模拟post提交，保持session不变

public static String sendPost(String url, String param) {
PrintWriter out = null;
BufferedReader in = null;
String result = "";
try {
URL realUrl = new URL(url);
// 打开和URL之间的连接
URLConnection conn = realUrl.openConnection();

// 第二次发送post，设置cookie与第一次获取到的值相同
if (cookieStore != null) {
conn.setRequestProperty("Cookie", "JSESSIONID="
+ cookieStore.getCookies().get(0).getValue());
}

// 设置通用的请求属性
conn.setRequestProperty("accept", "*/*");
conn.setRequestProperty("connection", "Keep-Alive");
conn.setRequestProperty("user-agent",
"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");

// 发送POST请求必须设置如下两行

conn.setDoOutput(true);
conn.setDoInput(true);
// 获取URLConnection对象对应的输出流

out = new PrintWriter(conn.getOutputStream());
// 发送请求参数

out.print(param);
// flush输出流的缓冲

out.flush();
// 定义BufferedReader输入流来读取URL的响应

in = new BufferedReader(
new InputStreamReader(conn.getInputStream()));

// 第一次登陆，设置cookie
if (cookieStore == null) {
String cookieValue = conn.getHeaderField("Set-Cookie");

String sessionId = cookieValue.substring(0,
cookieValue.indexOf(";"));
// System.out.println("cookie value:" + sessionId);

cookieStore = new BasicCookieStore();
BasicClientCookie cookie = new BasicClientCookie("JSESSIONID",
sessionId.split("=")[1]);
cookie.setVersion(0);
cookie.setDomain("domain");
cookie.setPath("/xxx");
cookieStore.addCookie(cookie);
}

String line;
while ((line = in.readLine()) != null) {
result += line;
}
} catch (Exception e) {
System.out.println("发送 POST 请求出现异常！" + e);
}
// 使用finally块来关闭输出流、输入流

finally {
try {
if (out != null) {
out.close();
}
if (in != null) {
in.close();
}
} catch (IOException ex) {
System.out.println("发送 POST 请求出现异常！" + ex);
}
}
return result;
}