# Class URLStreamHandler

java.lang.Object
java.net.URLStreamHandler

public abstract class URLStreamHandler extends Object
The abstract class `URLStreamHandler` is the common superclass for all stream protocol handlers. A stream protocol handler knows how to make a connection for a particular protocol type, such as `http` or `https`.

In most cases, an instance of a `URLStreamHandler` subclass is not created directly by an application. Rather, the first time a protocol name is encountered when constructing a `URL`, the appropriate stream protocol handler is automatically loaded.

Since:
  1.0
See Also:
  - `URL(java.lang.String, java.lang.String, int, java.lang.String)`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `URLStreamHandler()`
  Constructor for subclasses to call.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected boolean`
  `equals(URL u1, URL u2)`
  Provides the default equals calculation.
  `protected int`
  `getDefaultPort()`
  Returns the default port for a URL parsed by this handler.
  `protected InetAddress`
  `getHostAddress(URL u)`
  Get the IP address of our host.
  `protected int`
  `hashCode(URL u)`
  Provides the default hash calculation.
  `protected boolean`
  `hostsEqual(URL u1, URL u2)`
  Compares the host components of two URLs.
  `protected abstract URLConnection`
  `openConnection(URL u)`
  Opens a connection to the object referenced by the `URL` argument.
  `protected URLConnection`
  `openConnection(URL u, Proxy p)`
  Same as openConnection(URL), except that the connection will be made through the specified proxy; Protocol handlers that do not support proxying will ignore the proxy parameter and make a normal connection.
  `protected void`
  `parseURL(URL u, String spec, int start, int limit)`
  Parses the string representation of a `URL` into a `URL` object.
  `protected boolean`
  `sameFile(URL u1, URL u2)`
  Compare two urls to see whether they refer to the same file, i.e., having the same protocol, host, port, and path.
  `protected void`
  `setURL(URL u, String protocol, String host, int port, String file, String ref)`
  Deprecated.
  Use setURL(URL, String, String, int, String, String, String, String);
  `protected void`
  `setURL(URL u, String protocol, String host, int port, String authority, String userInfo, String path, String query, String ref)`
  Sets the fields of the `URL` argument to the indicated values.
  `protected String`
  `toExternalForm(URL u)`
  Converts a `URL` of a specific protocol to a `String`.

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Constructor Details

  - ### URLStreamHandler

    public URLStreamHandler()
    Constructor for subclasses to call.

- ## Method Details

  - ### openConnection

    protected abstract URLConnection openConnection(URL u) throws IOException
    Opens a connection to the object referenced by the `URL` argument. This method should be overridden by a subclass.

    If for the handler's protocol (such as HTTP or JAR), there exists a public, specialized URLConnection subclass belonging to one of the following packages or one of their subpackages: java.lang, java.io, java.util, java.net, the connection returned will be of that subclass. For example, for HTTP an HttpURLConnection will be returned, and for JAR a JarURLConnection will be returned.

    Parameters:
      `u` - the URL that this connects to.
    Returns:
      a `URLConnection` object for the `URL`.
    Throws:
      `IOException` - if an I/O error occurs while opening the connection.

  - ### openConnection

    protected URLConnection openConnection(URL u, Proxy p) throws IOException
    Same as openConnection(URL), except that the connection will be made through the specified proxy; Protocol handlers that do not support proxying will ignore the proxy parameter and make a normal connection.

    Calling this method preempts the system's default `ProxySelector` settings.

    Implementation Requirements:
      The default implementation of this method first checks that the given `URL` and `Proxy` are not null, then throws `UnsupportedOperationException`. Subclasses should override this method with an appropriate implementation.
    Parameters:
      `u` - the URL that this connects to.
      `p` - the proxy through which the connection will be made. If direct connection is desired, Proxy.NO_PROXY should be specified.
    Returns:
      a `URLConnection` object for the `URL`.
    Throws:
      `IOException` - if an I/O error occurs while opening the connection.
      `IllegalArgumentException` - if either u or p is null, or p has the wrong type.
      `UnsupportedOperationException` - if the subclass that implements the protocol doesn't support this method.
    Since:
      1.5

  - ### parseURL

    protected void parseURL(URL u, String spec, int start, int limit)
    Parses the string representation of a `URL` into a `URL` object.

    If there is any inherited context, then it has already been copied into the `URL` argument.

    The `parseURL` method of `URLStreamHandler` parses the string representation as if it were an `http` specification. Most URL protocol families have a similar parsing. A stream protocol handler for a protocol that has a different syntax must override this routine.

