java - HttpURLConnection getInputStream读取页面，然后发出POST请求

Question

我尝试获取页面(HTML)，从中读取特殊 token (每次都不同)，然后发送 POST 请求，但这给了我java.lang.IllegalStateException:连接正在进行中

    final URL url = new URL("<...>");
    String token = null;
    final HttpURLConnection con = (HttpURLConnection) url.openConnection();
    try (final InputStreamReader isr = new InputStreamReader(con.getInputStream())) {
        try (final BufferedReader in = new BufferedReader(isr)) {
            String str;
            while ((str = in.readLine()) != null) {
                if (str.contains("__token")) {
                    token = str.replace("<...>", "").replace("<...>", "");
                    System.out.println(token);
                    break;
                }
            }
            in.close();
        }
        isr.close();
    }
    con.setRequestMethod("POST");
    con.setRequestProperty("User-Agent", USER_AGENT);
    con.setDoOutput(true);
    try (final DataOutputStream wr = new DataOutputStream(con.getOutputStream())) {
        final String params = getParams("par1", "par2", token);
        wr.writeBytes(params);
        wr.flush(); wr.close();
        final int responseCode = con.getResponseCode();
        System.out.println("\nSending 'POST' request to URL : " + url);
        System.out.println("Post parameters : " + params);
        System.out.println("Response Code : " + responseCode);
        try (final BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()))) {
            String inputLine;
            final StringBuilder response = new StringBuilder();
            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();
            System.out.println(response.toString());
        }
    }

如果我尝试从 cookie 获取此 token ，情况也是如此:

final String token=con.getHeaderField("Set-Cookie").replace("__Token=", "").replace("; path=/; HttpOnly", "");

如何正确地做到这一点？

Answer 1

documentation of HttpURLConnection说:

Each HttpURLConnection instance is used to make a single request but the underlying network connection to the HTTP server may be transparently shared by other instances.

这意味着您无法在同一个 HttpURLConnection 对象上创建新的 (POST) 请求。事实上，您会从中得到一个 IllegalStateException。

因此，您应该从 con 的定义中删除 final 修饰符，然后在完成原始 (GET) 请求的输出处理后，创建另一个连接:

con = (HttpURLConnection) url.openConnection();

只有这样，您才能继续构建 POST 请求。

<小时/>

一点注意:您使用 try-with-resources，因此不需要显式关闭流。此外，您不需要两个 try block 。事实上，您不需要保留对 InputStreamReader 的引用，因为 BufferedReader.close() 还会关闭底层 Reader，这还关闭底层的InputStream。