问题

jsoup（版本1.11.2）请求数据时，超时时间设置为1分钟，但是30秒就超时了，爆出SocketTimeoutException：Read timed out。

示例代码

Connection.Response res = Jsoup.connect(url).timeout(60000).ignoreContentType(true) 

异常栈

java.net.SocketTimeoutException: Read timed out 
 
	at java.net.SocketInputStream.socketRead0(Native Method) 
	at java.net.SocketInputStream.socketRead(SocketInputStream.java:116) 
	at java.net.SocketInputStream.read(SocketInputStream.java:171) 
	at java.net.SocketInputStream.read(SocketInputStream.java:141) 
	at java.io.BufferedInputStream.fill(BufferedInputStream.java:246) 
	at java.io.BufferedInputStream.read1(BufferedInputStream.java:286) 
	at java.io.BufferedInputStream.read(BufferedInputStream.java:345) 
	at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:735) 
	at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:678) 
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1587) 
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1492) 
	at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:480) 
	at org.jsoup.helper.HttpConnection$Response.execute(HttpConnection.java:734) 
	at org.jsoup.helper.HttpConnection$Response.execute(HttpConnection.java:706) 
	at org.jsoup.helper.HttpConnection.execute(HttpConnection.java:299) 

保险起见，用wireshark抓了包，client端（192.168.8.12）发起请求后（366号包），server端（172.19.80.110）立刻响应了（368号包，只ACK，未携带数据），但是过了30秒后仍然未传输数据，所以client端断开链接，发送FIN报文（369号包）。

解决

首先，想到看java doc

/**
* Set the total request timeout duration. If a timeout occurs, an [email protected] java.net.SocketTimeoutException} will be thrown.
*

The default timeout is 30 seconds (30,000 millis). A timeout of zero is treated as an infinite timeout.
*

Note that this timeout specifies the combined maximum duration of the connection time and the time to read
* the full response.
* @param millis number of milliseconds (thousandths of a second) before timing out connects or reads.
* @return this Connection, for chaining
* @see #maxBodySize(int)
*/
Connection timeout(int millis);

按照javadoc的意思是，超时时间是connect 时间+read时间的总和，默认是30秒，这明显与实际不符。
根据异常栈，找到源代码

 
org.jsoup.helper.HttpConnection 
 
private static HttpURLConnection createConnection(Connection.Request req) throws IOException { 
            final HttpURLConnection conn = (HttpURLConnection) ( 
                req.proxy() == null ? 
                req.url().openConnection() : 
                req.url().openConnection(req.proxy()) 
            ); 
 
            conn.setRequestMethod(req.method().name()); 
            conn.setInstanceFollowRedirects(false); // don't rely on native redirection support 
            conn.setConnectTimeout(req.timeout()); 
            conn.setReadTimeout(req.timeout() / 2); // gets reduced after connection is made and status is read 
 
           //省略不相关代码 
 

注意，conn.setConnectTimeout(req.timeout()); connect timeout设置成了60s，但conn.setReadTimeout(req.timeout() / 2) 是30s（60/2）,正好印证了368号包与369号包相隔30秒。至此真想打包，jsoup的timeout并不完全如javadoc所说，正确的说法应该是，connect timeout是传入的timeout，read timeout是传入timeout的一半。

总结

其实这个问题，最终还是回到了基础知识：tcp的两个超时时间（IT虾米网），一个connect timeout，一个read timeout，分别对应java api中

java.net.Socket
connect timeout

connect(SocketAddress endpoint, int timeout)  
          将此套接字连接到服务器，并指定一个超时值。 

连接超时，是三次握手的时间。

read timeout

setSoTimeout(int timeout)  
          启用/禁用带有指定超时值的 SO_TIMEOUT，以毫秒为单位。 

read timeout是数据报文与数据报文之间的间隔时间，并不是读取全部内容的时间。

正确理解以上两个概念，有助于解决问题。