I'm in the process of writing two Junit testcases for testing the timemouts
#Test
public void connectionTimeoutTest()
{
String myurl = "http://serverip:serverport/context";
URL url = new URL(myurl);
URLConnection con = url.openConnection();
//how to check connectionTimeout but not socket time out
//what I think
//is it good enough to check with a server ip that does not exist ?
}
#Test
public void socketTimeoutTest()
{
String myurl = "http://localhost:serverport/context";
URL url = new URL(myurl);
URLConnection con = url.openConnection();
//how to check successful connection and timesout at socket (or port)
//what I think
//IP should exist (so it is localhost) but should not be listening on the port
}
I'm confused here because I'm not sure if my approach is right. What are the exceptions in each case ? Also, is it possible to differentiate based on Exceptions ?
Are there any other time outs that I have missed ?
Thanks in advance
You need to call URLConnection.setConnectTimeout() before opening any streams or getting the response code. It will throw a ConnectException with the text 'connection timed out' if a connect timeout happens.
Note that, contrary to the Javadoc, the default connect timeout is about a minute (platform-dependent), not infinity, and that you can decrease the default connection timeout this way, but not increase it.
For a read timeout, which I assume is what you mean by 'socket timeout', you have to call URLConnection.setReadTimeout(). If it fires, you will get a SocketTimeoutException. In this case zero does mean infinity as per the Javadoc.
I am not too clear on your unit test requirements. If you are to test the connection (and socket read) timeout values of the server, the approach mentioned above will only allow you to validate a certain "maximum" threshold value. But you still won't be able to confirm TCP server side timeout settings. The TCP server's connection (and read) timeouts depend upon factors such as platform (OS) and TCP stack implementation.
Again, the timeout setting via setConnectTimeout or setReadTimeout() are only on the client socket, when communicating with the resource referenced by this URLConnection.
In the first test case, I think it will get java.net.UnknownHostException, because of non-exist ip address.
If you wanna cause a socket connect timeout exception (exactly get messages like "java.net.SocketTimeoutException: connect timed out") , just use URLConnection.setConnectTimeout(10), set the parameter as smaller as possible ,but positive;
The same in the second test case, you can use URLConnection.setReadTimeout(10) to cause a read timeout exception ("java.net.SocketTimeoutException: Read timed out").
Related
So I have a problem with a Java program I have. The program's basic functionality includes basically connecting to a web API for data. The function that does that is something like this:
public static Object getData(String sURL) throws IOException {
URL url = new URL(sURL);
URLConnection request = url.openConnection();
request.connect();
return request.getContent();
}
The code works fine as it is, but recently, after my house changed ISPs, I have found that sometimes the connections take an unreasonably long amount of time, something like 10 seconds or more in about 10% of attempts, while the other 90% takes only around 200ms. I have found it to be faster to ask my program to call the function again in a different thread than to wait for some of these connections to finally connect.
Therefore, I want to change the function so that if after 500ms, the connection did not establish, it would disconnect and a new connection would be attempted. How could I do this?
Somewhere online I read that HttpURLConnection might help, but I am not sure how.
URLConnection allows you to specify the connect and read timeout prior to calling connect():
https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/URLConnection.html#setConnectTimeout(int)
Sets a specified timeout value, in milliseconds, to be used when
opening a communications link to the resource referenced by this
URLConnection. If the timeout expires before the connection can be
established, a java.net.SocketTimeoutException is raised. A timeout of
zero is interpreted as an infinite timeout.
With 500ms timeout:
try {
URLConnection request = url.openConnection();
request.setConnectTimeout(500); // 500 ms
request.connect();
// on successful connection
} catch (SocketTimeoutException ex) {
// on request timeout
}
This you can pack into a loop, but I recommend limiting the number of attempts made.
Java's URLConnection doesn't have retry capabilities in Java 8 therefore the best way here to achieve this - use an appropriate standalone 3-party library such as Apache HttpClient.
This is by far the best standalone 3-party HTTP client with advanced capabilities as of 2020 and it's still maintained.
By default as of version 5.2.x Apache Http Client, Apache Http Client uses the default implementation of org.apache.http.client.HttpRequestRetryHandler, which retries 3 times, but you can use a custom implementation instead.
