使用HttpURLConnection时遇到的资源未释放的问题

http://blog.sina.com.cn/s/blog_56beadc60100j9zu.html

今天自己写了一个压力测试的小程序,同时启100个线程，每个线程都串行地访问应用服务器上的一个jsp页面200次。在程序运行了一会儿以后，问题来了：

java.net.SocketException: No buffer space available (maximum connections reached?): connect

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.<init>(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)

到网上查了查，应该是资源耗尽了，但是没有找到解决的方法。
程序片断代码如下：

for (int j = 0; j < 200; j++) {

long beginTime = System.currentTimeMillis();

URL url = new URL("...");

HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();

httpURLConnection.setDoOutput(true);

httpURLConnection.setRequestMethod("POST");

OutputStream os = httpURLConnection.getOutputStream();

keywordNum = random.nextInt(myKeywords.length);

os.write(("keyword=" + myKeywords[keywordNum]).getBytes("UTF8"));

os.flush();

os.close();

int i = 0;

int contentLength = 0;

contentLength = httpURLConnection.getContentLength();

long endTime = System.currentTimeMillis();

System.out.println("Thread '" + name + "' search keyword '" + myKeywords[keywordNum] + "' and get content in " + (endTime - beginTime) + " Millis, length=" + contentLength);

}

后来想了想，既然资源没释放，释放就可以了。查了一下HttpURLConnection有个disconnect方法，但是加上后也没有用。再找，jdk的docs里说，HttpURLConnection这个对象关掉相关的InputStream和OutputStream可以释放掉相关资源，于是试了下，在contentLength = httpURLConnection.getContentLength();这行后面又加了2行：

InputStream is = httpURLConnection.getInputStream();

is.close();

问题解决了。
原来只是知道如果不调用httpURLConnection的getContentLength或其它get方法，请求是不会提交的，一般如果不需要也不会去调getInputStream，没想到还有个释放资源的问题。

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简单的概括下释放httpUrlConnection的资源就是:

调用HttpURLConnection的disConnecn方法，还要关掉关联的inputStream和outputStream