InputStream from a URL

Question

How do I get an InputStream from a URL   for example  I want to take the file at the url wwww somewebsite com a txt and read it as an InputStream in Java  through a servlet   I ve tried  InputStream is   new FileInputStream  wwww somewebsite com a txt      but what I got was an error   java io FileNotFoundException

User · Answer

Try   final InputStream is   new URL  http   wwww somewebsite com a txt   openStream

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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

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a  wwww somewebsite com a txt isn t a  file URL   It isn t a URL at all  If you put http    on the front of it it would be an HTTP URL  which is clearly what you intend here    b  FileInputStream is for files  not URLs    c  The way to get an input stream from any URL is via URL openStream    or URL getConnection   getInputStream    which is equivalent but you might have other reasons to get the URLConnection and play with it first

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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 InputStream classes  but it could be done more easily with JSoup library    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      These are the Maven dependencies  We use Apache Commons library to validate URL strings   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              The ReadWebPage 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 WebPageReader   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             WebPageReader validates the URL and reads the contents of the web page   It returns a string containing the HTML code of the page    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    Finally  this is the home page containing the HTML form   This is taken from my tutorial about this topic

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Pure Java    urlToInputStream url httpHeaders     With some success I use this method  It handles redirects and one can pass a variable number of HTTP headers asMap lt String String gt   It also allows redirects from HTTP to HTTPS    private InputStream urlToInputStream URL url  Map lt String  String gt  args        HttpURLConnection con   null      InputStream inputStream   null      try           con    HttpURLConnection  url openConnection            con setConnectTimeout 15000           con setReadTimeout 15000           if  args    null                for  Entry lt String  String gt  e   args entrySet                      con setRequestProperty e getKey    e getValue                                     con connect            int responseCode   con getResponseCode               By default the connection will follow redirects  The following            block is only entered if the implementation of HttpURLConnection            does not perform the redirect  The exact behavior depends to             the actual implementation  e g  sun net                  Attention  This block allows the connection to             switch protocols  e g  HTTP to HTTPS   which is  lt b gt not lt  b gt              default behavior  See  https   stackoverflow com questions 1884230             for more info                        if  responseCode  lt  400  amp  amp  responseCode  gt  299                String redirectUrl   con getHeaderField  Location                try                   URL newUrl   new URL redirectUrl                   return urlToInputStream newUrl  args                 catch  MalformedURLException e                    URL newUrl   new URL url getProtocol             url getHost     redirectUrl                   return urlToInputStream newUrl  args                                                      inputStream   con getInputStream            return inputStream        catch  Exception e            throw new RuntimeException e             Full example call  private InputStream getInputStreamFromUrl URL url  String user  String passwd  throws IOException           String encoded   Base64 getEncoder   encodeToString  user         passwd  getBytes StandardCharsets UTF 8            Map lt String String gt  httpHeaders new Map lt  gt             httpHeaders put  Accept    application json            httpHeaders put  User-Agent    myApplication            httpHeaders put  Authorization    Basic     encoded           return urlToInputStream url httpHeaders

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Use java net URL openStream   with a proper URL  including the protocol    E g   InputStream input   new URL  http   www somewebsite com a txt   openStream             See also    Using java net URLConnection to fire and handle HTTP requests

[java] InputStream from a URL

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