blocks|key|1565886|text|为什么不直接使用基于时间戳的东西呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1565887|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Why not just use something based on a timestamp..?

blocks|key|1565984|text|嗯，你可以使用3参数版本：File.createTempFile(String+prefix,+String+suffix,+File+directory)，它可以让你把它放在你想放的地方。除非您告诉它，否则Java不会将它与任何其他文件区别对待。唯一的缺点是保证文件名的长度至少为8个字符(最少3个字符作为前缀，加上由函数生成的5个或更多字符)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1565985|如果这对你来说太长了，我想你总是可以从文件名"a“开始，然后遍历"b"，"c"，等等，直到你找到一个不存在的文件名。|1565986|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/javase/6/docs/api/java/io/File.html#createTempFile(java.lang.String,%2520java.lang.String,%2520java.io.File)^0|D|1T|D|1T|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

Well, you could use the 3-argument version: <a href="http://java.sun.com/javase/6/docs/api/java/io/File.html#createTempFile(java.lang.String,%20java.lang.String,%20java.io.File)" rel="noreferrer"><code>File.createTempFile(String prefix, String suffix, File directory)</code></a> which will let you put it where you'd like. Unless you tell it to, Java won't treat it differently than any other file. The only drawback is that the filename is guaranteed to be at least 8 characters long (minimum of 3 characters for the prefix, plus 5 or more characters generated by the function).

If that's too long for you, I suppose you could always just start with the filename "a", and loop through "b", "c", etc until you find one that doesn't already exist.

blocks|key|1566053|text|看看File+javadoc，createNewFile方法将仅在文件不存在时创建该文件，并将返回一个布尔值来说明该文件是否已创建。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1566054|您还可以使用exists()方法：|1566055|int+i+=+0;
String+filename+=+Integer.toString(i);
File+f+=+new+File(filename);
while+(f.exists())+{
++++i%2B%2B;
++++filename+=+Integer.toString(i);
++++f+=+new+File(filename);
}
f.createNewFile();
System.out.println("File+in+use:+"+%2B+f);|code-block|syntax|javascript|1566056|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/javase/6/docs/api/java/io/File.html^0|2|C|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|C|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

Look at the <a href="http://java.sun.com/javase/6/docs/api/java/io/File.html" rel="nofollow noreferrer">File javadoc</a>, the method createNewFile will create the file only if it doesn't exist, and will return a boolean to say if the file was created.

You may also use the exists() method:

<pre><code>int i = 0;
String filename = Integer.toString(i);
File f = new File(filename);
while (f.exists()) {
 i++;
 filename = Integer.toString(i);
 f = new File(filename);
}
f.createNewFile();
System.out.println("File in use: " + f);
</code></pre>

blocks|key|1350706|text|如何生成基于时间戳四舍五入到最接近的毫秒，或任何你需要的精度…然后使用锁来同步对函数的访问。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1350707|如果存储最后生成的文件名，则可以根据需要向其追加连续的字母或进一步的数字，以使其具有唯一性。|1350708|或者，如果您不想使用锁，可以使用一个时间步加一个线程ID，并确保函数的执行时间超过一毫秒，或者等待，这样它就会执行。|1350709|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

How about generate based on time stamp rounded to the nearest millisecond, or whatever accuracy you need... then use a lock to synchronize access to the function.

If you store the last generated file name, you can append sequential letters or further digits to it as needed to make it unique. 

Or if you'd rather do it without locks, use a time step plus a thread ID, and make sure that the function takes longer than a millisecond, or waits so that it does.

blocks|key|1350736|text|组合其他答案，为什么不使用附加了随机值的ms时间戳；重复直到没有冲突，实际上几乎永远不会发生冲突。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1350737|例如:File-ccyymmdd-hhmmss-mmm-rrrrr.txt|1350738|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Combining other answers, why not use the ms timestamp with a random value appended; repeat until no conflict, which in practice will be almost never.

For example: File-ccyymmdd-hhmmss-mmm-rrrrrr.txt

blocks|key|1566236|text|如果您有权访问数据库，则可以在文件名中创建和使用序列。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1566237|select+mySequence.nextval+from+dual;|code-block|syntax|javascript|1566238|它将保证是唯一的，并且不会变得太大(除非你正在输出大量的文件)。|1566239|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If you have access to a database, you can create and use a sequence in the file name. 

