Package java.net

提供实现网络应用程序的类。

See: 描述

接口摘要

接口	描述
ContentHandlerFactory	该界面为内容处理程序定义了一个工厂。
CookiePolicy	CookiePolicy实现决定哪些Cookie应该被接受，哪些应该被拒绝。
CookieStore	CookieStore对象表示Cookie的存储。
DatagramSocketImplFactory	该接口为数据报套接字实现定义了一个工厂。
FileNameMap	一个简单的界面，提供了一种在文件名和MIME类型字符串之间映射的机制。
ProtocolFamily	代表一系列通信协议。
SocketImplFactory	该接口定义了一个用于套接字实现的工厂。
SocketOption<T>	与套接字关联的套接字选项。
SocketOptions	获取/设置套接字选项的方法的接口。
URLStreamHandlerFactory	该接口为 URL流协议处理程序定义了一个工厂。

类摘要

类	描述
Authenticator	Authenticator类代表一个知道如何获取网络连接认证的对象。
CacheRequest	表示在ResponseCache中存储资源的通道。
CacheResponse	代表从ResponseCache中检索资源的通道。
ContentHandler	抽象类 ContentHandler是读取所有类的超 Object从 URLConnection 。
CookieHandler	CookieHandler对象提供一个回调机制，将HTTP状态管理策略实现连接到HTTP协议处理程序中。
CookieManager	CookieManager提供了一个具体的CookieHandler 实现 ，它将cookie的存储与接受和拒绝cookie的策略分开。
DatagramPacket	该类表示数据报包。
DatagramSocket	此类表示用于发送和接收数据报数据包的套接字。
DatagramSocketImpl	抽象数据报和组播套接字实现基类。
HttpCookie	HttpCookie对象表示HTTP cookie，它承载服务器和用户代理之间的状态信息。
HttpURLConnection	支持HTTP特定功能的URLConnection。
IDN	提供在正常Unicode表示和ASCII兼容编码（ACE）表示之间转换国际化域名（IDN）的方法。
Inet4Address	该类表示Internet协议版本4（IPv4）地址。
Inet6Address	该类表示Internet协议版本6（IPv6）地址。
InetAddress	此类表示Internet协议（IP）地址。
InetSocketAddress	该类实现IP套接字地址（IP地址+端口号）它也可以是一对（主机名+端口号），在这种情况下将尝试解析主机名。
InterfaceAddress	此类表示网络接口地址。
JarURLConnection	与Java ARchive（JAR）文件或JAR文件中的条目的URL连接。
MulticastSocket	组播数据报套接字类对发送和接收IP组播数据包很有用。
NetPermission	此类用于各种网络权限。
NetworkInterface	此类表示由名称组成的网络接口和分配给此接口的IP地址列表。
PasswordAuthentication	PasswordAuthentication类是Authenticator使用的数据持有者。
Proxy	此类表示代理设置，通常是类型（http，socks）和套接字地址。
ProxySelector	选择在连接到URL引用的网络资源时使用的代理服务器（如果有）。
ResponseCache	表示URLConnection缓存的实现。
SecureCacheResponse	表示最初通过安全手段（例如TLS）检索的缓存响应。
ServerSocket	这个类实现了服务器套接字。
Socket	该类实现客户端套接字（也称为“套接字”）。
SocketAddress	这个类代表一个没有协议附件的Socket地址。
SocketImpl	抽象类 SocketImpl是实际实现套接字的所有类的公共超类。
SocketPermission	此类表示通过套接字访问网络。
StandardSocketOptions	定义 标准套接字选项。
URI	表示统一资源标识符（URI）参考。
URL	URL类 URL统一资源定位器，指向万维网上的“资源”的指针。
URLClassLoader	此类加载器用于从引用JAR文件和目录的URL的搜索路径加载类和资源。
URLConnection	抽象类 URLConnection是表示应用程序和URL之间的通信链接的所有类的超类。
URLDecoder	HTML表单解码的实用类。
URLEncoder	HTML表单编码的实用类。
URLPermission	表示访问由给定网址定义的资源或资源集的权限，以及给定的用户可设置请求方法和请求标头集合的权限。
URLStreamHandler	抽象类 URLStreamHandler是所有流协议处理程序的通用超类。

枚举摘要

Enum	描述
Authenticator.RequestorType	请求认证的实体的类型。
Proxy.Type	代表代理类型。
StandardProtocolFamily	定义通信协议的标准系列。

异常摘要

异常	描述
BindException	指示尝试将套接字绑定到本地地址和端口时发生错误。
ConnectException	指示尝试将套接字连接到远程地址和端口时发生错误。
HttpRetryException	抛出表示HTTP请求需要重试，但由于启用了流式传输模式，因此无法自动重试。
MalformedURLException	抛出以表示发生格式不正确的网址。
NoRouteToHostException	指示尝试将套接字连接到远程地址和端口时发生错误。
PortUnreachableException	指示在连接的数据报上收到了ICMP端口不可达消息。
ProtocolException	抛出以表示底层协议有错误，如TCP错误。
SocketException	抛出以表示创建或访问Socket时出错。
SocketTimeoutException	指示在套接字上发生超时时读取或接受。
UnknownHostException	抛出以表示无法确定主机的IP地址。
UnknownServiceException	抛出以表示发生未知服务异常。
URISyntaxException	检查的异常抛出以指示不能将字符串解析为URI引用。

Package java.net Description

Provides the classes for implementing networking applications.

