Filer.java

/*
 * Copyright (c) 2005, 2017, 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
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package javax.annotation.processing;

import java.io.IOException;

import javax.lang.model.element.Element;
import javax.lang.model.util.Elements;
import javax.tools.FileObject;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.StandardLocation;

/**
 * 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
 * &quot;path-rootless&quot; 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>
 *  &#64;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.
 *
 * @author Joseph D. Darcy
 * @author Scott Seligman
 * @author Peter von der Ah&eacute;
 * @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.
 * @since 1.6
 */
// 用于在注解处理器工作期间创建/读取文件
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.
     *
     * @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
     * @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.
     * @jls 7.3 Compilation Units
     */
    /*
     * 用来创建一个.java文件，name是全限定名，最后一个参数目前没用
     * 文件存放路径是相对StandardLocation#SOURCE_OUTPUT而言的
     */
    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.
     *
     * @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
     * @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.
     */
    /*
     * 用来创建一个.class文件，name是全限定名，最后一个参数目前没用
     * 文件存放路径是相对StandardLocation#CLASS_OUTPUT而言的
     */
    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.
     *
     * @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
     * @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.
     */
    /*
     * 用来创建一个资源文件，可以是任意类型。moduleAndPkg是包名，relativeName是资源名称（带后缀），最后一个参数目前没用
     * 文件存放路径由location指定
     */
    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.
     *
     * @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
     * @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.
     */
    /*
     * 用来读取一个资源文件，可以是任意类型。moduleAndPkg是包名，relativeName是资源名称（带后缀）
     * 文件读取路径由location指定
     */
    FileObject getResource(JavaFileManager.Location location, CharSequence moduleAndPkg, CharSequence relativeName)
        throws IOException;
}