<pre><code>select mySequence.nextval from dual;
</code></pre>

It will be guaranteed to be unique and shouldn't get too large (unless you are pumping out a ton of files).

blocks|key|1350877|text|看起来您已经有了一些创建唯一文件名的解决方案，所以我就不提了。我会这样测试文件名：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1350878|++++String+filePath;
++++boolean+fileNotFound+=+true;
++++while+(fileNotFound)+{
++++++++String+testPath+=+generateFilename();

++++++++try+{
++++++++++++RandomAccessFile+f+=+new+RandomAccessFile(
++++++++++++++++new+File(testPath),+"r");
++++++++}+catch+(Exception+e)+{
++++++++++++//+exception+thrown+by+RandomAccessFile+if+
++++++++++++//+testPath+doesn't+exist+(ie:+it+can't+be+read)

++++++++++++filePath+=+testPath;
++++++++++++fileNotFound+=+false;
++++++++}
++++}
++++//now+create+your+file+with+filePath|code-block|syntax|javascript|1350879|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

It looks like you've got a handful of solutions for creating a unique filename, so I'll leave that alone. I would test the filename this way:

<pre><code> String filePath;
 boolean fileNotFound = true;
 while (fileNotFound) {
 String testPath = generateFilename();

 try {
 RandomAccessFile f = new RandomAccessFile(
 new File(testPath), "r");
 } catch (Exception e) {
 // exception thrown by RandomAccessFile if 
 // testPath doesn't exist (ie: it can't be read)

 filePath = testPath;
 fileNotFound = false;
 }
 }
 //now create your file with filePath
</code></pre>

blocks|key|1566325|text|这对我来说很有效：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1566326|String+generateUniqueFileName()+{
++++String+filename+=+"";
++++long+millis+=+System.currentTimeMillis();
++++String+datetime+=+new+Date().toGMTString();
++++datetime+=+datetime.replace("+",+"");
++++datetime+=+datetime.replace(":",+"");
++++String+rndchars+=+RandomStringUtils.randomAlphanumeric(16);
++++filename+=+rndchars+%2B+"_"+%2B+datetime+%2B+"_"+%2B+millis;
++++return+filename;
}|code-block|syntax|javascript|1566327|//+USE:|offset|length|style|CODE|1566328|String+newFile;
do{
newFile=generateUniqueFileName()+%2B+"."+%2B+FileExt;
}
while(new+File(basePath%2BnewFile).exists());|1566329|输出文件名应如下所示：|1566330|2OoBwH8OwYGKW2QE_4Sep2013061732GMT_1378275452253.Ext|1566331|entityMap^0|0|0|0|7|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

This works for me:

<pre><code>String generateUniqueFileName() {
 String filename = "";
 long millis = System.currentTimeMillis();
 String datetime = new Date().toGMTString();
 datetime = datetime.replace(" ", "");
 datetime = datetime.replace(":", "");
 String rndchars = RandomStringUtils.randomAlphanumeric(16);
 filename = rndchars + "_" + datetime + "_" + millis;
 return filename;
}
</code></pre>

<code>// USE:</code>

<pre><code>String newFile;
do{
newFile=generateUniqueFileName() + "." + FileExt;
}
while(new File(basePath+newFile).exists());
</code></pre>

Output filenames should look like :

<pre><code>2OoBwH8OwYGKW2QE_4Sep2013061732GMT_1378275452253.Ext
</code></pre>

blocks|key|1566360|text|这也是可行的|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1566361|String+logFileName+=+new+SimpleDateFormat("yyyyMMddHHmm'.txt'").format(new+Date());

logFileName+=+"loggerFile_"+%2B+logFileName;|code-block|syntax|javascript|1566362|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This also works

<pre><code>String logFileName = new SimpleDateFormat("yyyyMMddHHmm'.txt'").format(new Date());

logFileName = "loggerFile_" + logFileName;
</code></pre>

blocks|key|1351006|text|我知道我回答这个问题已经太晚了。但我认为我应该把它放在这里，因为它看起来与其他解决方案不同。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1351007|我们可以将threadname和当前的timeStamp连接起来作为文件名。但是有一个问题，例如一些线程名称包含特殊字符，如"\“，这可能会在创建文件名时产生问题。因此我们可以从线程名中删除特殊字符，然后将线程名和时间戳连接起来|1351008|fileName+=+threadName(after+removing+special+charater)+%2B+currentTimeStamp|code-block|syntax|javascript|1351009|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I understand that I am too late to reply on this question. But I think I should put this as it seems something different from other solution.

We can concatenate threadname and current timeStamp as file name. But with this there is one issue like some thread name contains special character like "\" which can create problem in creating file name. So we can remove special charater from thread name and then concatenate thread name and time stamp

<pre><code>fileName = threadName(after removing special charater) + currentTimeStamp
</code></pre>

blocks|key|1566509|text|为什么不使用同步来处理多线程呢？这是我的解决方案，它可以生成一个简短的文件名，而且它是唯一的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1566510|private+static+synchronized+String+generateFileName(){
++++String+name+=+make(index);
++++index+%2B%2B;
++++return+name;
}
private+static+String+make(int+index)+{
++++if(index+==+0)+return+"";
++++return+String.valueOf(chars[index+%25+chars.length])+%2B+make(index+/+chars.length);
}
private+static+int+index+=+1;
private+static+char[]+chars+=+{'a','b','c','d','e','f','g',
++++++++'h','i','j','k','l','m','n',
++++++++'o','p','q','r','s','t',
++++++++'u','v','w','x','y','z'};|code-block|syntax|javascript|1566511|blew是测试的主要功能，它是工作。|1566512|public+static+void+main(String[]+args)+{
++++List<String>+names+=+new+ArrayList<>();
++++List<Thread>+threads+=+new+ArrayList<>();
++++for+(int+i+=+0;+i+<+100;+i%2B%2B)+{
++++++++Thread+thread+=+new+Thread(new+Runnable()+{
++++++++++++@Override
++++++++++++public+void+run()+{
++++++++++++++++for+(int+i+=+0;+i+<+1000;+i%2B%2B)+{
++++++++++++++++++++String+name+=+generateFileName();
++++++++++++++++++++names.add(name);
++++++++++++++++}
++++++++++++}
++++++++});
++++++++thread.run();
++++++++threads.add(thread);
++++}

