What's the difference between “java.io.IOException: Connection timed out” and “SocketTimeoutException: Read timed out”

问题

If I set a socket SoTimeout, and read from it. when read time exceed the timeout limit, I'll get an "SocketTimeoutException: Read timed out". and here is the stack in my case:

java.net.SocketTimeoutException: Read timed out
    at java.net.SocketInputStream.socketRead0(Native Method)
    at java.net.SocketInputStream.read(SocketInputStream.java:150)
    at java.net.SocketInputStream.read(SocketInputStream.java:121)
    at java.io.FilterInputStream.read(FilterInputStream.java:133)
    at org.apache.hadoop.ipc.Client$Connection$PingInputStream.read(Client.java:277)
    at java.io.BufferedInputStream.fill(BufferedInputStream.java:235)
    at java.io.BufferedInputStream.read(BufferedInputStream.java:254)
    at java.io.DataInputStream.readInt(DataInputStream.java:387)
    at org.apache.hadoop.ipc.Client$Connection.receiveResponse(Client.java:527)
    at org.apache.hadoop.ipc.Client$Connection.run(Client.java:462)

---

but here I encountered "IOExcetion: Connection timed out", i don't know how it happened. Stacks:

java.io.IOException: Connection timed out
    at sun.nio.ch.FileDispatcher.read0(Native Method)
    at sun.nio.ch.SocketDispatcher.read(SocketDispatcher.java:21)
    at sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:198)
    at sun.nio.ch.IOUtil.read(IOUtil.java:171)
    at sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:245)
    at org.apache.hadoop.net.SocketInputStream$Reader.performIO(SocketInputStream.java:55)
    at org.apache.hadoop.net.SocketIOWithTimeout.doIO(SocketIOWithTimeout.java:142)
    at org.apache.hadoop.net.SocketInputStream.read(SocketInputStream.java:155)
    at org.apache.hadoop.net.SocketInputStream.read(SocketInputStream.java:128)
    at java.io.FilterInputStream.read(FilterInputStream.java:116)
    at org.apache.hadoop.ipc.Client$Connection$PingInputStream.read(Client.java:277)
    at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
    at java.io.BufferedInputStream.read(BufferedInputStream.java:237)
    at java.io.DataInputStream.readInt(DataInputStream.java:370)
    at org.apache.hadoop.ipc.Client$Connection.receiveResponse(Client.java:527)
    at org.apache.hadoop.ipc.Client$Connection.run(Client.java:462)

Can someone tell me what's the differences between the two exceptions, Thanks.

回答1:

A connection timeout means you attempted to connect to the remote IP/port pair and failed to do so: it did not answer at all. Another possible error at that stage would be connection refused, in which this pair is available but rejected your connection attempt. Both of these errors appear on the initial setup of a socket. Note that these errors only occur with TCP, since a TCP connection requires the establishment of a session.

When you have a socket read timeout, it means you are connected, but failed to read data in time. Timeouts on sockets are configurable. You may also get a connection reset error, which means you did connect successfully, but the other end decided that after all you're not worth it :p

回答2:

Simple answer:

In one case (Connection timed out) your application cannot connect to the server in a timely manner. In the other case (Read timed out) the connection can be established but during read the connection times out.

回答3:

'Connection timed out' after the connect phase means that something has gone seriously wrong with the connection and it must be closed. 'Read timeout' just means that no data arrived within the specified receive timeout period: it isn't fatal.

来源：https://stackoverflow.com/questions/17147780/whats-the-difference-between-java-io-ioexception-connection-timed-out-and-s