Java tutorial
/* * Copyright (c) 2005, 2019, Oracle and/or its affiliates. All rights reserved. * 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. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.annotation.processing; import javax.tools.JavaFileManager; import javax.tools.*; import javax.lang.model.element.Element; import javax.lang.model.util.Elements; 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</em> 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) or modules (representing {@code * module-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><pre> * @Generate * public class UserSource {} * </pre></blockquote> * * the type element for {@code UserSource} should be passed as part of * the creation method call as in: * * <blockquote><pre> * filer.createSourceFile("GeneratedFromUserSource", * eltUtils.getTypeElement("UserSource")); * </pre></blockquote> * * 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 a {@code javax.annotation.Generated} annotation if the * environment is configured so that that type is accessible. * * @apiNote Some of the effect of overwriting a file can be * achieved by using a <i>decorator</i>-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. A source file for a type, or a package can * be created. * * The file's name and path (relative to the {@linkplain * StandardLocation#SOURCE_OUTPUT root output location for source * files}) are based on the name of the item to be declared in * that file as well as the specified module for the item (if * any). * * If more than one type is being declared in a single file (that * is, a single compilation unit), the name of the file should * correspond to the name of the principal top-level type (the * public one, for example). * * <p>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 the {@code name} argument be the * package's name followed by {@code ".package-info"}; to create a * source file for an unnamed package, use {@code "package-info"}. * * <p>The optional module name is prefixed to the type name or * package name and separated using a "{@code /}" character. For * example, to create a source file for type {@code a.B} in module * {@code foo}, use a {@code name} argument of {@code "foo/a.B"}. * * <p>If no explicit module prefix is given and modules are supported * in the environment, a suitable module is inferred. If a suitable * module cannot be inferred {@link FilerException} is thrown. * An implementation may use information about the configuration of * the annotation processing tool as part of the inference. * * <p>Creating a source file in or for an unnamed package in a named * module is <em>not</em> supported. * * @apiNote 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. * * @implNote In the reference implementation, if the annotation * processing tool is processing a single module <i>M</i>, * then <i>M</i> is used as the module for files created without * an explicit module prefix. If the tool is processing multiple * modules, and {@link * Elements#getPackageElement(java.lang.CharSequence) * Elements.getPackageElement(package-of(name))} * returns a package, the module that owns the returned package is used * as the target module. A separate option may be used to provide the target * module if it cannot be determined using the above rules. * * @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 or module 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, the name is * otherwise not valid for the entity requested to being created, * if the target module cannot be determined, if the target * module is not writable, or a module is specified when the environment * doesn't support modules. * @throws IOException if the file cannot be created * @jls 7.3 Compilation Units */ JavaFileObject createSourceFile(CharSequence name, Element... originatingElements) throws IOException; /** * Creates a new class file, and returns an object to allow * writing to it. A class file for a type, or a package can * be created. * * 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 item to be declared as * well as the specified module for the item (if any). * * <p>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 the {@code name} argument be the * package's name followed by {@code ".package-info"}; creating a * class file for an unnamed package is not supported. * * <p>The optional module name is prefixed to the type name or * package name and separated using a "{@code /}" character. For * example, to create a class file for type {@code a.B} in module * {@code foo}, use a {@code name} argument of {@code "foo/a.B"}. * * <p>If no explicit module prefix is given and modules are supported * in the environment, a suitable module is inferred. If a suitable * module cannot be inferred {@link FilerException} is thrown. * An implementation may use information about the configuration of * the annotation processing tool as part of the inference. * * <p>Creating a class file in or for an unnamed package in a named * module is <em>not</em> supported. * * @apiNote 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. * * @implNote In the reference implementation, if the annotation * processing tool is processing a single module <i>M</i>, * then <i>M</i> is used as the module for files created without * an explicit module prefix. If the tool is processing multiple * modules, and {@link * Elements#getPackageElement(java.lang.CharSequence) * Elements.getPackageElement(package-of(name))} * returns a package, the module that owns the returned package is used * as the target module. A