The configuration might look like this(full imports are for example's sake):
org.apache.http.client.HttpClient httpClient = org.apache.http.impl.client.HttpClients.custom()
.setRetryHandler(YourCustomImplOfTheRetryHandlerClass)
//other config
.build();
There is no way I can reproduce that problem using my ISP.
I suggest you dig deeper into the problem and find a better solution. Sending another request just doesn't seem good enough to me. Maybe try a different way to get the data and see if that works for you. Can't say for sure as I can't reproduce the problem.
Given the code:
HttpURLConnection huc = (HttpURLConnection) new URL( url ).openConnection();
huc.setConnectTimeout( 10000 );
huc.connect();
how exactly the connection timeout is processed? Some HTTP header gets set or what? Or the connection status is being checked in a loop for connectionTimeout time?
I tried to find it in the source code, but there is only the long connectionTimout field...
Think of it as:
Inside connect first a parallel timer is run for the the connection timeout.
If the timer ends before the actual connection is established (response received), then fail.
In reality on most platforms the operating system can be parametrised with a timeout and will handle it oneself - in the same manner.
Not having seen the java native code, but there are POSIX methods like setsocketopt with which to set timeouts. POSIX connect will give a timeout.
In java the timeout was a later much desired addition to utilize these available timeouts.
This question already has answers here:
Java socket API: How to tell if a connection has been closed?
(9 answers)
Closed 5 years ago.
When I'm using e.g. PuTTY and my connection gets lost (or when I do a manual ipconfig /release on Windows), it responds directly and notifies my connection was lost.
I want to create a Java program which monitors my Internet connection (to some reliable server), to log the date/times when my internet fails.
I tried use the Socket.isConnected() method but that will just forever return "true". How can I do this in Java?
Well, the best way to tell if your connection is interrupted is to try to read/write from the socket. If the operation fails, then you have lost your connection sometime.
So, all you need to do is to try reading at some interval, and if the read fails try reconnecting.
The important events for you will be when a read fails - you lost connection, and when a new socket is connected - you regained connection.
That way you can keep track of up time and down time.
Even though TCP/IP is "connection oriented" protocol, normally no data is sent over an idle connection. You can have a socket open for a year without a single bit sent over it by the IP stack. In order to notice that a connection is lost, you have to send some data on the application level.(*) You can try this out by unplugging the phone cable from your ADSL modem. All connections in your PC should stay up, unless the applications have some kind of application level keepalive mechanism.
So the only way to notice lost connection is to open TCP connection to some server and read some data from it. Maybe the most simple way could be to connect to some FTP server and fetch a small file - or directory listing - once in a while. I have never seen a generic server which was really meant to be used for this case, and owners of the FTP server may not like clients doing this.
(*) There is also a mechanism called TCP keepalive but in many OS's you have to activate it for all applications, and it is not really practical to use if you want to notice loss of connection quickly
If the client disconnects properly, a read() will return -1, readLine() returns null, readXXX() for any other X throws EOFException. The only reliable way to detect a lost TCP connection is to write to it. Eventually this will throw an IOException 'connection reset', but it takes at least two writes due to buffering.
Why not use the isReachable() method of the java.net.InetAddress class?
How this works is JVM implementation specific but:
A typical implementation will use ICMP ECHO REQUESTs if the privilege can be obtained, otherwise it will try to establish a TCP connection on port 7 (Echo) of the destination host.
If you want to keep a connection open continually so you can see when that fails you could connect to server running the ECHO protocol yourself rather than having isReachable() do it for you and read and write data and wait for it to fail.
You might want to try looking at the socket timeout interval. With a short timeout (I believe the default is 'infinite timeout') then you might be able to trap an exception or something when the host becomes unreachable.
Okay so I finally got it working with
try
{
Socket s = new Socket("stackoverflow.com",80);
DataOutputStream os = new DataOutputStream(s.getOutputStream());
DataInputStream is = new DataInputStream(s.getInputStream());
while (true)
{
os.writeBytes("GET /index.html HTTP/1.0\n\n");
is.available();
Thread.sleep(1000);
}
}
catch (IOException e)
{
System.out.println("connection probably lost");
e.printStackTrace();
}
Not as clean as I hoped but it's not working if I leave out the os.writeBytes().
You could ping a machine every number of seconds, and this would be pretty accurate. Be careful that you don't DOS it.
Another alternative would be run a small server on a remote machine and keep a connection to it.
Its probably simpler to connect to yahoo/google or somewhere like this.
