# Class JarURLConnection

java.lang.Object
java.net.URLConnection
java.net.JarURLConnection

public abstract class JarURLConnection extends URLConnection
A URL Connection to a Java ARchive (JAR) file or an entry in a JAR file.

The syntax of a JAR URL is:

    jar:<url>!/{entry}

for example:

`jar:http://www.foo.com/bar/baz.jar!/COM/foo/Quux.class`

Jar URLs should be used to refer to a JAR file or entries in a JAR file. The example above is a JAR URL which refers to a JAR entry. If the entry name is omitted, the URL refers to the whole JAR file: `jar:http://www.foo.com/bar/baz.jar!/`

Users should cast the generic URLConnection to a JarURLConnection when they know that the URL they created is a JAR URL, and they need JAR-specific functionality. For example:

    URL url = new URL("jar:file:/home/duke/duke.jar!/");
    JarURLConnection jarConnection = (JarURLConnection)url.openConnection();
    Manifest manifest = jarConnection.getManifest();

JarURLConnection instances can only be used to read from JAR files. It is not possible to get a `OutputStream` to modify or write to the underlying JAR file using this class.

Examples:

A Jar entry
  `jar:http://www.foo.com/bar/baz.jar!/COM/foo/Quux.class`
A Jar file
  `jar:http://www.foo.com/bar/baz.jar!/`
A Jar directory
  `jar:http://www.foo.com/bar/baz.jar!/COM/foo/`

`!/` is referred to as the separator.

When constructing a JAR url via `new URL(context, spec)`, the following rules apply:

- if there is no context URL and the specification passed to the URL constructor doesn't contain a separator, the URL is considered to refer to a JarFile.
- if there is a context URL, the context URL is assumed to refer to a JAR file or a Jar directory.
- if the specification begins with a '/', the Jar directory is ignored, and the spec is considered to be at the root of the Jar file.

  Examples:

  context: jar:http://www.foo.com/bar/jar.jar!/, spec:baz/entry.txt
    url:jar:http://www.foo.com/bar/jar.jar!/baz/entry.txt
  context: jar:http://www.foo.com/bar/jar.jar!/baz, spec:entry.txt
    url:jar:http://www.foo.com/bar/jar.jar!/baz/entry.txt
  context: jar:http://www.foo.com/bar/jar.jar!/baz, spec:/entry.txt
    url:jar:http://www.foo.com/bar/jar.jar!/entry.txt

Since:
  1.2
See Also:
  - `URL`
  - `URLConnection`
  - `JarFile`
  - `JarInputStream`
  - `Manifest`
  - `ZipEntry`

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected URLConnection`
  `jarFileURLConnection`
  The connection to the JAR file URL, if the connection has been initiated.

  ### Fields declared in class URLConnection

  `allowUserInteraction, connected, doInput, doOutput, ifModifiedSince, url, useCaches`

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `JarURLConnection(URL url)`
  Creates the new JarURLConnection to the specified URL.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `Attributes`
  `getAttributes()`
  Return the Attributes object for this connection if the URL for it points to a JAR file entry, null otherwise.
  `Certificate[]`
  `getCertificates()`
  Returns the Certificate objects for this connection if the URL for it points to a JAR file entry, null otherwise.
  `String`
  `getEntryName()`
  Return the entry name for this connection.
  `JarEntry`
  `getJarEntry()`
  Return the JAR entry object for this connection, if any.
  `abstract JarFile`
  `getJarFile()`
  Return the JAR file for this connection.
  `URL`
  `getJarFileURL()`
  Returns the URL for the Jar file for this connection.
  `Attributes`
  `getMainAttributes()`
  Returns the main Attributes for the JAR file for this connection.
  `Manifest`
  `getManifest()`
  Returns the Manifest for this connection, or null if none.

