如何优雅地处理 Java 中的 FileNotFoundException
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How to gracefully handle a FileNotFoundexception in java
提问by Kai
I'm trying to write a function which returns a file input stream. It looks something like this:
我正在尝试编写一个返回文件输入流的函数。它看起来像这样：
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?
所以这是我的问题 - 显然在出现异常的情况下不会创建文件。但是我需要一个文件对象来实例化 FileInputStream。我有点迷失在这里，如何在仍然返回有效的 FileInputStream 对象的同时处理异常？
回答by Martijn Courteaux
That is the idea of throwing an exception further. Just throw the exception to the caller.
这就是进一步抛出异常的想法。只需将异常抛出给调用者。
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.
这样，调用者必须处理它。这是使用它的最干净的方式。
Remark: You should know that instantiating a Fileobject will never throw an Exception. It is the instantiation of the FileInputStreamthat might throw an Exception.
备注：您应该知道实例化File对象永远不会抛出异常。FileInputStream可能抛出异常的是 的实例化。
回答by Mikhail
Use File.exists(), it check wheater you can do something with a file.
使用File.exists()，它会检查您是否可以对文件执行某些操作。
UPD(Java FileOutputStream Create File if not exists):
UPD（Java FileOutputStream 创建文件，如果不存在）：
File yourFile = new File("score.txt");
if(!yourFile.exists()) {
yourFile.createNewFile();
}
FileOutputStream oFile = new FileOutputStream(yourFile, false);
回答by Peter Lawrey
Here is the code I use. You might find it interesting.
这是我使用的代码。你可能会觉得很有趣。
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;
}
