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 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.
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 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.
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.
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. This API has been superseded by the newer HTTP Client API.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://www.example.com/"); URL url = uri.toURL(); InputStream in = url.openStream();
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 deploy additional protocols handlers as services
. Service providers of type URLStreamHandlerProvider are located at runtime, as specified in the URL constructor.
Class | Description |
---|---|
Authenticator | The class Authenticator represents an object that knows how to obtain authentication for a network connection. |
Authenticator.RequestorType | The type of the entity requesting authentication. |
BindException | Signals that an error occurred while attempting to bind a socket to a local address and port. |
CacheRequest | Represents channels for storing resources in the ResponseCache. |
CacheResponse | Represent channels for retrieving resources from the ResponseCache. |
ConnectException | Signals that an error occurred while attempting to connect a socket to a remote address and port. |
ContentHandler | The abstract class ContentHandler is the superclass of all classes that read an Object from a URLConnection . |
ContentHandlerFactory | This interface defines a factory for content handlers. |
CookieHandler | A CookieHandler object provides a callback mechanism to hook up a HTTP state management policy implementation into the HTTP protocol handler. |
CookieManager | CookieManager provides a concrete implementation of CookieHandler , which separates the storage of cookies from the policy surrounding accepting and rejecting cookies. |
CookiePolicy | CookiePolicy implementations decide which cookies should be accepted and which should be rejected. |
CookieStore | A CookieStore object represents a storage for cookie. |
DatagramPacket | This class represents a datagram packet. |
DatagramSocket | This class represents a socket for sending and receiving datagram packets. |
DatagramSocketImpl | Abstract datagram and multicast socket implementation base class. |
DatagramSocketImplFactory | This interface defines a factory for datagram socket implementations. |
FileNameMap | A simple interface which provides a mechanism to map between a file name and a MIME type string. |
HttpCookie | An HttpCookie object represents an HTTP cookie, which carries state information between server and user agent. |
HttpRetryException | Thrown to indicate that a HTTP request needs to be retried but cannot be retried automatically, due to streaming mode being enabled. |
HttpURLConnection | A URLConnection with support for HTTP-specific features. |
IDN | Provides methods to convert internationalized domain names (IDNs) between a normal Unicode representation and an ASCII Compatible Encoding (ACE) representation. |
Inet4Address | This class represents an Internet Protocol version 4 (IPv4) address. |
Inet6Address | This class represents an Internet Protocol version 6 (IPv6) address. |
InetAddress | This class represents an Internet Protocol (IP) address. |
InetSocketAddress | This class implements an IP Socket Address (IP address + port number) It can also be a pair (hostname + port number), in which case an attempt will be made to resolve the hostname. |
InterfaceAddress | This class represents a Network Interface address. |
JarURLConnection | A URL Connection to a Java ARchive (JAR) file or an entry in a JAR file. |
MalformedURLException | Thrown to indicate that a malformed URL has occurred. |
MulticastSocket | A MulticastSocket is a datagram socket that is convenient for sending and receiving IP multicast datagrams. |
NetPermission | This class is for various network permissions. |
NetworkInterface | This class represents a Network Interface made up of a name, and a list of IP addresses assigned to this interface. |
NoRouteToHostException | Signals that an error occurred while attempting to connect a socket to a remote address and port. |
PasswordAuthentication | The class PasswordAuthentication is a data holder that is used by Authenticator. |
PortUnreachableException | Signals that an ICMP Port Unreachable message has been received on a connected datagram. |
ProtocolException | Thrown to indicate that there is an error in the underlying protocol, such as a TCP error. |
ProtocolFamily | Represents a family of communication protocols. |
Proxy | This class represents a proxy setting, typically a type (http, socks) and a socket address. |
Proxy.Type | Represents the proxy type. |
ProxySelector | Selects the proxy server to use, if any, when connecting to the network resource referenced by a URL. |
ResponseCache | Represents implementations of URLConnection caches. |
SecureCacheResponse | Represents a cache response originally retrieved through secure means, such as TLS. |
ServerSocket | This class implements server sockets. |
Socket | This class implements client sockets (also called just "sockets"). |
SocketAddress | This class represents a Socket Address with no protocol attachment. |
SocketException | Thrown to indicate that there is an error creating or accessing a Socket. |
SocketImpl | The abstract class SocketImpl is a common superclass of all classes that actually implement sockets. |
SocketImplFactory | This interface defines a factory for socket implementations. |
SocketOption<T> | A socket option associated with a socket. |
SocketOptions | Interface of methods to get/set socket options. |
SocketPermission | This class represents access to a network via sockets. |
SocketTimeoutException | Signals that a timeout has occurred on a socket read or accept. |
StandardProtocolFamily | Defines the standard families of communication protocols. |
StandardSocketOptions | Defines the standard socket options. |
UnixDomainSocketAddress | A Unix domain socket address. |
UnknownHostException | Thrown to indicate that the IP address of a host could not be determined. |
UnknownServiceException | Thrown to indicate that an unknown service exception has occurred. |
URI | Represents a Uniform Resource Identifier (URI) reference. |
URISyntaxException | Checked exception thrown to indicate that a string could not be parsed as a URI reference. |
URL | Class URL represents a Uniform Resource Locator, a pointer to a "resource" on the World Wide Web. |
URLClassLoader | This class loader is used to load classes and resources from a search path of URLs referring to both JAR files and directories. |
URLConnection | The abstract class URLConnection is the superclass of all classes that represent a communications link between the application and a URL. |
URLDecoder | Utility class for HTML form decoding. |
URLEncoder | Utility class for HTML form encoding. |
URLPermission | Represents permission to access a resource or set of resources defined by a given url, and for a given set of user-settable request methods and request headers. |
URLStreamHandler | The abstract class URLStreamHandler is the common superclass for all stream protocol handlers. |
URLStreamHandlerFactory | This interface defines a factory for URL stream protocol handlers. |
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/net/package-summary.html