AutoCloseable
, Closeable
Provides access to the content of a module.
A module reader is intended for cases where access to the resources in a module is required, regardless of whether the module has been loaded. A framework that scans a collection of packaged modules on the file system, for example, may use a module reader to access a specific resource in each module. A module reader is also intended to be used by ClassLoader
implementations that load classes and resources from modules.
A resource in a module is identified by an abstract name that is a '/
'-separated path string. For example, module java.base
may have a resource "java/lang/Object.class
" that, by convention, is the class file for java.lang.Object
. A module reader may treat directories in the module content as resources (whether it does or not is module reader specific). Where the module content contains a directory that can be located as a resource then its name ends with a slash ('/'). The directory can also be located with a name that drops the trailing slash.
A ModuleReader
is open upon creation and is closed by invoking the close
method. Failure to close a module reader may result in a resource leak. The try-with-resources
statement provides a useful construct to ensure that module readers are closed.
A ModuleReader
implementation may require permissions to access resources in the module. Consequently the find
, open
, read
, and list
methods may throw SecurityException
if access is denied by the security manager.
ModuleReader
should take great care when translating an abstract resource name to the location of a resource in a packaged module or on the file system. Implementations are advised to treat resource names with elements such as '.
, '..
', elements containing file separators, or empty elements as "not found". More generally, if the resource name is not in the stream of elements that the list
method returns then the resource should be treated as "not found" to avoid inconsistencies.
void
Closes the module reader.
Finds a resource, returning a URI to the resource in the module.
Lists the contents of the module, returning a stream of elements that are the names of all resources in the module.
Opens a resource, returning an input stream to read the resource in the module.
Reads a resource, returning a byte buffer with the contents of the resource.
default void
If the module reader can determine that the name locates a directory then the resulting URI will end with a slash ('/').
name
- The name of the resource to open for reading
Optional
if the resource is not found or a URI cannot be constructed to locate the resource
IOException
- If an I/O error occurs or the module reader is closed
SecurityException
- If denied by the security manager
The behavior of the input stream when used after the module reader is closed is implementation specific and therefore not specified.
find
method to get a URI to the resource. If found, then it attempts to construct a URL
and open a connection to the resource.
name
- The name of the resource to open for reading
Optional
if not found
IOException
- If an I/O error occurs or the module reader is closed
SecurityException
- If denied by the security manager
Reads a resource, returning a byte buffer with the contents of the resource. The element at the returned buffer's position is the first byte of the resource, the element at the buffer's limit is the last byte of the resource. Once consumed, the
release
method must be invoked. Failure to invoke the
release
method may result in a resource leak.
release
method is to allow module reader implementations manage buffers in an efficient manner.
open
method and reads all bytes from the input stream into a byte buffer.
name
- The name of the resource to read
Optional
if not found
IOException
- If an I/O error occurs or the module reader is closed
SecurityException
- If denied by the security manager
OutOfMemoryError
- If the resource is larger than Integer.MAX_VALUE
, the maximum capacity of a byte buffer
Releases a byte buffer. This method should be invoked after consuming the contents of the buffer returned by the read
method. The behavior of this method when invoked to release a buffer that has already been released, or the behavior when invoked to release a buffer after a ModuleReader
is closed is implementation specific and therefore not specified.
bb
- The byte buffer to release
Lists the contents of the module, returning a stream of elements that are the names of all resources in the module. Whether the stream of elements includes names corresponding to directories in the module is module reader specific.
In lazy implementations then an IOException
may be thrown when using the stream to list the module contents. If this occurs then the IOException
will be wrapped in an UncheckedIOException
and thrown from the method that caused the access to be attempted. SecurityException
may also be thrown when using the stream to list the module contents and access is denied by the security manager.
The returned stream may contain references to one or more open directories in the module. The directories are closed by closing the stream.
The behavior of the stream when used after the module reader is closed is implementation specific and therefore not specified.
IOException
- If an I/O error occurs or the module reader is closed
SecurityException
- If denied by the security manager
Closes the module reader. Once closed then subsequent calls to locate or read a resource will fail by throwing
IOException
.
A module reader is not required to be asynchronously closeable. If a thread is reading a resource and another thread invokes the close method, then the second thread may block until the read operation is complete.
close
in interface AutoCloseable
close
in interface Closeable
IOException
- if an I/O error occurs
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