separate option may be used to provide the target * module if it cannot be determined using the above rules. * * @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 or module 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, the name is * not valid for a type, if the target module cannot be determined, * if the target module is not writable, or a module is specified when * the environment doesn't support modules. * @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 module * and/or 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 moduleAndPkg}, and {@code relativeName}. * * If {@code moduleAndPkg} contains a "{@code /}" character, the * prefix before the "{@code /}" character is the module name and * the suffix after the "{@code /}" character is the package * name. The package suffix may be empty. If {@code moduleAndPkg} * does not contain a "{@code /}" character, the entire argument * is interpreted as a package name. * * <p>If the given location is neither a {@linkplain * JavaFileManager.Location#isModuleOrientedLocation() * module oriented location}, nor an {@linkplain * JavaFileManager.Location#isOutputLocation() * output location containing multiple modules}, and the explicit * module prefix is given, {@link FilerException} is thrown. * * <p>If the given location is either a module oriented location, * or an output location containing multiple modules, and no explicit * modules prefix is given, a suitable module is * inferred. If a suitable module cannot be inferred {@link * FilerException} is thrown. An implementation may use information * about the configuration of the annotation processing tool * as part of the inference. * * <p>Files created via this method are <em>not</em> 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. * * @implNote In the reference implementation, if the annotation * processing tool is processing a single module <i>M</i>, * then <i>M</i> is used as the module for files created without * an explicit module prefix. If the tool is processing multiple * modules, and {@link * Elements#getPackageElement(java.lang.CharSequence) * Elements.getPackageElement(package-of(name))} * returns a package, the module that owns the returned package is used * as the target module. A separate option may be used to provide the target * module if it cannot be determined using the above rules. * * @param location location of the new file * @param moduleAndPkg module and/or 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 or module 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, if the target module cannot be determined, * or if the target module is not writable, or if an explicit * target module is specified and the location does not support it. * @throws IllegalArgumentException for an unsupported location * @throws IllegalArgumentException if {@code moduleAndPkg} is ill-formed * @throws IllegalArgumentException if {@code relativeName} is not relative */ FileObject createResource(JavaFileManager.Location location, CharSequence moduleAndPkg, 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. * * <p>If {@code moduleAndPkg} contains a "{@code /}" character, the * prefix before the "{@code /}" character is the module name and * the suffix after the "{@code /}" character is the package * name. The package suffix may be empty; however, if a module * name is present, it must be nonempty. If {@code moduleAndPkg} * does not contain a "{@code /}" character, the entire argument * is interpreted as a package name. * * <p>If the given location is neither a {@linkplain * JavaFileManager.Location#isModuleOrientedLocation() * module oriented location}, nor an {@linkplain * JavaFileManager.Location#isOutputLocation() * output location containing multiple modules}, and the explicit * module prefix is given, {@link FilerException} is thrown. * * <p>If the given location is either a module oriented location, * or an output location containing multiple modules, and no explicit * modules prefix is given, a suitable module is * inferred. If a suitable module cannot be inferred {@link * FilerException} is thrown. An implementation may use information * about the configuration of the annotation processing tool * as part of the inference. * * @implNote In the reference implementation, if the annotation * processing tool is processing a single module <i>M</i>, * then <i>M</i> is used as the module for files read without * an explicit module prefix. If the tool is processing multiple * modules, and {@link * Elements#getPackageElement(java.lang.CharSequence) * Elements.getPackageElement(package-of(name))} * returns a package, the module that owns the returned package is used * as the source module. A separate option may be used to provide the target * module if it cannot be determined using the above rules. * * @param location location of the file * @param moduleAndPkg module and/or package relative to which the file * should be searched for, 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, if the source module cannot be determined, * or if the target module is not writable, or if an explicit target * module is specified and the location does not support it. * @throws IOException if the file cannot be opened * @throws IllegalArgumentException for an unsupported location * @throws IllegalArgumentException if {@code moduleAndPkg} is ill-formed * @throws IllegalArgumentException if {@code relativeName} is not relative */ FileObject getResource(JavaFileManager.Location location, CharSequence moduleAndPkg, CharSequence relativeName) throws IOException; }