https://openjdk.java.net/ 
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * accompanied this code).
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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 
considered for processing by the tool in a subsequent round of processing after the close method has been called on the Writer or 
OutputStream used to write the contents of the file. Three kinds of files are distinguished: source files, class files, and auxiliary resource files. 
 There are two distinguished supported locations (subtrees within the logical file system) where newly created files are placed: one for new source files, and one for new
class files. (These might be specified on a tool's command line, for example, using flags such as -s and -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 '/'; '.' and '..' are invalid path segments. A valid relative name must match the "path-rootless" rule of RFC 3986, section
3.3.

The file creation methods take a variable number of arguments to
allow the originating elements to be provided as hints to the tool infrastructure to better manage dependencies. The originating elements are the types or packages (representing 
package-info files) or modules (representing 
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, 
GeneratedFromUserSource, in response to processing 
 @Generate
 public class UserSource {}

 the type element for UserSource should be passed as part of the creation method call as in: 
     filer.createSourceFile("GeneratedFromUserSource",
                            eltUtils.getTypeElement("UserSource"));


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.

 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 FilerException, as will attempting to create both a class file and source file for the same type name or same package name. The 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 FilerException. 
 In general, processors must not knowingly attempt to overwrite existing files that were not generated by some processor. A 
Filer may reject attempts to open a file corresponding to an existing type, like 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. 
 Processors can indicate a source or class file is generated by including a javax.annotation.Generated annotation if the environment is configured so that that type is accessible. 
Author:Joseph D. Darcy, Scott Seligman, Peter von der Ahé
API Note:Some of the effect of overwriting a file can be
achieved by using a 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.
Since:1.6
/**
 * 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&nbsp;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.
 *
 * @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 Ah&eacute;
 * @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 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). 
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 name argument be the package's name followed by ".package-info"; to create a source file for an unnamed package, use "package-info". 
The optional module name is prefixed to the type name or package name and separated using a "/" character. For example, to create a source file for type a.B in module foo, use a name argument of "foo/a.B". 
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 FilerException is thrown. An implementation may use information about the configuration of the annotation processing tool as part of the inference. 
Creating a source file in or for an unnamed package in a named
module is not supported.

Params:
  • name –  canonical (fully qualified) name of the principal type being declared in this file or a package name followed by ".package-info" for a package information file
  • originatingElements – type or package or module elements causally associated with the creation of this file, may be elided or null
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.
  • IOException – if the file cannot be created
API Note:To use a particular charset to encode the contents of the file, an OutputStreamWriter with the chosen charset can be created from the OutputStream from the returned object. If the Writer from the returned object is directly used for writing, its charset is determined by the implementation. An annotation processing tool may have an -encoding flag or analogous option for specifying this; otherwise, it will typically be the platform's default encoding. 
To avoid subsequent errors, the contents of the source file should be compatible with the source version being used for this run.
Implementation Note:In the reference implementation, if the annotation
processing tool is processing a single module M,
then M is used as the module for files created without an explicit module prefix. If the tool is processing multiple modules, and 
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.
Returns:a JavaFileObject to write the new source file
@jls7.3 Compilation Units
/**
     * 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 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). 
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 name argument be the package's name followed by ".package-info"; creating a class file for an unnamed package is not supported. 
The optional module name is prefixed to the type name or package name and separated using a "/" character. For example, to create a class file for type a.B in module foo, use a name argument of "foo/a.B". 
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 FilerException is thrown. An implementation may use information about the configuration of the annotation processing tool as part of the inference. 
Creating a class file in or for an unnamed package in a named
module is not supported.

Params:
  • name – binary name of the type being written or a package name followed by ".package-info" for a package information file
  • originatingElements – type or package or module elements causally associated with the creation of this file, may be elided or null
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.
  • IOException – if the file cannot be created
API Note:To avoid subsequent errors, the contents of the class file should be compatible with the source version being used for this run.
Implementation Note:In the reference implementation, if the annotation
processing tool is processing a single module M,
then M is used as the module for files created without an explicit module prefix. If the tool is processing multiple modules, and 
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.
Returns:a JavaFileObject to write the new class file
/**
     * 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 CLASS_OUTPUT and 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 location, moduleAndPkg, and relativeName. If moduleAndPkg contains a "/" character, the prefix before the "/" character is the module name and the suffix after the "/" character is the package name. The package suffix may be empty. If moduleAndPkg does not contain a "/" character, the entire argument is interpreted as a package name. 
If the given location is neither a 
module oriented location, nor an 
output location containing multiple modules, and the explicit module prefix is given, FilerException is thrown. 
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 FilerException is thrown. An implementation may use information about the configuration of the annotation processing tool as part of the inference. 
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.

Params:
  • location – location of the new file
  • moduleAndPkg – module and/or package relative to which the file
          should be named, or the empty string if none
  • relativeName – final pathname components of the file
  • originatingElements – type or package or module elements causally associated with the creation of this file, may be elided or null
Throws:
Implementation Note:In the reference implementation, if the annotation
processing tool is processing a single module M,
then M is used as the module for files created without an explicit module prefix. If the tool is processing multiple modules, and 
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.
Returns:a FileObject to write the new resource
/**
     * 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 CLASS_OUTPUT and SOURCE_OUTPUT must be supported. 
If moduleAndPkg contains a "/" character, the prefix before the "/" character is the module name and the suffix after the "/" character is the package name. The package suffix may be empty; however, if a module name is present, it must be nonempty. If moduleAndPkg does not contain a "/" character, the entire argument is interpreted as a package name. 
If the given location is neither a 
module oriented location, nor an 
output location containing multiple modules, and the explicit module prefix is given, FilerException is thrown. 
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 FilerException is thrown. An implementation may use information about the configuration of the annotation processing tool as part of the inference. 
Params:
  • location – location of the file
  • moduleAndPkg – module and/or package relative to which the file
         should be searched for, or the empty string if none
  • relativeName – final pathname components of the file
Throws:
Implementation Note:In the reference implementation, if the annotation
processing tool is processing a single module M,
then M is used as the module for files read without an explicit module prefix. If the tool is processing multiple modules, and 
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.
Returns:an object to read the file
/**
     * 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;
}