JavaではHttp Proxyを使用しています。

You have to set the follwing properties：

http.proxyHost (default: <none>)http.proxyPort (default: 80 if http.proxyHost specified)http.nonProxyHosts (default: <none>)

NOTE：proxyHost、proxyPort are deprecated.you have to prefix them with「http.」.NOTE：Those properties are documented here：http://java.sun.com/javase/6/docs/technotes/guides/net/properties.html.
You can set the required properties when starting the JVM for a JAVA aplication from the command line:

java  -Dhttp.proxyHost=myproxyserver.com  -Dhttp.proxyPort=80 MyJavaApp

Or in your source：

System.setProperty("http.proxyHost", "myProxyServer.com");System.setProperty("http.proxyPort", "80");

Since Java 1.5 you can also pass a java.net.Proxy instance to the openConnection()method:

//Proxy instance, proxy ip = 123.0.0.1 with port 8080Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("123.0.0.1", 8080));URL url = new URL("http://www.yahoo.com");HttpURLConnection uc = (HttpURLConnection)url.openConnection(proxy);uc.connect();        String page;StringBuffer tmp = new StringBuffer();BufferedReader in = new BufferedReader(new InputStreamReader(uc.getInputStream()));while ((line = in.readLine()) != null){   page.append(line + "
");}System.out.println(page);

so you don't need to set system properties.
You can use the default PROXY as defined by your networking settings.

System.setProperty("java.net.useSystemProxies", "true");List l = null;try {  l = ProxySelector.getDefault().select(new URI("http://www.yahoo.com"));}catch (URISyntaxException e) {  e.printStackTrace();}if (l != null) {   for (Iterator iter = l.iterator(); iter.hasNext() {      java.net.Proxy proxy = (java.net.Proxy) iter.next();      System.out.println("proxy hostname : " + proxy.type());      InetSocketAddress addr = (InetSocketAddress) proxy.address();      if (addr == null) {        System.out.println("No Proxy");      }       else {        System.out.println("proxy hostname : " + addr.getHostName());        System.out.println("proxy port : " + addr.getPort());      }   }}

To bypass the PROXY、

URL url = new URL("http://internal.server.local/");URLConnection conn = url.openConnection(Proxy.NO_PROXY);

Proxy and Username/Password
You might need to identify yourself to the proxy server.
One way is to use the HTTP property「Proxy-Authorization」with a username：password base 64 encoded.

System.setProperty("http.proxyHost", "myProxyServer.com");System.setProperty("http.proxyPort", "80");URL url=new URL("http://someserver/somepage");URLConnection uc = url.openConnection ();String encoded = new String      (Base64.base64Encode(new String("username:password").getBytes()));uc.setRequestProperty("Proxy-Authorization", "Basic " + encoded);uc.connect();

NOTE：For a base 64 function、see this How-to.
The follwing example dumps the content of a URL but before we identify ourself to the proxy.

import java.net.*;import java.io.*;public class URLUtils {  public static void main(String s[]) {    URLUtils.dump("http://www.yahoo.com");    System.out.println("**************");    URLUtils.dump("https://www.paypal.com");    System.out.println("**************");  }  public static void dump(String URLName){    try {      DataInputStream di = null;      FileOutputStream fo = null;      byte [] b = new byte[1];      // PROXY      System.setProperty("http.proxyHost","proxy.mydomain.local") ;      System.setProperty("http.proxyPort", "80") ;      URL u = new URL(URLName);      HttpURLConnection con = (HttpURLConnection) u.openConnection();      //      // it's not the greatest idea to use a sun.misc.* class      // Sun strongly advises not to use them since they can      // change or go away in a future release so beware.      //      sun.misc.BASE64Encoder encoder = new sun.misc.BASE64Encoder();      String encodedUserPwd =         encoder.encode("mydomain\\MYUSER:MYPASSWORD".getBytes());      con.setRequestProperty         ("Proxy-Authorization", "Basic " + encodedUserPwd);      // PROXY ----------      di = new DataInputStream(con.getInputStream());      while(-1 != di.read(b,0,1)) {         System.out.print(new String(b));      }    }    catch (Exception e) {      e.printStackTrace();    }  }}

With JDK 1.2、the java.net.Authenticator can be used to send the credntials when need.

public static void dump(String URLName){  try {    DataInputStream di = null;    FileOutputStream fo = null;    byte [] b = new byte[1];     // PROXY    System.setProperty("http.proxyHost","proxy.mydomain.local") ;    System.setProperty("http.proxyPort", "80") ;     Authenticator.setDefault(new Authenticator() {      protected PasswordAuthentication getPasswordAuthentication() {        return new           PasswordAuthentication("mydomain\\username","password".toCharArray());    }});     URL u = new URL(URLName);    HttpURLConnection con = (HttpURLConnection) u.openConnection();    di = new DataInputStream(con.getInputStream());    while(-1 != di.read(b,0,1)) {       System.out.print(new String(b));    }  }  catch (Exception e) {          e.printStackTrace();  }}

Bypa Proxy
In intranet environment，you may need to bypass the proxy server and go directly to the http server.
The http.nonProxyHosts property indicates the hosts shatch shoud be connected too directly and not through the proxy server.The value can be a list of hosts，each seperated bya|

java.exe     -Dhttp.nonProxyHosts="*.mycompany.com|*.mycompany.local|localhost"       MyClass