覆盖 URLConnection 的 getInputStream 以通过自定义协议接收数据

Question

我正在使用 Java Web Start 来获取和启动应用程序，为此我必须通过所谓的 jnlp 协议下载数据。由于此协议默认情况下 Java 未知，因此我不得不编写自己的 URL 流处理程序。

我的问题是我不知道如何实现getInputStream方法，

// the custom URL stream handler
URL.setURLStreamHandlerFactory((String protocol)
    -> "jnlp".equals(protocol) ? new URLStreamHandler() {
    @Override
    protected URLConnection openConnection(URL url) throws IOException {
        return new URLConnection(url) {
            @Override
            public void connect() throws IOException {
                System.out.println("connected");
            }
            @Override
            public InputStream getInputStream() throws IOException {
                /* -------------------- */
                /* What to put in here? */
                /* -------------------- */
            }
        };
    }
} : null);

// Constructing the parametrized URL for Java Web Start...
URL url = new URL("jnlp", "localhost", 8080,
    "application-connector/app?"
    + params.entrySet().stream().map(Object::toString)
        .collect(joining("&")));

// Downloading and starting the application...
final File jnlp = File.createTempFile("temp", ".jnlp");
byte[] buffer = new byte[8192];
int len;
while ((len = url.openStream().read(buffer)) != -1) {
    new FileOutputStream(jnlp).write(buffer, 0, len);
}
Desktop.getDesktop().open(jnlp);

这是必要的，这样我就不会收到以下错误：

protocol doesn't support input

Answer 1

通常只能从 http://https: URL 下载 JNLP。例如。 :

    URL url = new URL(
            "https://docs.oracle.com/javase/tutorialJWS/samples/uiswing/WallpaperProject/Wallpaper.jnlp");

    // Downloading and starting the application...
    final File jnlp = File.createTempFile("temp", ".jnlp");

    try (InputStream is = url.openStream();
            FileOutputStream fos = new FileOutputStream(jnlp)) {
        byte[] buffer = new byte[8192];
        int len;
        while ((len = is.read(buffer)) != -1) {
            fos.write(buffer, 0, len);
        }
    }

    System.out.println("JNLP file written to " + jnlp.getAbsolutePath());

    //Desktop.getDesktop().open(jnlp);
    new ProcessBuilder("cmd", "/c", "javaws", jnlp.getAbsolutePath())
            .start();

不确定这适用于什么环境。在 Windows 下，我发现 Desktop.open() 没有启动，因此直接调用 javaws.

如果直接调用 javaws 是一种选择，那么还有一种更简单的方法，因为它可以直接从 URL:

启动 JNLP 文件

    new ProcessBuilder("cmd", "/c", "javaws",
            "https://docs.oracle.com/javase/tutorialJWS/samples/uiswing/WallpaperProject/Wallpaper.jnlp")
                    .start();

覆盖 URLConnection 的 getInputStream 以通过自定义协议接收数据

Overriding getInputStream of URLConnection to receive data through a custom protocol

java

inputstream

java-web-start

jnlp

urlconnection