blocks|key|819456|text|尝试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|819457|final+InputStream+is+=+new+URL("http://wwww.somewebsite.com/a.txt").openStream();|code-block|syntax|javascript|819458|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try:

<pre><code>final InputStream is = new URL("http://wwww.somewebsite.com/a.txt").openStream();
</code></pre>

blocks|key|604380|text|您的原始代码使用FileInputStream，它用于访问文件系统托管的文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|604381|您使用的构造函数将尝试在当前工作目录(系统属性user.dir的值)的www.somewebsite.com子文件夹中定位一个名为a.txt的文件。您提供的名称将使用file类解析为文件。|604382|URL对象是解决此问题的通用方法。您可以使用URL访问本地文件，也可以访问网络托管的资源。除了http://或https://之外，URL类还支持file://协议，所以您可以放心了。|604383|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Your original code uses FileInputStream, which is for accessing file system hosted files.

The constructor you used will attempt to locate a file named a.txt in the www.somewebsite.com subfolder of the current working directory (the value of system property user.dir). The name you provide is resolved to a file using the File class.

URL objects are the generic way to solve this. You can use URLs to access local files but also network hosted resources. The URL class supports the file:// protocol besides http:// or https:// so you're good to go.

blocks|key|604434|text|下面是一个完整的示例，它读取给定网页的内容。该网页是从HTML表单读取的。我们使用标准的InputStream类，但使用JSoup库可以更容易地完成这项工作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|604435|<dependency>
++++<groupId>javax.servlet</groupId>
++++<artifactId>javax.servlet-api</artifactId>
++++<version>3.1.0</version>
++++<scope>provided</scope>

</dependency>

<dependency>
++++<groupId>commons-validator</groupId>
++++<artifactId>commons-validator</artifactId>
++++<version>1.6</version>
</dependency>++|code-block|syntax|javascript|604436|这些是Maven依赖项。我们使用Apache+Commons库来验证URL字符串。|604437|package+com.zetcode.web;

import+com.zetcode.service.WebPageReader;
import+java.io.IOException;
import+java.nio.charset.StandardCharsets;
import+javax.servlet.ServletException;
import+javax.servlet.ServletOutputStream;
import+javax.servlet.annotation.WebServlet;
import+javax.servlet.http.HttpServlet;
import+javax.servlet.http.HttpServletRequest;
import+javax.servlet.http.HttpServletResponse;

@WebServlet(name+=+"ReadWebPage",+urlPatterns+=+{"/ReadWebPage"})
public+class+ReadWebpage+extends+HttpServlet+{

++++@Override
++++protected+void+doGet(HttpServletRequest+request,+HttpServletResponse+response)
++++++++++++throws+ServletException,+IOException+{

++++++++response.setContentType("text/plain;charset=UTF-8");

++++++++String+page+=+request.getParameter("webpage");

++++++++String+content+=+new+WebPageReader().setWebPageName(page).getWebPageContent();

++++++++ServletOutputStream+os+=+response.getOutputStream();
++++++++os.write(content.getBytes(StandardCharsets.UTF_8));
++++}
}|604438|ReadWebPage+servlet读取给定网页的内容，并以纯文本格式将其发送回客户机。读取页面的任务被委派给WebPageReader。|604439|package+com.zetcode.service;

import+java.io.BufferedReader;
import+java.io.IOException;
import+java.io.InputStream;
import+java.io.InputStreamReader;
import+java.net.URL;
import+java.nio.charset.StandardCharsets;
import+java.util.logging.Level;
import+java.util.logging.Logger;
import+java.util.stream.Collectors;
import+org.apache.commons.validator.routines.UrlValidator;

public+class+WebPageReader+{

++++private+String+webpage;
++++private+String+content;

++++public+WebPageReader+setWebPageName(String+name)+{

++++++++webpage+=+name;
++++++++return+this;
++++}

++++public+String+getWebPageContent()+{

++++++++try+{

++++++++++++boolean+valid+=+validateUrl(webpage);

++++++++++++if+(!valid)+{

++++++++++++++++content+=+"Invalid+URL;+use+http(s)://www.example.com+format";
++++++++++++++++return+content;
++++++++++++}

++++++++++++URL+url+=+new+URL(webpage);

++++++++++++try+(InputStream+is+=+url.openStream();
++++++++++++++++++++BufferedReader+br+=+new+BufferedReader(
++++++++++++++++++++++++++++new+InputStreamReader(is,+StandardCharsets.UTF_8)))+{

++++++++++++++++content+=+br.lines().collect(
++++++++++++++++++++++Collectors.joining(System.lineSeparator()));
++++++++++++}

++++++++}+catch+(IOException+ex)+{

++++++++++++content+=+String.format("Cannot+read+webpage+%25s",+ex);
++++++++++++Logger.getLogger(WebPageReader.class.getName()).log(Level.SEVERE,+null,+ex);
++++++++}

++++++++return+content;
++++}

++++private+boolean+validateUrl(String+webpage)+{

++++++++UrlValidator+urlValidator+=+new+UrlValidator();

++++++++return+urlValidator.isValid(webpage);
++++}
}|604440|WebPageReader验证该URL并读取网页内容。它返回一个包含页面HTML代码的字符串。|604441|<!DOCTYPE+html>
<html>
++++<head>
++++++++<title>Home+page</title>
++++++++<meta+charset="UTF-8">
++++</head>
++++<body>
++++++++<form+action="ReadWebPage">

