The Filer.java Java example source code
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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package javax.annotation.processing;
import javax.tools.JavaFileManager;
import javax.tools.*;
import javax.lang.model.element.Element;
import java.io.IOException;
/**
* This interface supports the creation of new files by an annotation
* processor. Files created in this way will be known to the
* annotation processing tool implementing this interface, better
* enabling the tool to manage them. Source and class files so
* created will be {@linkplain RoundEnvironment#getRootElements
* considered for processing} by the tool in a subsequent {@linkplain
* RoundEnvironment round of processing} after the {@code close}
* method has been called on the {@code Writer} or {@code
* OutputStream} used to write the contents of the file.
*
* Three kinds of files are distinguished: source files, class files,
* and auxiliary resource files.
*
* <p> There are two distinguished supported locations (subtrees
* within the logical file system) where newly created files are
* placed: one for {@linkplain
* javax.tools.StandardLocation#SOURCE_OUTPUT new source files}, and
* one for {@linkplain javax.tools.StandardLocation#CLASS_OUTPUT new
* class files}. (These might be specified on a tool's command line,
* for example, using flags such as {@code -s} and {@code -d}.) The
* actual locations for new source files and new class files may or
* may not be distinct on a particular run of the tool. Resource
* files may be created in either location. The methods for reading
* and writing resources take a relative name argument. A relative
* name is a non-null, non-empty sequence of path segments separated
* by {@code '/'}; {@code '.'} and {@code '..'} are invalid path
* segments. A valid relative name must match the
* "path-rootless" rule of <a
* href="http://www.ietf.org/rfc/rfc3986.txt">RFC 3986</a>, section
* 3.3.
*
* <p>The file creation methods take a variable number of arguments to
* allow the <em>originating elements to be provided as hints to
* the tool infrastructure to better manage dependencies. The
* originating elements are the types or packages (representing {@code
* package-info} files) which caused an annotation processor to
* attempt to create a new file. For example, if an annotation
* processor tries to create a source file, {@code
* GeneratedFromUserSource}, in response to processing
*
* <blockquote>
* @Generate
* public class UserSource {}
* </pre>
*
* the type element for {@code UserSource} should be passed as part of
* the creation method call as in:
*
* <blockquote>
* filer.createSourceFile("GeneratedFromUserSource",
* eltUtils.getTypeElement("UserSource"));
* </pre>
*
* If there are no originating elements, none need to be passed. This
* information may be used in an incremental environment to determine
* the need to rerun processors or remove generated files.
* Non-incremental environments may ignore the originating element
* information.
*
* <p> During each run of an annotation processing tool, a file with a
* given pathname may be created only once. If that file already
* exists before the first attempt to create it, the old contents will
* be deleted. Any subsequent attempt to create the same file during
* a run will throw a {@link FilerException}, as will attempting to
* create both a class file and source file for the same type name or
* same package name. The {@linkplain Processor initial inputs} to
* the tool are considered to be created by the zeroth round;
* therefore, attempting to create a source or class file
* corresponding to one of those inputs will result in a {@link
* FilerException}.
*
* <p> In general, processors must not knowingly attempt to overwrite
* existing files that were not generated by some processor. A {@code
* Filer} may reject attempts to open a file corresponding to an
* existing type, like {@code java.lang.Object}. Likewise, the
* invoker of the annotation processing tool must not knowingly
* configure the tool such that the discovered processors will attempt
* to overwrite existing files that were not generated.
*
* <p> Processors can indicate a source or class file is generated by
* including an {@link javax.annotation.Generated @Generated}
* annotation.
*
* <p> Note that some of the effect of overwriting a file can be
* achieved by using a <i>decorator-style pattern. Instead of
* modifying a class directly, the class is designed so that either
* its superclass is generated by annotation processing or subclasses
* of the class are generated by annotation processing. If the
* subclasses are generated, the parent class may be designed to use
* factories instead of public constructors so that only subclass
* instances would be presented to clients of the parent class.
*
* @author Joseph D. Darcy
* @author Scott Seligman
* @author Peter von der Ahé
* @since 1.6
*/
public interface Filer {
/**
* Creates a new source file and returns an object to allow
* writing to it. The file's name and path (relative to the
* {@linkplain StandardLocation#SOURCE_OUTPUT root output location
* for source files}) are based on the type to be declared in that
* file. If more than one type is being declared, the name of the
* principal top-level type (the public one, for example) should
* be used. A source file can also be created to hold information
* about a package, including package annotations. To create a
* source file for a named package, have {@code name} be the
* package's name followed by {@code ".package-info"}; to create a
* source file for an unnamed package, use {@code "package-info"}.
