blocks|key|1048737|text|唯一正确的方法是下载它:)。在一些服务器上，通常你可以通过发出一个HEAD请求实例get请求来获得相同的url。这将只返回资源元数据，而不返回实际的文件内容。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1048738|更新:有关如何做到这一点的实际技术细节，请查看org.lif.java的答案。|1048739|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|$]]

The only true way is to download it :). On some servers usually you can get away by issuing a HEAD request insted of a GET request for the same url. This will return you only the resource metadata and not the actual file content. 

Update: Check org.life.java's answer for the actual technical details on how to do this.

blocks|key|834037|text|假设文件是通过http提供的，您可以向URL发送HEAD请求，并检查返回的http响应码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|834038|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|$]]

Assuming the file is being served through http, you can send a HEAD request to the URL and check the http response code returned.

blocks|key|834107|text|为它创建一个URLConnection。如果你成功了，它就存在了。您可能需要打开它的输入流，但不必读取内容。您可以立即关闭流。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|834108|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|$]]

Make a URLConnection to it. If you succeed, it exists. You may have to go so far as opening an input stream to it, but you don't have to read the contents. You can immediately close the stream.

blocks|key|834119|text|public+static+boolean+exists(String+URLName){
++++try+{
++++++HttpURLConnection.setFollowRedirects(false);
++++++//+note+:+you+may+also+need
++++++//++++++++HttpURLConnection.setInstanceFollowRedirects(false)
++++++HttpURLConnection+con+=
+++++++++(HttpURLConnection)+new+URL(URLName).openConnection();
++++++con.setRequestMethod("HEAD");
++++++return+(con.getResponseCode()+==+HttpURLConnection.HTTP_OK);
++++}
++++catch+(Exception+e)+{
+++++++e.printStackTrace();
+++++++return+false;
++++}
++}++|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|834120|Checking+if+a+URL+exists+or+not|unstyled|offset|length|834121|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/4177864/checking-a-url-exist-or-not^0|0|0|V|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|R|8|@]|9|@$G|S|H|T|1|U]]|A|$]]|$1|I|3|-4|5|F|7|V|8|@]|9|@]|A|$]]]|J|$K|$5|L|M|N|A|$O|P]]]]

<pre><code>public static boolean exists(String URLName){
 try {
 HttpURLConnection.setFollowRedirects(false);
 // note : you may also need
 // HttpURLConnection.setInstanceFollowRedirects(false)
 HttpURLConnection con =
 (HttpURLConnection) new URL(URLName).openConnection();
 con.setRequestMethod("HEAD");
 return (con.getResponseCode() == HttpURLConnection.HTTP_OK);
 }
 catch (Exception e) {
 e.printStackTrace();
 return false;
 }
 } 
</code></pre>

<a href="https://stackoverflow.com/questions/4177864/checking-a-url-exist-or-not">Checking if a URL exists or not</a>

blocks|key|834165|text|看看这个，它对我很有效。来源网址：Check+if+URL+exists+or+not+on+Server|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|834166|public+class+MainActivity+extends+Activity+{

@Override
protected+void+onCreate(Bundle+savedInstanceState)+{
++++super.onCreate(savedInstanceState);
++++setContentView(R.layout.activity_main);+++++

++++String+customURL+=+"http://www.desicomments.com/dc3/08/273858/273858.jpg";

++++MyTask+task+=+new+MyTask();
++++task.execute(customURL);
}


private+class+MyTask+extends+AsyncTask<String,+Void,+Boolean>+{

++++@Override
++++protected+void+onPreExecute()+{

++++}

++++@Override
++++protected+Boolean+doInBackground(String...+params)+{

+++++++++try+{
++++++++++++++++HttpURLConnection.setFollowRedirects(false);
++++++++++++++++HttpURLConnection+con+=++(HttpURLConnection)+new+URL(params[0]).openConnection();
++++++++++++++++con.setRequestMethod("HEAD");
++++++++++++++++System.out.println(con.getResponseCode());+
++++++++++++++++return+(con.getResponseCode()+==+HttpURLConnection.HTTP_OK);
++++++++++++}
++++++++++++catch+(Exception+e)+{+++
++++++++++++++++e.printStackTrace();++++
++++++++++++++++return+false;
++++++++++++}
++++}

++++@Override
++++protected+void+onPostExecute(Boolean+result)+{
++++++++boolean+bResponse+=+result;
+++++++++if+(bResponse==true)
++++++++++++{
++++++++++++++++Toast.makeText(MainActivity.this,+"File+exists!",+Toast.LENGTH_SHORT).show();++++++
++++++++++++}
++++++++++++else
++++++++++++{+++++++++++
++++++++++++++++Toast.makeText(MainActivity.this,+"File+does+not+exist!",+Toast.LENGTH_SHORT).show();
++++++++++++}++++++++++++++++++
++++}+++++++++++
}
}|code-block|syntax|javascript|834167|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/26418486/check-if-url-exists-or-not-on-server^0|H|10|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Check this, it works for me. Source URL: <a href="https://stackoverflow.com/questions/26418486/check-if-url-exists-or-not-on-server">Check if URL exists or not on Server</a>

<pre><code>public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main); 

 String customURL = "http://www.desicomments.com/dc3/08/273858/273858.jpg";

 MyTask task = new MyTask();
 task.execute(customURL);
}


private class MyTask extends AsyncTask&lt;String, Void, Boolean&gt; {

 @Override
 protected void onPreExecute() {

 }

 @Override
 protected Boolean doInBackground(String... params) {

 try {
 HttpURLConnection.setFollowRedirects(false);
 HttpURLConnection con = (HttpURLConnection) new URL(params[0]).openConnection();
 con.setRequestMethod("HEAD");
 System.out.println(con.getResponseCode()); 
 return (con.getResponseCode() == HttpURLConnection.HTTP_OK);
 }
 catch (Exception e) { 
 e.printStackTrace(); 
 return false;
 }
 }

 @Override
 protected void onPostExecute(Boolean result) {
 boolean bResponse = result;
 if (bResponse==true)
 {
 Toast.makeText(MainActivity.this, "File exists!", Toast.LENGTH_SHORT).show(); 
 }
 else
 { 
 Toast.makeText(MainActivity.this, "File does not exist!", Toast.LENGTH_SHORT).show();
 } 
 } 
}
}
</code></pre>

How can I check in Java if a file exists on a remote server (served by HTTP), having its URL? I don't want to download the file, just check its existence.

Check if file exists on remote server using its URL

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Java

如果文件存在于具有URL的远程服务器(由HTTP提供)上，我如何检入Java？我不想下载这个文件，只想检查它是否存在。

问使用文件的URL检查远程服务器上是否存在该文件
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