com.firefly.utils.io.Resource Maven / Gradle / Ivy
package com.firefly.utils.io;
import java.io.File;
import java.io.IOException;
import java.net.URI;
import java.net.URL;
/**
* Interface for a resource descriptor that abstracts from the actual type of
* underlying resource, such as a file or class path resource.
*
*
* An InputStream can be opened for every resource if it exists in physical
* form, but a URL or File handle can just be returned for certain resources.
* The actual behavior is implementation-specific.
*
* @see #getInputStream()
* @see #getURL()
* @see #getURI()
* @see #getFile()
* @see WritableResource
* @see ContextResource
* @see FileSystemResource
* @see ClassPathResource
* @see UrlResource
* @see ByteArrayResource
* @see InputStreamResource
* @see PathResource
*/
public interface Resource extends InputStreamSource {
/**
* Return whether this resource actually exists in physical form.
*
* This method performs a definitive existence check, whereas the existence
* of a {@code Resource} handle only guarantees a valid descriptor handle.
*/
boolean exists();
/**
* Return whether the contents of this resource can be read, e.g. via
* {@link #getInputStream()} or {@link #getFile()}.
*
* Will be {@code true} for typical resource descriptors; note that actual
* content reading may still fail when attempted. However, a value of
* {@code false} is a definitive indication that the resource content cannot
* be read.
*
* @see #getInputStream()
*/
boolean isReadable();
/**
* Return whether this resource represents a handle with an open stream. If
* true, the InputStream cannot be read multiple times, and must be read and
* closed to avoid resource leaks.
*
* Will be {@code false} for typical resource descriptors.
*/
boolean isOpen();
/**
* Return a URL handle for this resource.
*
* @throws IOException
* if the resource cannot be resolved as URL, i.e. if the
* resource is not available as descriptor
*/
URL getURL() throws IOException;
/**
* Return a URI handle for this resource.
*
* @throws IOException
* if the resource cannot be resolved as URI, i.e. if the
* resource is not available as descriptor
*/
URI getURI() throws IOException;
/**
* Return a File handle for this resource.
*
* @throws IOException
* if the resource cannot be resolved as absolute file path,
* i.e. if the resource is not available in a file system
*/
File getFile() throws IOException;
/**
* Determine the content length for this resource.
*
* @throws IOException
* if the resource cannot be resolved (in the file system or as
* some other known physical resource type)
*/
long contentLength() throws IOException;
/**
* Determine the last-modified timestamp for this resource.
*
* @throws IOException
* if the resource cannot be resolved (in the file system or as
* some other known physical resource type)
*/
long lastModified() throws IOException;
/**
* Create a resource relative to this resource.
*
* @param relativePath
* the relative path (relative to this resource)
* @return the resource handle for the relative resource
* @throws IOException
* if the relative resource cannot be determined
*/
Resource createRelative(String relativePath) throws IOException;
/**
* Determine a filename for this resource, i.e. typically the last part of
* the path: for example, "myfile.txt".
*
* Returns {@code null} if this type of resource does not have a filename.
*/
String getFilename();
/**
* Return a description for this resource, to be used for error output when
* working with the resource.
*
* Implementations are also encouraged to return this value from their
* {@code toString} method.
*
* @see Object#toString()
*/
String getDescription();
}