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Java建立长链接的方式_java http长链接(keep-alive)导致的问题

發布時間：2023/12/20 java 32 豆豆

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兩種由http長鏈接(keep-alive)導致的問題，當然這兩種問題都有多種原因導致，這里只分析針對keep-alive相關而產生的異常。

1 SocketException: Connection reset

報錯堆棧日志：

Caused by: java.net.SocketException: Connection reset

at java.net.SocketInputStream.read(SocketInputStream.java:209)

at java.net.SocketInputStream.read(SocketInputStream.java:141)

at org.apache.http.impl.io.SessionInputBufferImpl.streamRead(SessionInputBufferImpl.java:137)

at org.apache.http.impl.io.SessionInputBufferImpl.fillBuffer(SessionInputBufferImpl.java:153)

at org.apache.http.impl.io.SessionInputBufferImpl.readLine(SessionInputBufferImpl.java:282)

at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:138)

at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:56)

at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:259)

at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:163)

at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:165)

at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:273)

at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)

at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:272)

at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)

at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)

at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:111)

at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)

at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:72)

at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:221)

at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:165)

at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:140)

復制代碼

本質原因是服務器通過TCP協議給客戶端返回了RST消息，表示已經完成了發送和接收，如果客戶端此時從流中讀取數據時會發生Connection reset，往流中寫數據時就會發生Connection reset Connection reset by peer。注意Socket.close()語義和TCP FIN消息之間略有不匹配。

而至于為什么服務端會返回RST消息，那就是http keep-alive 導致的問題了。

如果是springboot的服務器，那么默認的keep-alive timeout是60s，如果客戶端使用的是apache httpclient，默認的keep-alive是在

org.apache.http.impl.client.DefaultConnectionKeepAliveStrategy類設置的，代碼如下：

public long getKeepAliveDuration(final HttpResponse response, final HttpContext context) {

Args.notNull(response, "HTTP response");

final HeaderElementIterator it = new BasicHeaderElementIterator(

response.headerIterator(HTTP.CONN_KEEP_ALIVE));

while (it.hasNext()) {

final HeaderElement he = it.nextElement();

final String param = he.getName();

final String value = he.getValue();

if (value != null && param.equalsIgnoreCase("timeout")) {

try {

return Long.parseLong(value) * 1000;

} catch(final NumberFormatException ignore) {

}

return -1;

}

復制代碼

可見，如果response header如果沒有返回Keep-Alive,那么就會是-1，也就是無限的，hc.apache.org/httpcompone… "If the Keep-Alive header is not present in the response, HttpClient assumes the connection can be kept alive indefinitely"

所以問題就比較明白了，springboot服務端沒有返回Keep-Alive的header，客戶端如果使用了apache httpclient，且沒有設置Keep-Alive的話，就會導致服務端的超時是60s,客戶端就認為是無限的，在某些情況下，服務端關閉了鏈接，客戶端還會獲取這個連接，就會導致上面的問題。

既然找到原因了那么就需要解決，httpclient文檔中也給了說要設置默認的超時時間，即給一個自定義的實現。

2 NoHttpResponseException: xxx.xxx.xxx.xxx failed to respond

Caused by: org.apache.http.NoHttpResponseException: xxx.xxx.xxx.xxx failed to respond

at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:141)