The java.net package can be roughly divided in two sections:

• A Low Level API, which deals with the following abstractions:

  • Addresses, which are networking identifiers, like IP addresses.

  • Sockets, which are basic bidirectional data communication mechanisms.

  • Interfaces, which describe network interfaces.

• A High Level API, which deals with the following abstractions:

  • URIs, which represent Universal Resource Identifiers.

  • URLs, which represent Universal Resource Locators.

  • Connections, which represents connections to the resource pointed to by URLs.

Addresses

Addresses are used throughout the java.net APIs as either host identifiers, or socket endpoint identifiers.

The InetAddress class is the abstraction representing an IP (Internet Protocol) address. It has two subclasses:

• Inet4Address for IPv4 addresses.
• Inet6Address for IPv6 addresses.

But, in most cases, there is no need to deal directly with the subclasses, as the InetAddress abstraction should cover most of the needed functionality.

About IPv6

Not all systems have support for the IPv6 protocol, and while the Java networking stack will attempt to detect it and use it transparently when available, it is also possible to disable its use with a system property. In the case where IPv6 is not available, or explicitly disabled, Inet6Address are not valid arguments for most networking operations any more. While methods like InetAddress.getByName(java.lang.String) are guaranteed not to return an Inet6Address when looking up host names, it is possible, by passing literals, to create such an object. In which case, most methods, when called with an Inet6Address will throw an Exception.

Sockets

Sockets are means to establish a communication link between machines over the network. The java.net package provides 4 kinds of Sockets:

• Socket is a TCP client API, and will typically be used to connect to a remote host.
• ServerSocket is a TCP server API, and will typically accept connections from client sockets.
• DatagramSocket is a UDP endpoint API and is used to send and receive datagram packets.
• MulticastSocket is a subclass of DatagramSocket used when dealing with multicast groups.

Sending and receiving with TCP sockets is done through InputStreams and OutputStreams which can be obtained via the Socket.getInputStream() and Socket.getOutputStream() methods.

Interfaces

The NetworkInterface class provides APIs to browse and query all the networking interfaces (e.g. ethernet connection or PPP endpoint) of the local machine. It is through that class that you can check if any of the local interfaces is configured to support IPv6.

Note, all conforming implementations must support at least one NetworkInterface object, which must either be connected to a network, or be a "loopback" interface that can only communicate with entities on the same machine.

High level API

A number of classes in the java.net package do provide for a much higher level of abstraction and allow for easy access to resources on the network. The classes are:

• URI is the class representing a Universal Resource Identifier, as specified in RFC 2396. As the name indicates, this is just an Identifier and doesn't provide directly the means to access the resource.
• URL is the class representing a Universal Resource Locator, which is both an older concept for URIs and a means to access the resources.
• URLConnection is created from a URL and is the communication link used to access the resource pointed by the URL. This abstract class will delegate most of the work to the underlying protocol handlers like http or https.
• HttpURLConnection is a subclass of URLConnection and provides some additional functionalities specific to the HTTP protocol.

The recommended usage is to use URI to identify resources, then convert it into a URL when it is time to access the resource. From that URL, you can either get the URLConnection for fine control, or get directly the InputStream.

Here is an example:

URI uri = new URI("http://java.sun.com/");
 URL url = uri.toURL();
 InputStream in = url.openStream();

Protocol Handlers

As mentioned, URL and URLConnection rely on protocol handlers which must be present, otherwise an Exception is thrown. This is the major difference with URIs which only identify resources, and therefore don't need to have access to the protocol handler. So, while it is possible to create an URI with any kind of protocol scheme (e.g. myproto://myhost.mydomain/resource/), a similar URL will try to instantiate the handler for the specified protocol; if it doesn't exist an exception will be thrown.

By default the protocol handlers are loaded dynamically from the default location. It is, however, possible to add to the search path by setting the java.protocol.handler.pkgs system property. For instance if it is set to myapp.protocols, then the URL code will try, in the case of http, first to load myapp.protocols.http.Handler, then, if this fails, http.Handler from the default location.

Note that the Handler class has to be a subclass of the abstract class URLStreamHandler.

Additional Specification

• Networking System Properties

从以下版本开始：

JDK1.0