*
* <p> Note that to use a particular {@linkplain
* java.nio.charset.Charset charset} to encode the contents of the
* file, an {@code OutputStreamWriter} with the chosen charset can
* be created from the {@code OutputStream} from the returned
* object. If the {@code Writer} from the returned object is
* directly used for writing, its charset is determined by the
* implementation. An annotation processing tool may have an
* {@code -encoding} flag or analogous option for specifying this;
* otherwise, it will typically be the platform's default
* encoding.
*
* <p>To avoid subsequent errors, the contents of the source file
* should be compatible with the {@linkplain
* ProcessingEnvironment#getSourceVersion source version} being used
* for this run.
*
* @param name canonical (fully qualified) name of the principal type
* being declared in this file or a package name followed by
* {@code ".package-info"} for a package information file
* @param originatingElements type or package elements causally
* associated with the creation of this file, may be elided or
* {@code null}
* @return a {@code JavaFileObject} to write the new source file
* @throws FilerException if the same pathname has already been
* created, the same type has already been created, or the name is
* not valid for a type
* @throws IOException if the file cannot be created
*/
JavaFileObject createSourceFile(CharSequence name,
Element... originatingElements) throws IOException;
/**
* Creates a new class file, and returns an object to allow
* writing to it. The file's name and path (relative to the
* {@linkplain StandardLocation#CLASS_OUTPUT root output location
* for class files}) are based on the name of the type being
* written. A class file can also be created to hold information
* about a package, including package annotations. To create a
* class file for a named package, have {@code name} be the
* package's name followed by {@code ".package-info"}; creating a
* class file for an unnamed package is not supported.
*
* <p>To avoid subsequent errors, the contents of the class file
* should be compatible with the {@linkplain
* ProcessingEnvironment#getSourceVersion source version} being used
* for this run.
*
* @param name binary name of the type being written or a package name followed by
* {@code ".package-info"} for a package information file
* @param originatingElements type or package elements causally
* associated with the creation of this file, may be elided or
* {@code null}
* @return a {@code JavaFileObject} to write the new class file
* @throws FilerException if the same pathname has already been
* created, the same type has already been created, or the name is
* not valid for a type
* @throws IOException if the file cannot be created
*/
JavaFileObject createClassFile(CharSequence name,
Element... originatingElements) throws IOException;
/**
* Creates a new auxiliary resource file for writing and returns a
* file object for it. The file may be located along with the
* newly created source files, newly created binary files, or
* other supported location. The locations {@link
* StandardLocation#CLASS_OUTPUT CLASS_OUTPUT} and {@link
* StandardLocation#SOURCE_OUTPUT SOURCE_OUTPUT} must be
* supported. The resource may be named relative to some package
* (as are source and class files), and from there by a relative
* pathname. In a loose sense, the full pathname of the new file
* will be the concatenation of {@code location}, {@code pkg}, and
* {@code relativeName}.
*
* <p>Files created via this method are not registered for
* annotation processing, even if the full pathname of the file
* would correspond to the full pathname of a new source file
* or new class file.
*
* @param location location of the new file
* @param pkg package relative to which the file should be named,
* or the empty string if none
* @param relativeName final pathname components of the file
* @param originatingElements type or package elements causally
* associated with the creation of this file, may be elided or
* {@code null}
* @return a {@code FileObject} to write the new resource
* @throws IOException if the file cannot be created
* @throws FilerException if the same pathname has already been
* created
* @throws IllegalArgumentException for an unsupported location
* @throws IllegalArgumentException if {@code relativeName} is not relative
*/
FileObject createResource(JavaFileManager.Location location,
CharSequence pkg,
CharSequence relativeName,
Element... originatingElements) throws IOException;
/**
* Returns an object for reading an existing resource. The
* locations {@link StandardLocation#CLASS_OUTPUT CLASS_OUTPUT}
* and {@link StandardLocation#SOURCE_OUTPUT SOURCE_OUTPUT} must
* be supported.
*
* @param location location of the file
* @param pkg package relative to which the file should be searched,
* or the empty string if none
* @param relativeName final pathname components of the file
* @return an object to read the file
* @throws FilerException if the same pathname has already been
* opened for writing
* @throws IOException if the file cannot be opened
* @throws IllegalArgumentException for an unsupported location
* @throws IllegalArgumentException if {@code relativeName} is not relative
*/
FileObject getResource(JavaFileManager.Location location,
CharSequence pkg,
CharSequence relativeName) throws IOException;
}
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