    Parameters:
      `u` - the `URL` to receive the result of parsing the spec.
      `spec` - the `String` representing the URL that must be parsed.
      `start` - the character index at which to begin parsing. This is just past the '`:`' (if there is one) that specifies the determination of the protocol name.
      `limit` - the character position to stop parsing at. This is the end of the string or the position of the "`#`" character, if present. All information after the sharp sign indicates an anchor.
    Throws:
      `IllegalArgumentException` - if the implementation of the protocol handler rejects any of the given parameters
      `NullPointerException` - if `u` is `null`, or if `start < limit` and `spec` is `null`

  - ### getDefaultPort

    protected int getDefaultPort()
    Returns the default port for a URL parsed by this handler. This method is meant to be overridden by handlers with default port numbers.
    Returns:
      the default port for a `URL` parsed by this handler.
    Since:
      1.3

  - ### equals

    protected boolean equals(URL u1, URL u2)
    Provides the default equals calculation. May be overridden by handlers for other protocols that have different requirements for equals(). This method requires that none of its arguments is null. This is guaranteed by the fact that it is only called by java.net.URL class.
    Parameters:
      `u1` - a URL object
      `u2` - a URL object
    Returns:
      `true` if the two urls are considered equal, i.e. they refer to the same fragment in the same file.
    Since:
      1.3

  - ### hashCode

    protected int hashCode(URL u)
    Provides the default hash calculation. May be overridden by handlers for other protocols that have different requirements for hashCode calculation.
    Parameters:
      `u` - a URL object
    Returns:
      an `int` suitable for hash table indexing
    Since:
      1.3

  - ### sameFile

    protected boolean sameFile(URL u1, URL u2)
    Compare two urls to see whether they refer to the same file, i.e., having the same protocol, host, port, and path. This method requires that none of its arguments is null. This is guaranteed by the fact that it is only called indirectly by java.net.URL class.
    Parameters:
      `u1` - a URL object
      `u2` - a URL object
    Returns:
      true if u1 and u2 refer to the same file
    Since:
      1.3

  - ### getHostAddress

    protected InetAddress getHostAddress(URL u)
    Get the IP address of our host. An empty host field or a DNS failure will result in a null return.
    Parameters:
      `u` - a URL object
    Returns:
      an `InetAddress` representing the host IP address.
    Since:
      1.3

  - ### hostsEqual

    protected boolean hostsEqual(URL u1, URL u2)
    Compares the host components of two URLs.
    Parameters:
      `u1` - the URL of the first host to compare
      `u2` - the URL of the second host to compare
    Returns:
      `true` if and only if they are equal, `false` otherwise.
    Since:
      1.3

  - ### toExternalForm

    protected String toExternalForm(URL u)
    Converts a `URL` of a specific protocol to a `String`.
    Parameters:
      `u` - the URL.
    Returns:
      a string representation of the `URL` argument.

  - ### setURL

    protected void setURL(URL u, String protocol, String host, int port, String authority, String userInfo, String path, String query, String ref)
    Sets the fields of the `URL` argument to the indicated values. Only classes derived from URLStreamHandler are able to use this method to set the values of the URL fields.
    Parameters:
      `u` - the URL to modify.
      `protocol` - the protocol name.
      `host` - the remote host value for the URL.
      `port` - the port on the remote machine.
      `authority` - the authority part for the URL.
      `userInfo` - the userInfo part of the URL.
      `path` - the path component of the URL.
      `query` - the query part for the URL.
      `ref` - the reference.
    Throws:
      `SecurityException` - if the protocol handler of the URL is different from this one
      `IllegalArgumentException` - if the implementation of the protocol handler rejects any of the given parameters
      `NullPointerException` - if `u` is `null`
    Since:
      1.3

  - ### setURL

    @Deprecated protected void setURL(URL u, String protocol, String host, int port, String file, String ref)
    Deprecated.
    Use setURL(URL, String, String, int, String, String, String, String);
    Sets the fields of the `URL` argument to the indicated values. Only classes derived from URLStreamHandler are able to use this method to set the values of the URL fields.
    Parameters:
      `u` - the URL to modify.
      `protocol` - the protocol name. This value is ignored since 1.2.
      `host` - the remote host value for the URL.
      `port` - the port on the remote machine.
      `file` - the file.
      `ref` - the reference.
    Throws:
      `SecurityException` - if the protocol handler of the URL is different from this one
      `IllegalArgumentException` - if the implementation of the protocol handler rejects any of the given parameters
      `NullPointerException` - if `u` is `null`