Java网络编程URL和URI

获得URL的方法

URI.toURL()
File.toURL()
ClassLoader.getSystemResource(String name)
Applet.getDocumentBase()

URL有以下5部分组成
http://www.ibiblio.org/javafaq/books/jnp/index.html?isbn=12345#toc
协议，也称模式 http
授权机构 www.ibiblio.org
路径 javafaq/books/jnp/index.html
查询字符串 isbn=12345
片段标识符，也成为段或ref toc
授权机构可被进一步分为用户信息(包含口令)、主机、端口
admin:[e-mail]:8080

URL编码解码
URLEncoder不会去判断这些字符如何用于URL，比如 = & 表示查询参数，因此必须将URL逐部分进行编码
URLDecoder不涉及非转义字符，所以可以传递整个URL，而不用将其分解。

public class URLEncoderExample {
  public static void main(String[] args) throws UnsupportedEncodingException {
    String input = "http://www.altavista.com/cgi-bin/query?pg=q&kl=XX&stype=stext&q=+\"Java Network Programming\"";
    System.out.println(input);
    String output = URLEncoder.encode(input, "utf-8");
    System.out.println(output);
    String s = URLEncoder.encode("http", "utf-8");
    s += "://";
    s += URLEncoder.encode("www.altavista.com", "utf-8");
    s += "/";
    s += URLEncoder.encode("cgi-bin", "utf-8");
    s += "/";
    s += URLEncoder.encode("query", "utf-8");
    s += "?";
    s += URLEncoder.encode("pg", "utf-8");
    s += "=";
    s += URLEncoder.encode("q", "utf-8");
    s += "&";
    s += URLEncoder.encode("kl", "utf-8");
    s += "=";
    s += URLEncoder.encode("XX", "utf-8");
    s += "&";
    s += URLEncoder.encode("stype", "utf-8");
    s += "=";
    s += URLEncoder.encode("stext", "utf-8");
    s += "&";
    s += URLEncoder.encode("q", "utf-8");
    s += "=";
    s += URLEncoder.encode("\"Java Network Programming\"", "utf-8");
    System.out.println(s);
  }
}

URL和URI
URL对象是从网络获取的应用程序协议的表示，而URI对象纯粹是可以解析和操作的字符串。
URI没有网络获取功能，URL有字符串解析方法getFile() getRef()，处理URL返回的字符串，分解为各个部分。

// URLSplitter
try {
  URL u = new URL("http://xace:[e-mail]/javafaq/books/jnp/index.html?isbn=12345#toc");
  System.out.println("The URL is " + u);
  System.out.println("The scheme/protocol is " + u.getProtocol());
  System.out.println("The user info is " + u.getUserInfo());
  String host = u.getHost();
  if (host != null) {
    int atSign = host.indexOf('@');
    if (atSign != -1)
      host = host.substring(atSign + 1);
    System.out.println("The host is " + host);
  } else {
    System.out.println("The host is null.");
  }
  System.out.println("The port is " + u.getPort());
  System.out.println("The defaultPort is " + u.getDefaultPort());
  System.out.println("The path is " + u.getPath());
  System.out.println("The file is " + u.getFile());
  System.out.println("The ref is " + u.getRef());
  System.out.println("The query string is " + u.getQuery());
  System.out.println("The authority is:" + u.getAuthority());
    } catch (MalformedURLException ex) {
  System.err.println("is not a URL I understand.");
}

// URISplitter
try {
  URI u = new URI("http://xace:[e-mail]/javafaq/books/jnp/index.html?isbn=12345#toc");
  System.out.println("The URI is " + u);
  if (u.isOpaque()) {
    System.out.println("This is an opaque URI.");
    System.out.println("The scheme is " + u.getScheme());
    System.out.println("The scheme specific part is " + u.getSchemeSpecificPart());
    System.out.println("The fragment ID is " + u.getFragment());
  } else {
    System.out.println("This is a hierarchical URI.");
    System.out.println("The scheme is " + u.getScheme());
    try {
      u = u.parseServerAuthority();
      System.out.println("The host is " + u.getUserInfo());
      System.out.println("The user info is " + u.getUserInfo());
      System.out.println("The port is " + u.getPort());
    } catch (URISyntaxException ex) {
      System.out.println("The authority is " + u.getAuthority());
    }
    System.out.println("The path is " + u.getPath());
    System.out.println("The query string is " + u.getQuery());
    System.out.println("The fragment ID is " + u.getFragment());
  } 
} catch (URISyntaxException ex) {
  System.err.println(" does not seem to be a URI.");
}

URI的各部分
模式、模式的有部分、片段标识符
scheme:scheme-specific-part:fragment

代理
设置HTTP代理

// java.oreilly.com和xml.oreilly.com，不使用代理
System.setProperty("http.proxyHost", "192.168.5.1");
System.setProperty("http.proxyPort", "9000");
System.setProperty("http.nonProxyHosts", "java.oreilly.com|xml.oreilly.com");

java -Dhttp.proxyHost=192.168.5.1 -Dhttp.proxyPort=9000 -Dhttp.nonProxyHosts=*.oreilly.com aaa.bbb.Class
相应的有FTP代理和Socks代理，但是Socks代理不能设置nonProxyHosts

Proxy类 ProxySelector类

cookie
Java1.5之前，只能通过直接操作HTTP首部来设置cookie，
Set-Cookie: user=xace
新版本的cookie规范，在“name=value”对后，需要一个版本属性，还允许将cookie值引号引起来，这样在引号中可以包含空格
Set-Cookie2: food="chocolate ice cream"; Version=1
当相同服务器请求同一文档时，客户端在发送给服务器的请求的Cookie首部字段中回显次cookie，
Cookie: user=xace
Cookie: $Version=1; food="chocolate ice cream"
客户端的任务就是记住收到的所有cookie，在适当的时候将正确的cookie发送给最初的服务器。
但是这有些复杂，因为cookie有一些表示属性
过期时间 Expires=Wed, 21-Dec-2010 15:23:00 GMT Max-Age=3600
路径 Path=/blog
域 Domain=.iteye.com
端口 Port="80 8080"
安全性选项 secure
这些属性往服务器回传时，均要加上$Expires $Path