URLs
URL class ใช้รับข้อมูลจากระบบเครือข่าย ไม่จำเป็นต้องสนใจรายละเอียดภายใน ต้อง import java.net.URL ถ้าเกิดข้อผิดพลาดจะ thows MalformedURLException ตัวอย่าง เช่น or ftp://ftp.redhat.com/pub/ ftp://ftp.redhat.com/pub/ftp://ftp.redhat.com/pub/
Creating New URLs Constructing a URL from a string public URL(String url) public URL(String url) try { try { URL u = new URL(" URL u = new URL(" } catch (MalformedURLException ex) { catch (MalformedURLException ex) { System.err.println(ex); System.err.println(ex); }
ProtocolTester private static void testProtocol(String url) { try { URL u = new URL(url); System.out.println(u.getProtocol( ) + " is supported"); } catch (MalformedURLException ex) { String protocol = url.substring(0, url.indexOf(':')); System.out.println(protocol + " is not supported"); }
ProtocolTester import java.net.*; public class protocolTester { public static void main(String[] args) { // hypertext transfer protocol testProtocol(" // secure http testProtocol(" // file transfer protocol testProtocol("ftp://metalab.unc.edu/pub/languages/java/javafaq/"); // Simple Mail Transfer Protocol // telnet testProtocol("telnet://dibner.poly.edu/"); // local file access testProtocol("file:///etc/passwd"); // gopher testProtocol("gopher://gopher.anc.org.za/"); // Lightweight Directory Access Protocol testProtocol( "ldap://ldap.itd.umich.edu/o=University%20of%20Michigan,c=US?postalAddress");
ProtocolTester // JAR testProtocol( "jar: +"/com/macfaq/io/StreamCopier.class"); // NFS, Network File System testProtocol("nfs://utopia.poly.edu/usr/tmp/"); // a custom protocol for JDBC testProtocol("jdbc:mysql://luna.metalab.unc.edu:3306/NEWS"); // rmi, a custom protocol for remote method invocation testProtocol("rmi://metalab.unc.edu/RenderEngine"); // custom protocols for HotJava testProtocol("doc:/UsersGuide/release.html"); testProtocol("netdoc:/UsersGuide/release.html"); testProtocol("systemresource:// testProtocol("verbatim: }
ProtocolTester ผลลัพธ์ http is supported https is supported ftp is supported mailto is supported telnet is not supported file is supported gopher is supported ldap is not supported jar is supported nfs is not supported jdbc is not supported rmi is not supported doc is supported netdoc is supported systemresource is supported verbatim is supported Press any key to continue...
Constructing a URL from its component parts ประกอบด้วยส่วนประกอบ 3 ส่วน Protocol Protocol HostName HostName File File public URL(String protocol, String hostname, String file) เช่น try { URL u = new URL("http", " "/blueribbon.html#intro"); } catch (MalformedURLException ex) { }
Constructing a URL from its component parts เพิ่ม Port ที่ใช้งาน public URL(String protocol, String host, int port, String file) try { URL u = new URL("http", "fourier.dur.ac.uk", 8000, "/~dma3mjh/jsci/"); } catch (MalformedURLException ex) { System.err.println(ex); }
public String getHost( ) ทำการ Return HostName URL u = new String host = u.getHost( ); return wuarchive.wustl.edu
public int getPort( ) Return Port number โดยที่ ถ้าไม่ระบุ Port ใน URL จะ return -1 ออกมา URL u = new URL(" System.out.println("The port part of " + u + " is " + u.getPort( )); ผลลัพธ์ The port part of is -1 หรือระบุ Port URL u = new URL(" System.out.println("The port part of " + u + " is " + u.getPort( )); ผลลัพธ์ The port part of is 80
public int getDefaultPort( ) Return Port number ที่ใช้ใน URL โดยจะ Return หมายเลข Port ที่ใช้ใน URL URL u = new URL(" System.out.println("The port part of " + u + " is " + u.getDefaultPort()); ผลลัพธ์ The port part of is 80
public String getFile( ) ทำการคืน Path และชื่อ File ที่อยู่ใน URL ถ้าไม่ระบุก็ จะคืน Emtry String URL u = new URL(" ontent&task=blogsection&id=11&Itemid=40"); System.out.println(u.getFile()); ผลลัพธ์ /main/index.php?option=com_content&task=blogsection&i d=11&Itemid=40
public String getPath( ) ทำการคืน Path และชื่อ File ที่อยู่ใน URL ไม่ร่วม query string ใน URL URL u = new URL(" content&task=blogsection&id=11&Itemid=40"); System.out.println(u.getPath()); ผลลัพธ์ /main/index.php
public String getQuery( ) คืนค่า query string ของ URL ถ้าไม่มีจะคืนค่า Null URL u = new URL(" sk=blogsection&id=11&Itemid=40"); System.out.println(u.getQuery()); ผลลัพธ์ option=com_content&task=blogsection&id=11&Itemid=40
Retrieving Data from a URL รับข้อมูลจาก URL public InputStream openStream( ) throws IOException public URLConnection openConnection( ) throws IOException public URLConnection openConnection(Proxy proxy) throws IOException // 1.5 public Object getContent( ) throws IOException public Object getContent(Class[] classes) throws IOException // 1.3
public InputStream openStream( ) throws IOException รับข้อมูลจาก Server โดยผ่าน URL อ่านข้อมูลผ่าน InputStream try { URL u = new URL(" InputStream in = u.openStream( ); int c; while ((c = in.read( )) != -1) System.out.write(c); } catch (IOException ex) { System.err.println(ex); }