  ### Methods declared in class URLConnection

  `addRequestProperty, connect, getAllowUserInteraction, getConnectTimeout, getContent, getContent, getContentEncoding, getContentLength, getContentLengthLong, getContentType, getDate, getDefaultAllowUserInteraction, getDefaultRequestProperty, getDefaultUseCaches, getDefaultUseCaches, getDoInput, getDoOutput, getExpiration, getFileNameMap, getHeaderField, getHeaderField, getHeaderFieldDate, getHeaderFieldInt, getHeaderFieldKey, getHeaderFieldLong, getHeaderFields, getIfModifiedSince, getInputStream, getLastModified, getOutputStream, getPermission, getReadTimeout, getRequestProperties, getRequestProperty, getURL, getUseCaches, guessContentTypeFromName, guessContentTypeFromStream, setAllowUserInteraction, setConnectTimeout, setContentHandlerFactory, setDefaultAllowUserInteraction, setDefaultRequestProperty, setDefaultUseCaches, setDefaultUseCaches, setDoInput, setDoOutput, setFileNameMap, setIfModifiedSince, setReadTimeout, setRequestProperty, setUseCaches, toString`

  ### Methods declared in class Object

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

- ## Field Details

  - ### jarFileURLConnection

    protected URLConnection jarFileURLConnection
    The connection to the JAR file URL, if the connection has been initiated. This should be set by connect.

- ## Constructor Details

  - ### JarURLConnection

    protected JarURLConnection(URL url) throws MalformedURLException
    Creates the new JarURLConnection to the specified URL.
    Parameters:
      `url` - the URL
    Throws:
      `MalformedURLException` - if no legal protocol could be found in a specification string or the string could not be parsed.

- ## Method Details

  - ### getJarFileURL

    public URL getJarFileURL()
    Returns the URL for the Jar file for this connection.
    Returns:
      the URL for the Jar file for this connection.

  - ### getEntryName

    public String getEntryName()
    Return the entry name for this connection. This method returns null if the JAR file URL corresponding to this connection points to a JAR file and not a JAR file entry.
    Returns:
      the entry name for this connection, if any.

  - ### getJarFile

    public abstract JarFile getJarFile() throws IOException
    Return the JAR file for this connection.
    Returns:
      the JAR file for this connection. If the connection is a connection to an entry of a JAR file, the JAR file object is returned
    Throws:
      `IOException` - if an IOException occurs while trying to connect to the JAR file for this connection.
    See Also:
      - `URLConnection.connect()`

  - ### getManifest

    public Manifest getManifest() throws IOException
    Returns the Manifest for this connection, or null if none.
    Returns:
      the manifest object corresponding to the JAR file object for this connection.
    Throws:
      `IOException` - if getting the JAR file for this connection causes an IOException to be thrown.
    See Also:
      - `getJarFile()`

  - ### getJarEntry

    public JarEntry getJarEntry() throws IOException
    Return the JAR entry object for this connection, if any. This method returns null if the JAR file URL corresponding to this connection points to a JAR file and not a JAR file entry.
    Returns:
      the JAR entry object for this connection, or null if the JAR URL for this connection points to a JAR file.
    Throws:
      `IOException` - if getting the JAR file for this connection causes an IOException to be thrown.
    See Also:
      - `getJarFile()`
      - `getJarEntry()`

  - ### getAttributes

    public Attributes getAttributes() throws IOException
    Return the Attributes object for this connection if the URL for it points to a JAR file entry, null otherwise.
    Returns:
      the Attributes object for this connection if the URL for it points to a JAR file entry, null otherwise.
    Throws:
      `IOException` - if getting the JAR entry causes an IOException to be thrown.
    See Also:
      - `getJarEntry()`

  - ### getMainAttributes

    public Attributes getMainAttributes() throws IOException
    Returns the main Attributes for the JAR file for this connection.
    Returns:
      the main Attributes for the JAR file for this connection.
    Throws:
      `IOException` - if getting the manifest causes an IOException to be thrown.
    See Also:
      - `getJarFile()`
      - `getManifest()`

  - ### getCertificates

    public Certificate[] getCertificates() throws IOException
    Returns the Certificate objects for this connection if the URL for it points to a JAR file entry, null otherwise. This method can only be called once the connection has been completely verified by reading from the input stream until the end of the stream has been reached. Otherwise, this method will return `null`.

    The returned certificate array comprises all the signer certificates that were used to verify this entry. Each signer certificate is followed by its supporting certificate chain (which may be empty). Each signer certificate and its supporting certificate chain are ordered bottom-to-top (i.e., with the signer certificate first and the (root) certificate authority last).

    API Note:
      The verification process does not include validating or establishing trust in the code signers. A caller should perform additional checks, such as using a `CertPathValidator` to validate each signer's certificate chain, and determining whether to trust the entry signed by the signers.
    Returns:
      the Certificate objects for this connection if the URL for it points to a JAR file entry, null otherwise.
    Throws:
      `IOException` - if getting the JAR entry causes an IOException to be thrown.
    See Also:
      - `getJarEntry()`