mikhail Mar 09 '13 at 21:23

score 0 · Answer 3 · answered Mar 09 '13 at 21:50

Here is the code I use. You might find it interesting.

public static final Charset UTF_8 = Charset.forName("UTF-8");

/**
 * Provide a normalised path name which can contain SimpleDateFormat syntax.
 * <p/>
 * e.g.  'directory/'yyyyMMdd would produce something like "directory/20130225"
 *
 * @param pathName to use. If it starts or ends with a single quote ' treat as a date format and use the current time
 * @return returns the normalise path.
 */
public static String normalisePath(String pathName) {
    if (pathName.startsWith("'") || pathName.endsWith("'"))
        return new SimpleDateFormat(pathName).format(new Date());
    return pathName;
}

/**
 * Convert a path to a Stream. It looks first in local file system and then the class path.
 * This allows you to override local any file int he class path.
 * <p/>
 * If the name starts with an =, treat the string as the contents.  Useful for unit tests
 * <p/>
 * If the name ends with .gz, treat the stream as compressed.
 * <p/>
 * Formats the name with normalisePath(String).
 *
 * @param name of path
 * @return as an InputStream
 * @throws IOException If the file was not found, or the GZIP Stream was corrupt.
 */
public static InputStream asStream(String name) throws IOException {
    String name2 = normalisePath(name);
    // support in memory files for testing purposes
    if (name2.startsWith("="))
        return new ByteArrayInputStream(name2.getBytes(UTF_8));
    InputStream in;
    try {
        in = new FileInputStream(name2);
    } catch (FileNotFoundException e) {
        in = Reflection.getCallerClass(3).getClassLoader().getResourceAsStream(name2);
        if (in == null)
            throw e;
    }
    if (name2.endsWith(".gz") || name2.endsWith(".GZ"))
        in = new GZIPInputStream(in);
    in = new BufferedInputStream(in);
    return in;
}

How to gracefully handle a FileNotFoundexception in java

3 Answers3