URL yahoo = new URL("http://www.yahoo.com/");
URLConnection yc = yahoo.openConnection();
int dataLen = yc.getContentLength() ;
Neil
The isConnected()method inside Socket.java class is a little misleading. It does not tell you if the socket is currently connected to a remote host (like if it is unclosed). Instead, it tells you whether the socket has ever been connected to a remote host. If the socket was able to connect to the remote host at all, this method returns true, even after that socket has been closed. To tell if a socket is currently open, you need to check that isConnected() returns true and isClosed() returns false.
For example:
boolean connected = socket.isConnected() && !socket.isClosed();
This question already has answers here:
Java socket API: How to tell if a connection has been closed?
(9 answers)
Closed 5 years ago.
When I'm using e.g. PuTTY and my connection gets lost (or when I do a manual ipconfig /release on Windows), it responds directly and notifies my connection was lost.
I want to create a Java program which monitors my Internet connection (to some reliable server), to log the date/times when my internet fails.
I tried use the Socket.isConnected() method but that will just forever return "true". How can I do this in Java?
Well, the best way to tell if your connection is interrupted is to try to read/write from the socket. If the operation fails, then you have lost your connection sometime.
So, all you need to do is to try reading at some interval, and if the read fails try reconnecting.
The important events for you will be when a read fails - you lost connection, and when a new socket is connected - you regained connection.
That way you can keep track of up time and down time.
Even though TCP/IP is "connection oriented" protocol, normally no data is sent over an idle connection. You can have a socket open for a year without a single bit sent over it by the IP stack. In order to notice that a connection is lost, you have to send some data on the application level.(*) You can try this out by unplugging the phone cable from your ADSL modem. All connections in your PC should stay up, unless the applications have some kind of application level keepalive mechanism.
So the only way to notice lost connection is to open TCP connection to some server and read some data from it. Maybe the most simple way could be to connect to some FTP server and fetch a small file - or directory listing - once in a while. I have never seen a generic server which was really meant to be used for this case, and owners of the FTP server may not like clients doing this.
(*) There is also a mechanism called TCP keepalive but in many OS's you have to activate it for all applications, and it is not really practical to use if you want to notice loss of connection quickly
If the client disconnects properly, a read() will return -1, readLine() returns null, readXXX() for any other X throws EOFException. The only reliable way to detect a lost TCP connection is to write to it. Eventually this will throw an IOException 'connection reset', but it takes at least two writes due to buffering.
Why not use the isReachable() method of the java.net.InetAddress class?
How this works is JVM implementation specific but:
A typical implementation will use ICMP ECHO REQUESTs if the privilege can be obtained, otherwise it will try to establish a TCP connection on port 7 (Echo) of the destination host.
If you want to keep a connection open continually so you can see when that fails you could connect to server running the ECHO protocol yourself rather than having isReachable() do it for you and read and write data and wait for it to fail.
You might want to try looking at the socket timeout interval. With a short timeout (I believe the default is 'infinite timeout') then you might be able to trap an exception or something when the host becomes unreachable.
Okay so I finally got it working with
try
{
Socket s = new Socket("stackoverflow.com",80);
DataOutputStream os = new DataOutputStream(s.getOutputStream());
DataInputStream is = new DataInputStream(s.getInputStream());
while (true)
{
os.writeBytes("GET /index.html HTTP/1.0\n\n");
is.available();
Thread.sleep(1000);
}
}
catch (IOException e)
{
System.out.println("connection probably lost");
e.printStackTrace();
}
Not as clean as I hoped but it's not working if I leave out the os.writeBytes().
You could ping a machine every number of seconds, and this would be pretty accurate. Be careful that you don't DOS it.
Another alternative would be run a small server on a remote machine and keep a connection to it.
Its probably simpler to connect to yahoo/google or somewhere like this.
URL yahoo = new URL("http://www.yahoo.com/");
URLConnection yc = yahoo.openConnection();
int dataLen = yc.getContentLength() ;
Neil
The isConnected()method inside Socket.java class is a little misleading. It does not tell you if the socket is currently connected to a remote host (like if it is unclosed). Instead, it tells you whether the socket has ever been connected to a remote host. If the socket was able to connect to the remote host at all, this method returns true, even after that socket has been closed. To tell if a socket is currently open, you need to check that isConnected() returns true and isClosed() returns false.