public InputStream openStream( ) import java.net.*; import java.io.*; public class sourceViewer { public static void main (String[] args) { String hostName=" try { //Open the URL for reading URL u = new URL(hostName); InputStream in = u.openStream(); // buffer the input to increase performance in = new BufferedInputStream(in); // chain the InputStream to a Reader Reader r = new InputStreamReader(in); int c; while ((c = r.read( )) != -1) { System.out.print((char) c); } catch (MalformedURLException ex) { System.err.println(hostName + " is not a parseable URL"); } catch (IOException ex) { System.err.println(ex); } } // end main } // end SourceViewer ตัวอย่างโปรแกรมรับข้อมูล HTML
public URLConnection openConnection( ) Return URLConnection Object สามารถ เข้า ถึงข้อมูลต่างๆได้โดยผ่าน URLConnection try { URL u = new URL(" try { URLConnection uc = u.openConnection( ); InputStream in = uc.getInputStream( ); // read from the connection... } // end try catch (IOException ex) { System.err.println(ex); } } // end try catch (MalformedURLException ex) { System.err.println(ex); }
public final Object getContent( ) ทำหน้าที่โหลดข้อมูลมาจาก URL ที่ระบุ ถ้าข้อมูลเป็น text ก็ใช้ InputStream รับข้อมูล ถ้าข้อมูลเป็น รูปภาพ ก็ใช้ java.awt.ImageProducer รับข้อมูล try { URL u = new URL(" Object o = u.getContent( ); // cast the Object to the appropriate type // work with the Object... } catch (Exception ex) { System.err.println(ex); }
getContent( ) import java.net.*; import java.io.*; public class ContentGetter { public static void main (String[] args) { String HostName=" String HostName=" //Open the URL for reading try { URL u = new URL(HostName); try { Object o = u.getContent( ); System.out.println("I got a " + o.getClass( ).getName( )); } // end try catch (IOException ex) { System.err.println(ex); } } // end try catch (MalformedURLException ex) { System.err.println(HostName + " is not a parseable URL"); } } // end main } // end ContentGetter ผลลัพธ์ :I got a sun.net.
getContent( ) ถ้า HostName=“ hics_new/animation.gif” ผลลัพธ์ I got a sun.awt.image.URLImageSource
public final Object getContent(Class[] classes) กำหนดชนิดข้อมูลที่รับมาจาก Server ใน อาร์เรย์ classes ใช้การตรวจสอบ ชนิดของ class โดยใช้ instanceof URL u = new URL(" Class[] types = new Class[3]; types[0] = String.class; types[1] = Reader.class; types[2] = InputStream.class; Object o = u.getContent(types);
public final Object getContent(Class[] classes) if (o instanceof String) { System.out.println(o); } else if (o instanceof Reader) { int c; Reader r = (Reader) o; while ((c = r.read( )) != -1) System.out.print((char) c); } else if (o instanceof InputStream) { int c; InputStream in = (InputStream) o; while ((c = in.read( )) != -1) System.out.write(c); } else { System.out.println("Error: unexpected type " + o.getClass( )); }
URLEncoder () ทำการ Encode / & # ; $ + = and % ใน URL รูปแบบ public static String encode(String s) public static String encode(String s, String encoding) throws UnsupportedEncodingException
URLEncoder () import java.net.URLEncoder; import java.io.UnsupportedEncodingException; public class EncoderTest { public static void main(String[] args) { try { System.out.println(URLEncoder.encode("This string has spaces","UTF-8")); System.out.println(URLEncoder.encode("This*string*has*asterisks","UTF-8")); System.out.println(URLEncoder.encode("This%string%has%percent%signs","UTF-8")); System.out.println(URLEncoder.encode("This+string+has+pluses","UTF-8")); System.out.println(URLEncoder.encode("This/string/has/slashes","UTF-8")); System.out.println(URLEncoder.encode("This\"string\"has\"quote\"marks","UTF-8")); System.out.println(URLEncoder.encode("This:string:has:colons","UTF-8")); System.out.println(URLEncoder.encode("This~string~has~tildes","UTF-8")); System.out.println(URLEncoder.encode("This(string)has(parentheses)","UTF-8")); System.out.println(URLEncoder.encode("This.string.has.periods","UTF-8")); System.out.println(URLEncoder.encode("This=string=has=equals=signs","UTF-8")); System.out.println(URLEncoder.encode("This&string&has&ersands","UTF-8")); System.out.println(URLEncoder.encode("This?string?has?non-ASCII characters", "UTF-8")); } catch (UnsupportedEncodingException ex) { throw new RuntimeException("Broken VM does not support UTF-8"); }
URLEncoder () ผลลัพธ์ This+string+has+spaces This*string*has*asterisks This%25string%25has%25percent%25signs This%2Bstring%2Bhas%2Bpluses This%2Fstring%2Fhas%2Fslashes This%22string%22has%22quote%22marks This%3Astring%3Ahas%3Acolons This%7Estring%7Ehas%7Etildes This%28string%29has%28parentheses%29 This.string.has.periods This%3Dstring%3Dhas%3Dequals%3Dsigns This%26string%26has%26ampersands This%C3%A9string%C3%A9has%C3%A9non-ASCII+characters
URLDecoder ทำหน้าที่แปลงข้อมูลกลับจากการเข้ารหัส public static String decode(String s) throws Exception public static String decode(String s, String encoding) // Java 1.4 throws UnsupportedEncodingException String enC =URLEncoder.encode("This string has spaces","UTF-8"); System.out.print(enC); System.out.println(URLDecoder.decode(enC,"UTF-8")); This+string+has+spaces ผลลัพธ์ This+string+has+spaces This string has spaces