注册并使用自定义java.net.URL协议 [英] Registering and using a custom java.net.URL protocol

问题描述

我试图从我的java程序中调用自定义URL ，因此我使用了这样的东西：

I was trying to invoke a custom url from my java program, hence I used something like this:

URL myURL;
try {
   myURL = new URL("CustomURI:");
   URLConnection myURLConnection = myURL.openConnection();
   myURLConnection.connect();
} catch (Exception e) {
   e.printStackTrace();
}

我得到以下例外：

java.net.MalformedURLException：未知协议：java.net.URL中的CustomURI
。（未知来源）java.net.URL上的
。（未知来源）
at java.net.URL。（未知来源）
at com.demo.TestDemo.main（TestDemo.java:14）

java.net.MalformedURLException: unknown protocol: CustomURI at java.net.URL.(Unknown Source) at java.net.URL.(Unknown Source) at java.net.URL.(Unknown Source) at com.demo.TestDemo.main(TestDemo.java:14)

如果我从浏览器触发 URI ，那么它会按预期工作但如果我尝试从调用它Java程序然后我得到上述异常。

If I trigger the URI from a browser then it works as expected but if I try to invoke it from the Java Program then I am getting the above exception.

编辑：

以下是我尝试的步骤（我遗漏了一些东西）当然，请告诉我）：

Below are the steps I tried (I am missing something for sure, please let me know on that):

步骤1：在中添加自定义URI> java.protocol.handler.pkgs

Step 1: Adding the Custom URI in java.protocol.handler.pkgs

第2步：从网址触发自定义URI

代码：

public class CustomURI {

public static void main(String[] args) {

    try {
        add("CustomURI:");
        URL uri = new URL("CustomURI:");
        URLConnection uc = uri.openConnection();            
        uc.connect();
    } catch (Exception e) {
        e.printStackTrace();
    }

}

public static void add( String handlerPackage ){

    final String key = "java.protocol.handler.pkgs";

    String newValue = handlerPackage;
    if ( System.getProperty( key ) != null )
    {
        final String previousValue = System.getProperty( key );
        newValue += "|" + previousValue;
    }
    System.setProperty( key, newValue );
    System.out.println(System.getProperty("java.protocol.handler.pkgs"));

}

}

当我跑步时这段代码，我在我的控制台中打印了 CustomURI：（来自add方法），但是当 URL 初始化为 CustomURI：作为构造函数：

When I run this code, I am getting the CustomURI: printed in my console (from the add method) but then I am getting this exception when the URL is initialized with CustomURI: as a constructor:

Exception in thread "main" java.lang.StackOverflowError
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at java.net.URL.getURLStreamHandler(Unknown Source)
at java.net.URL.<init>(Unknown Source)
at java.net.URL.<init>(Unknown Source)
at sun.misc.URLClassPath$FileLoader.getResource(Unknown Source)
at sun.misc.URLClassPath.getResource(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.net.URL.getURLStreamHandler(Unknown Source)
at java.net.URL.<init>(Unknown Source)
at java.net.URL.<init>(Unknown Source)

请建议如何使这项工作。

Please advice how to make this work.

推荐答案

1. 创建自定义 URLConnection 在 connect（）方法中执行作业的实现。

1. Create a custom URLConnection implementation which performs the job in connect() method.

public class CustomURLConnection extends URLConnection {

    protected CustomURLConnection(URL url) {
        super(url);
    }

    @Override
    public void connect() throws IOException {
        // Do your job here. As of now it merely prints "Connected!".
        System.out.println("Connected!");
    }

}

不要忘记覆盖和相应地实现其他方法，如 getInputStream（）。由于此信息在问题中缺失，因此无法提供更多详细信息。

Don't forget to override and implement other methods like getInputStream() accordingly. More detail on that cannot be given as this information is missing in the question.

创建自定义 URLStreamHandler 实施哪个在 openConnection（）中返回它。

Create a custom URLStreamHandler implementation which returns it in openConnection().

public class CustomURLStreamHandler extends URLStreamHandler {

    @Override
    protected URLConnection openConnection(URL url) throws IOException {
        return new CustomURLConnection(url);
    }

}

不要忘记覆盖和必要时实施其他方法。

Don't forget to override and implement other methods if necessary.

创建自定义 URLStreamHandlerFactory ，根据协议创建并返回它。

Create a custom URLStreamHandlerFactory which creates and returns it based on the protocol.

public class CustomURLStreamHandlerFactory implements URLStreamHandlerFactory {

    @Override
    public URLStreamHandler createURLStreamHandler(String protocol) {
        if ("customuri".equals(protocol)) {
            return new CustomURLStreamHandler();
        }

        return null;
    }

}

请注意协议总是小写。

最后通过 URL #setURLStreamHandlerFactory（）

URL.setURLStreamHandlerFactory(new CustomURLStreamHandlerFactory());

请注意Javadoc 明确表示您最多可以设置一次。因此，如果您打算在同一个应用程序中支持多个自定义协议，则需要生成自定义 URLStreamHandlerFactory 实现，以便在 createURLStreamHandler中覆盖它们。 （）方法。

Note that the Javadoc explicitly says that you can set it at most once. So if you intend to support multiple custom protocols in the same application, you'd need to generify the custom URLStreamHandlerFactory implementation to cover them all inside the createURLStreamHandler() method.

或者，如果您不喜欢得墨忒耳定律，请全部扔掉一起用于代码缩小的匿名类：

Alternatively, if you dislike the Law of Demeter, throw it all together in anonymous classes for code minification:

URL.setURLStreamHandlerFactory(new URLStreamHandlerFactory() {
    public URLStreamHandler createURLStreamHandler(String protocol) {
        return "customuri".equals(protocol) ? new URLStreamHandler() {
            protected URLConnection openConnection(URL url) throws IOException {
                return new URLConnection(url) {
                    public void connect() throws IOException {
                        System.out.println("Connected!");
                    }
                };
            }
        } : null;
    }
});

如果您已经使用Java 8，请替换 URLStreamHandlerFactory lambda的功能接口进一步缩小：

If you're on Java 8 already, replace the URLStreamHandlerFactory functional interface by a lambda for further minification:

URL.setURLStreamHandlerFactory(protocol -> "customuri".equals(protocol) ? new URLStreamHandler() {
    protected URLConnection openConnection(URL url) throws IOException {
        return new URLConnection(url) {
            public void connect() throws IOException {
                System.out.println("Connected!");
            }
        };
    }
} : null);

---

现在你可以按如下方式使用它：

---

Now you can use it as follows:

URLConnection connection = new URL("CustomURI:blabla").openConnection();
connection.connect();
// ...

或根据规范使用小写协议：

Or with lowercased protocol as per the spec:

URLConnection connection = new URL("customuri:blabla").openConnection();
connection.connect();
// ...

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