++++++++++++<label+for="page">Enter+a+web+page+name:</label>
++++++++++++<input++type="text"+id="page"+name="webpage">

++++++++++++<button+type="submit">Submit</button>

++++++++</form>
++++</body>
</html>|604442|最后，这是包含HTML表单的主页。这篇文章摘自我关于这个话题的tutorial。|604443|entityMap|0|LINK|mutability|MUTABLE|url|http://zetcode.com/articles/javaservletreadwebpage/^0|18|B|0|0|0|0|0|B|1K|D|0|0|0|D|0|0|V|8|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1A|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1H|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|1I|8|@$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|U|3|V|5|H|7|1L|8|@]|D|@]|E|$I|J]]|$1|W|3|X|5|6|7|1M|8|@]|D|@$9|1N|A|1O|1|1P]]|E|$]]|$1|Y|3|-4|5|6|7|1Q|8|@]|D|@]|E|$]]]|Z|$10|$5|11|12|13|E|$14|15]]]]

Here is a full example which reads the contents of the given web page.
The web page is read from an HTML form. We use standard <code>InputStream</code> classes, but it could be done more easily with JSoup library.

<pre><code>&lt;dependency&gt;
 &lt;groupId&gt;javax.servlet&lt;/groupId&gt;
 &lt;artifactId&gt;javax.servlet-api&lt;/artifactId&gt;
 &lt;version&gt;3.1.0&lt;/version&gt;
 &lt;scope&gt;provided&lt;/scope&gt;

&lt;/dependency&gt;

&lt;dependency&gt;
 &lt;groupId&gt;commons-validator&lt;/groupId&gt;
 &lt;artifactId&gt;commons-validator&lt;/artifactId&gt;
 &lt;version&gt;1.6&lt;/version&gt;
&lt;/dependency&gt; 
</code></pre>

These are the Maven dependencies. We use Apache Commons library to validate URL strings.

<pre><code>package com.zetcode.web;

import com.zetcode.service.WebPageReader;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(name = "ReadWebPage", urlPatterns = {"/ReadWebPage"})
public class ReadWebpage extends HttpServlet {

 @Override
 protected void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 response.setContentType("text/plain;charset=UTF-8");

 String page = request.getParameter("webpage");

 String content = new WebPageReader().setWebPageName(page).getWebPageContent();

 ServletOutputStream os = response.getOutputStream();
 os.write(content.getBytes(StandardCharsets.UTF_8));
 }
}
</code></pre>

The <code>ReadWebPage</code> servlet reads the contents of the given web page and sends it back to the client in plain text format. The task of reading the page is delegated to <code>WebPageReader</code>.

<pre><code>package com.zetcode.service;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.stream.Collectors;
import org.apache.commons.validator.routines.UrlValidator;

public class WebPageReader {

 private String webpage;
 private String content;

 public WebPageReader setWebPageName(String name) {

 webpage = name;
 return this;
 }

 public String getWebPageContent() {

 try {

 boolean valid = validateUrl(webpage);

 if (!valid) {

 content = "Invalid URL; use http(s)://www.example.com format";
 return content;
 }

 URL url = new URL(webpage);

 try (InputStream is = url.openStream();
 BufferedReader br = new BufferedReader(
 new InputStreamReader(is, StandardCharsets.UTF_8))) {

 content = br.lines().collect(
 Collectors.joining(System.lineSeparator()));
 }

 } catch (IOException ex) {

 content = String.format("Cannot read webpage %s", ex);
 Logger.getLogger(WebPageReader.class.getName()).log(Level.SEVERE, null, ex);
 }

 return content;
 }

 private boolean validateUrl(String webpage) {

 UrlValidator urlValidator = new UrlValidator();

 return urlValidator.isValid(webpage);
 }
}
</code></pre>

<code>WebPageReader</code> validates the URL and reads the contents of the web page. 
It returns a string containing the HTML code of the page.

<pre><code>&lt;!DOCTYPE html&gt;
&lt;html&gt;
 &lt;head&gt;
 &lt;title&gt;Home page&lt;/title&gt;
 &lt;meta charset="UTF-8"&gt;
 &lt;/head&gt;
 &lt;body&gt;
 &lt;form action="ReadWebPage"&gt;

 &lt;label for="page"&gt;Enter a web page name:&lt;/label&gt;
 &lt;input type="text" id="page" name="webpage"&gt;

 &lt;button type="submit"&gt;Submit&lt;/button&gt;

 &lt;/form&gt;
 &lt;/body&gt;
&lt;/html&gt;
</code></pre>

Finally, this is the home page containing the HTML form. 
This is taken from my <a href="http://zetcode.com/articles/javaservletreadwebpage/" rel="nofollow noreferrer">tutorial</a> about this topic.

How do I get an InputStream from a URL?

for example, I want to take the file at the url <code>wwww.somewebsite.com/a.txt</code> and read it as an InputStream in Java, through a servlet.

I've tried

<pre><code>InputStream is = new FileInputStream("wwww.somewebsite.com/a.txt");
</code></pre>

but what I got was an error:

<pre><code>java.io.FileNotFoundException
</code></pre>

InputStream from a URL

文件系统

如何从URL中获取InputStream？例如，我希望获取url中的文件，并通过wwww.somewebsite.com/a.txt将其作为InputStream读取。我试过了InputStream is = new FileInputStream("wwww.somewebsite.com/a.txt");但我得到的...

问来自URL的InputStream
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