++++for+(int+i+=+0;+i+<+10;+i%2B%2B)+{
++++++++try+{
++++++++++++threads.get(i).join();
++++++++}+catch+(InterruptedException+e)+{
++++++++++++e.printStackTrace();
++++++++}
++++}

++++System.out.println(names);
++++System.out.println(names.size());

}|1566513|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Why not use synchronized to process multi thread.
here is my solution,It's can generate a short file name , and it's unique.

<pre><code>private static synchronized String generateFileName(){
 String name = make(index);
 index ++;
 return name;
}
private static String make(int index) {
 if(index == 0) return "";
 return String.valueOf(chars[index % chars.length]) + make(index / chars.length);
}
private static int index = 1;
private static char[] chars = {'a','b','c','d','e','f','g',
 'h','i','j','k','l','m','n',
 'o','p','q','r','s','t',
 'u','v','w','x','y','z'};
</code></pre>

blew is main function for test , It's work.

<pre><code>public static void main(String[] args) {
 List&lt;String&gt; names = new ArrayList&lt;&gt;();
 List&lt;Thread&gt; threads = new ArrayList&lt;&gt;();
 for (int i = 0; i &lt; 100; i++) {
 Thread thread = new Thread(new Runnable() {
 @Override
 public void run() {
 for (int i = 0; i &lt; 1000; i++) {
 String name = generateFileName();
 names.add(name);
 }
 }
 });
 thread.run();
 threads.add(thread);
 }

 for (int i = 0; i &lt; 10; i++) {
 try {
 threads.get(i).join();
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 }

 System.out.println(names);
 System.out.println(names.size());

}
</code></pre>

blocks|key|1566529|text|++++//Generating+Unique+File+Name
++++public+String+getFileName()+{
++++++++String+timeStamp+=+new+SimpleDateFormat("yyyy-MM-dd_HH:mm:ss").format(new+Date());
++++++++return+"PNG_"+%2B+timeStamp+%2B+"_.png";
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1566530|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code> //Generating Unique File Name
 public String getFileName() {
 String timeStamp = new SimpleDateFormat("yyyy-MM-dd_HH:mm:ss").format(new Date());
 return "PNG_" + timeStamp + "_.png";
 }
</code></pre>

blocks|key|1351161|text|问题是同步。隔离冲突区域。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1351162|将文件命名为：(server-name)_(thread/process-name)_(millisecond/timestamp).(extension)|offset|length|style|CODE|1351163|示例：aws1_t1_1447402821007.png|1351164|entityMap^0|0|7|1Z|0|3|P|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@$D|Q|E|R|F|G]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|K|$]]

Problem is synchronization. Separate out regions of conflict.

Name the file as : <code>(server-name)_(thread/process-name)_(millisecond/timestamp).(extension)</code>
 example : <code>aws1_t1_1447402821007.png</code>

blocks|key|1351207|text|我将当前毫秒与随机数一起使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1351208|i.e|1351209|Random+random=new+Random();
String+ext+=+".jpeg";
File+dir+=+new+File("/home/pregzt");
String+name+=+String.format("%25s%25s",System.currentTimeMillis(),random.nextInt(100000)%2Bext);
File+file+=+new+File(dir,+name);|code-block|syntax|javascript|1351210|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I use current milliseconds with random numbers 

i.e

<pre><code>Random random=new Random();
String ext = ".jpeg";
File dir = new File("/home/pregzt");
String name = String.format("%s%s",System.currentTimeMillis(),random.nextInt(100000)+ext);
File file = new File(dir, name);
</code></pre>

I don't necessarily want to use UUIDs since they are fairly long.

The file just needs to be unique within its directory.

One thought which comes to mind is to use <code>File.createTempFile(String prefix, String suffix)</code>, but that seems wrong because the file is not temporary.

The case of two files created in the same millisecond needs to be handled.

What is the best way to generate a unique and short file name in Java

数据库

Java

我不一定要使用UUID，因为它们相当长。该文件只需要在其目录中是唯一的。脑海中浮现的一个想法是使用File.createTempFile(String prefix, String suffix)，但这似乎是错误的，因为文件不是临时的。需要处理在同一毫秒内创建两个文件的情况。

问在Java中生成唯一且简短的文件名的最佳方法是什么
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