For example:
boolean connected = socket.isConnected() && !socket.isClosed();
I'm getting a ConnectException: Connection timed out with some frequency from my code. The URL I am trying to hit is up. The same code works for some users, but not others. It seems like once one user starts to get this exception they continue to get the exception.
Here is the stack trace:
java.net.ConnectException: Connection timed out
Caused by: java.net.ConnectException: Connection timed out
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
at java.net.Socket.connect(Socket.java:516)
at java.net.Socket.connect(Socket.java:466)
at sun.net.NetworkClient.doConnect(NetworkClient.java:157)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:365)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:477)
at sun.net.www.http.HttpClient.<init>(HttpClient.java:214)
at sun.net.www.http.HttpClient.New(HttpClient.java:287)
at sun.net.www.http.HttpClient.New(HttpClient.java:299)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:796)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:748)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:673)
at sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:840)
Here is a snippet from my code:
URLConnection urlConnection = null;
OutputStream outputStream = null;
OutputStreamWriter outputStreamWriter = null;
InputStream inputStream = null;
try {
URL url = new URL(urlBase);
urlConnection = url.openConnection();
urlConnection.setDoOutput(true);
outputStream = urlConnection.getOutputStream(); // exception occurs on this line
outputStreamWriter = new OutputStreamWriter(outputStream);
outputStreamWriter.write(urlString);
outputStreamWriter.flush();
inputStream = urlConnection.getInputStream();
String response = IOUtils.toString(inputStream);
return processResponse(urlString, urlBase, response);
} catch (IOException e) {
throw new Exception("Error querying url: " + urlString, e);
} finally {
IoUtil.close(inputStream);
IoUtil.close(outputStreamWriter);
IoUtil.close(outputStream);
}
Connection timeouts (assuming a local network and several client machines) typically result from
a) some kind of firewall on the way that simply eats the packets without telling the sender things like "No Route to host"
b) packet loss due to wrong network configuration or line overload
c) too many requests overloading the server
d) a small number of simultaneously available threads/processes on the server which leads to all of them being taken. This happens especially with requests that take a long time to run and may combine with c).
If the URL works fine in the web browser on the same machine, it might be that the Java code isn't using the HTTP proxy the browser is using for connecting to the URL.
The error message says it all: your connection timed out. This means your request did not get a response within some (default) timeframe. The reasons that no response was received is likely to be one of:
a) The IP/domain or port is incorrect
b) The IP/domain or port (i.e service) is down
c) The IP/domain is taking longer than your default timeout to respond
d) You have a firewall that is blocking requests or responses on whatever port you are using
e) You have a firewall that is blocking requests to that particular host
f) Your internet access is down
g) Your live-server is down i.e in case of "rest-API call".
Note that firewalls and port or IP blocking may be in place by your ISP
I'd recommend raising the connection timeout time before getting the output stream, like so:
urlConnection.setConnectTimeout(1000);
Where 1000 is in milliseconds (1000 milliseconds = 1 second).
try to do the Telnet to see any firewall issue
perform tracert/traceroute to find number of hops
I solved my problem with:
System.setProperty("https.proxyHost", "myProxy");
System.setProperty("https.proxyPort", "80");
or http.proxyHost...
Why would a “java.net.ConnectException: Connection timed out”
exception occur when URL is up?
Because the URLConnection (HttpURLConnection/HttpsURLConnection) is erratic. You can read about this here and here.
Our solution were two things:
a) set the ContentLength via setFixedLengthStreamingMode
b) catch any TimeoutException and retry if it failed.
This can be a IPv6 problem (the host publishes an IPv6 AAAA-Address and the users host thinks it is configured for IPv6 but it is actually not correctly connected). This can also be a network MTU problem, a firewall block, or the target host might publish different IP addresses (randomly or based on originators country) which are not all reachable. Or similliar network problems.
You cant do much besides setting a timeout and adding good error messages (especially printing out the hosts' resolved address). If you want to make it more robust add retry, parallel trying of all addresses and also look into name resolution caching (positive and negative) on the Java platform.
There is a possibility that your IP/host are blocked by the remote host, especially if it thinks you are hitting it too hard.
The reason why this happened to me was that a remote server was allowing only certain IP addressed but not its own, and I was trying to render the images from the server's URLs... so everything would simply halt, displaying the timeout error that you had...
Make sure that either the server is allowing its own IP, or that you are rendering things from some remote URL that actually exists.