Java，"URI不能为空"简单HTTP客户端上的错误 [英] Java, "URI can't be null" error on simple HTTP client

问题描述

我正在尝试编写一个简单的HTTP客户端，该客户端具有给定的绝对HTTP路径，可以执行一个简单的HTTP GET请求并将其内容打印到标准输出中.

I'm trying to write a simple HTTP client that, given an absolute HTTP path, performs a simple HTTP GET request and prints out the content to standard output.

但是，我尝试加载的任何页面上都出现以下错误:

However, I'm getting the following error on any page I try to load:

    java.lang.IllegalArgumentException: URI can't be null.
    at sun.net.spi.DefaultProxySelector.select(DefaultProxySelector.java:141)
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:926)
    at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:850)
    at HTTrack.main(HTTrack.java:68)

引发异常的代码是:

try
{
    System.out.println("We will attempt to read " + getfilepath(args[0]) + " from " + getbasesite(args[0]));
    URL serverConnect = new URL("http", getbasesite(args[0]), getfilepath(args[0]));
    con = (HttpURLConnection)serverConnect.openConnection();
    con.setRequestMethod("GET");    
    con.setDoOutput(true);
    con.setReadTimeout(10000);
    System.out.println("Attempting to connect to " + getbasesite(args[0]) + " on port 80...");
    System.out.println("URL = " + con.getURL());
    con.connect();
    //System.out.println("Connection succeeded! Attempting to read remote file " + getfilepath(args[0]));
    BufferedReader br = new BufferedReader(new InputStreamReader(con.getInputStream()));
    String line = "";
    while((line = br.readLine()) != null)
    {
        System.out.println(line);
    }

}

引发异常(HTTrack.java:68)的行是con.connect()行，而函数getbasesite和getfilepath分别返回URL的服务器主机名和远程文件路径.

The line that is raising the exception (HTTrack.java:68) is the con.connect() line, and the functions getbasesite and getfilepath return the server host name and remote file paths of a URL, respectively.

例如，如果传递字符串http://www.somesite.com/somepage.html，则getbasesite将返回"www.somesite.com"，而getfilepath将返回"/somepage.html".我知道HttpURLConnection正确传递了这些值，因为当我调用getURL时，它将返回我期望的值:http://www.somesite.com/somepage.html

For example if passed the string http://www.somesite.com/somepage.html, getbasesite will return "www.somesite.com" and getfilepath will return "/somepage.html". I know the HttpURLConnection is being passed these values correctly because when I call getURL it returns what I expect: http://www.somesite.com/somepage.html

我对可能导致此错误的原因有所了解-我测试了HttpURLConnection类的确从带有System.out.println("URL = " + con.getURL());行的构造函数参数中获取了正确的URL，所以我不确定为什么尝试连接失败，并显示"URI不能为空"的错误.

I'm stuck as to what might be causing this error - I've tested that the HttpURLConnection class indeed gets the correct URL out of the constructor arguments with the line System.out.println("URL = " + con.getURL());, so I'm not sure why it's failing the attempts to connect with the error that the "URI can't be null".

推荐答案

尝试删除您的con.setDoOutput(true);或将其设置为false.该行告诉您将使用连接来写输出，但是稍后您将通过调用con.getInputStream()从流中读取.

Try removing your con.setDoOutput(true); or setting it to false. That line is telling your connection that you are going to be using it to write output, but then later on you are reading from the stream by calling con.getInputStream().

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