- All Superinterfaces:
AutoCloseable,Closeable
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 byClassLoader 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, modulejava.base may have a resource "java/lang/Object.class" that, by convention, is the class file forjava.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.
AModuleReader isopen upon creation and is closed by invoking theclose 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.
AModuleReader implementation may require permissions to access resources in the module. Consequently thefind,open,read, andlist methods may throw SecurityException if access is denied by the security manager.
- Implementation Requirements:
- Implementations of
ModuleReadershould 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 thelistmethod returns then the resource should be treated as "not found" to avoid inconsistencies. - Since:
- 9
- See Also:
Method Summary
Modifier and TypeMethodDescriptionvoidclose()Closes the module reader.Finds a resource, returning a URI to the resource in the module.list()Lists the contents of the module, returning a stream of elements that are the names of all resources in the module.defaultOptional<InputStream> Opens a resource, returning an input stream to read the resource in the module.defaultOptional<ByteBuffer> Reads a resource, returning a byte buffer with the contents of the resource.default voidrelease(ByteBuffer bb) Releases a byte buffer.
Method Details
find
Finds a resource, returning a URI to the resource in the module.If the module reader can determine that the name locates a directory then the resulting URI will end with a slash ('/').
- Parameters:
name- The name of the resource to open for reading- Returns:
- A URI to the resource; an empty
Optionalif the resource is not found or a URI cannot be constructed to locate the resource - Throws:
IOException- If an I/O error occurs or the module reader is closedSecurityException- If denied by the security manager- See Also:
open
Opens a resource, returning an input stream to read the resource in the module.The behavior of the input stream when used after the module reader is closed is implementation specific and therefore not specified.
- Implementation Requirements:
- The default implementation invokes the
findmethod to get a URI to the resource. If found, then it attempts to construct aURLand open a connection to the resource. - Parameters:
name- The name of the resource to open for reading- Returns:
- An input stream to read the resource or an empty
Optionalif not found - Throws:
IOException- If an I/O error occurs or the module reader is closedSecurityException- If denied by the security manager
read
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, thereleasemethod must be invoked. Failure to invoke thereleasemethod may result in a resource leak.- API Note:
- This method is intended for high-performance class loading. It is not capable (or intended) to read arbitrary large resources that could potentially be 2GB or larger. The rationale for using this method in conjunction with the
releasemethod is to allow module reader implementations manage buffers in an efficient manner. - Implementation Requirements:
- The default implementation invokes the
openmethod and reads all bytes from the input stream into a byte buffer. - Parameters:
name- The name of the resource to read- Returns:
- A byte buffer containing the contents of the resource or an empty
Optionalif not found - Throws:
IOException- If an I/O error occurs or the module reader is closedSecurityException- If denied by the security managerOutOfMemoryError- If the resource is larger thanInteger.MAX_VALUE, the maximum capacity of a byte buffer- See Also:
release
Releases a byte buffer. This method should be invoked after consuming the contents of the buffer returned by thereadmethod. 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 aModuleReaderis closed is implementation specific and therefore not specified.- Implementation Requirements:
- The default implementation doesn't do anything except check if the byte buffer is null.
- Parameters:
bb- The byte buffer to release
list
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
IOExceptionmay be thrown when using the stream to list the module contents. If this occurs then theIOExceptionwill be wrapped in anUncheckedIOExceptionand thrown from the method that caused the access to be attempted.SecurityExceptionmay 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.
- API Note:
- This method should be used within a try-with-resources statement or similar control structure to ensure that any open directories referenced by the stream are closed promptly after the stream's operations have completed.
- Returns:
- A stream of elements that are the names of all resources in the module
- Throws:
IOException- If an I/O error occurs or the module reader is closedSecurityException- If denied by the security manager
close
Closes the module reader. Once closed then subsequent calls to locate or read a resource will fail by throwingIOException.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.
- Specified by:
closein interfaceAutoCloseable- Specified by:
closein interfaceCloseable- Throws:
IOException- if an I/O error occurs