Why would a java net ConnectException Connection timed out exception occur when URL is up

Question

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  lt init gt  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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

try to do the Telnet to see any firewall issue perform tracert traceroute to find number of hops

User · Answer

There is a possibility that your IP host are blocked by the remote host  especially if it thinks you are hitting it too hard

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

There is a possibility that your IP host are blocked by the remote host  especially if it thinks you are hitting it too hard

User · Answer

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    Hope this helps

User · Answer

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

User · Answer

I solved my problem with   System setProperty  https proxyHost    myProxy    System setProperty  https proxyPort    80      or http proxyHost

User · Answer

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

User · Answer

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    Hope this helps

User · Answer

There is a possibility that your IP host are blocked by the remote host  especially if it thinks you are hitting it too hard

User · Answer

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    Hope this helps

User · Answer

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

User · Answer

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

User · Answer

There is a possibility that your IP host are blocked by the remote host  especially if it thinks you are hitting it too hard

User · Answer

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

User · Answer

try to do the Telnet to see any firewall issue perform tracert traceroute to find number of hops

User · Answer

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    Hope this helps

User · Answer

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

User · Answer

try to do the Telnet to see any firewall issue perform tracert traceroute to find number of hops

User · Answer

I solved my problem with   System setProperty  https proxyHost    myProxy    System setProperty  https proxyPort    80      or http proxyHost

User · Answer

try to do the Telnet to see any firewall issue perform tracert traceroute to find number of hops

User · Answer

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

User · Answer

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

[java] Why would a "java.net.ConnectException: Connection timed out" exception occur when URL is up?

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