HttpURLConnection getting locked

入职了一家做金融大数据的公司，终于走向Java开发者的正轨了~

最近遇到一个问题，服务器多线程程序在运行时，偶尔线程会发生死锁，进程在内存中不能释放，该程序会先删除数据库的表，执行完毕会新生成数据。这样就导致了数据库的表被清空，于是开始调查：

ps -aux|grep app
ps -eLf|grep app
jstack -l pid > pid.log

找到了问题所在，就是在 调用java 的HttpURLConnection 获取线上数据时，发生超时了：

at java.io.BufferedInputStream.read(BufferedInputStream.java:345)
- locked <0x0000000674b25db8> (a java.io.BufferedInputStream)
at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:704)
at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:647)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1535)
- locked <0x0000000674b1a7a0> (a sun.net.www.protocol.http.HttpURLConnection)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1440)
- locked <0x0000000674b1a7a0> (a sun.net.www.protocol.http.HttpURLConnection)
at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:480)

解决方案：

第一步追加 设置从主机读取的超时设置

URL url = new URL(urlStr);
HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
httpConn.setConnectTimeout(3000);
httpConn.setReadTimeout(3000);//add
httpConn.setDoInput(true);
httpConn.setRequestMethod("GET");
httpConn.connect();//add

第二步追加多次链接尝试：

json = getJsonContent(URL);
int i = 0;
while (StringUtils.isEmpty(json) && i < 3) {
json = getJsonContent(URL);
i++;
}