Filer


1   /*
2    * @(#)Filer.java   1.10 06/08/28
3    *
4    * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL.  Use is subject to license terms.
6    */
7   
8   package javax.annotation.processing;
9   
10  import javax.tools.JavaFileManager;
11  import javax.tools.*;
12  import javax.lang.model.element.Element;
13  import java.io.IOException  ;
14  
15  /**
16   * This interface supports the creation of new files by an annotation
17   * processor.  Files created in this way will be known to the
18   * annotation processing tool implementing this interface, better
19   * enabling the tool to manage them.  Source and class files so
20   * created will be considered for processing by the tool after the
21   * {@code close} method has been called on the {@code Writer} or
22   * {@code OutputStream} used to write the contents of the file.
23   *
24   * Three kinds of files are distinguished: source files, class files,
25   * and auxiliary resource files.
26   *
27   * <p> There are two distinguished supported locations (subtrees
28   * within the logical file system) where newly created files are
29   * placed: one for {@linkplain
30   * javax.tools.StandardLocation#SOURCE_OUTPUT new source files}, and
31   * one for {@linkplain javax.tools.StandardLocation#CLASS_OUTPUT new
32   * class files}.  (These might be specified on a tool's command line,
33   * for example, using flags such as {@code -s} and {@code -d}.)  The
34   * actual locations for new source files and new class files may or
35   * may not be distinct on a particular run of the tool.  Resource
36   * files may be created in either location.  The methods for reading
37   * and writing resources take a relative name argument.  A relative
38   * name is a non-null, non-empty sequence of path segments separated
39   * by {@code '/'}; {@code '.'} and {@code '..'} are invalid path
40   * segments.  A valid relative name must match the
41   * &quot;path-rootless&quot; rule of <a
42   * HREF="http://www.ietf.org/rfc/rfc3986.txt">RFC 3986</a>, section
43   * 3.3.
44   *
45   * <p>The file creation methods take a variable number of arguments to
46   * allow the <em>originating elements</em> to be provided as hints to
47   * the tool infrastructure to better manage dependencies.  The
48   * originating elements are the types or packages (representing {@code
49   * package-info} files) which caused an annotation processor to
50   * attempt to create a new file.  For example, if an annotation
51   * processor tries to create a source file, {@code
52   * GeneratedFromUserSource}, in response to processing
53   *
54   * <blockquote><pre>
55   *  &#64;Generate
56   *  public class UserSource {}
57   * </pre></blockquote>
58   * 
59   * the type element for {@code UserSource} should be passed as part of
60   * the creation method call as in:
61   *
62   * <blockquote><pre>
63   *      filer.createSourceFile("GeneratedFromUserSource",
64   *                             eltUtils.getTypeElement("UserSource"));
65   * </pre></blockquote>
66   *
67   * If there are no originating elements, none need to be passed.  This
68   * information may be used in an incremental environment to determine
69   * the need to rerun processors or remove generated files.
70   * Non-incremental environments may ignore the originating element
71   * information.
72   *
73   * <p> During each run of an annotation processing tool, a file with a
74   * given pathname may be created only once.  If that file already
75   * exists before the first attempt to create it, the old contents will
76   * be deleted.  Any subsequent attempt to create the same file during
77   * a run will throw a {@link FilerException}, as will attempting to
78   * create both a class file and source file for the same type name or
79   * same package name.  The {@linkplain Processor initial inputs} to
80   * the tool are considered to be created by the zeroth round;
81   * therefore, attempting to create a source or class file
82   * corresponding to one of those inputs will result in a {@link
83   * FilerException}.
84   *
85   * <p> In general, processors must not knowingly attempt to overwrite
86   * existing files that were not generated by some processor.  A {@code
87   * Filer} may reject attempts to open a file corresponding to an
88   * existing type, like {@code java.lang.Object}.  Likewise, the
89   * invoker of the annotation processing tool must not knowingly
90   * configure the tool such that the discovered processors will attempt
91   * to overwrite existing files that were not generated.
92   *
93   * <p> Processors can indicate a source or class file is generated by
94   * including an {@link javax.annotation.Generated @Generated}
95   * annotation.
96   *
97   * <p> Note that some of the effect of overwriting a file can be
98   * achieved by using a <i>decorator</i>-style pattern.  Instead of
99   * modifying a class directly, the class is designed so that either
100  * its superclass is generated by annotation processing or subclasses
101  * of the class are generated by annotation processing.  If the
102  * subclasses are generated, the parent class may be designed to use
103  * factories instead of public constructors so that only subclass
104  * instances would be presented to clients of the parent class.
105  *
106  * @author Joseph D. Darcy
107  * @author Scott Seligman
108  * @author Peter von der Ah&eacute;
109  * @version 1.10 06/08/28
110  * @since 1.6
111  */
112 public interface Filer {
113     /**
114      * Creates a new source file and returns an object to allow
115      * writing to it.  The file's name and path (relative to the
116      * {@linkplain StandardLocation#SOURCE_OUTPUT root output location
117      * for source files}) are based on the type to be declared in that
118      * file.  If more than one type is being declared, the name of the
119      * principal top-level type (the public one, for example) should
120      * be used.  A source file can also be created to hold information
121      * about a package, including package annotations.  To create a
122      * source file for a named package, have {@code name} be the
123      * package's name followed by {@code ".package-info"}; to create a
124      * source file for an unnamed package, use {@code "package-info"}.
125      * 
126      * <p> Note that to use a particular {@linkplain
127      * java.nio.charset.Charset charset} to encode the contents of the
128      * file, an {@code OutputStreamWriter} with the chosen charset can
129      * be created from the {@code OutputStream} from the returned
130      * object. If the {@code Writer} from the returned object is
131      * directly used for writing, its charset is determined by the
132      * implementation.  An annotation processing tool may have an
133      * {@code -encoding} flag or analogous option for specifying this;
134      * otherwise, it will typically be the platform's default
135      * encoding.
136      *
137      * <p>To avoid subsequent errors, the contents of the source file
138      * should be compatible with the {@linkplain
139      * ProcessingEnvironment#getSourceVersion source version} being used
140      * for this run.
141      *
142      * @param name  canonical (fully qualified) name of the principal type
143      *      being declared in this file or a package name followed by 
144      *          {@code ".package-info"} for a package information file
145      * @param originatingElements type or package elements causally
146      * associated with the creation of this file, may be elided or
147      * {@code null}
148      * @return a {@code JavaFileObject} to write the new source file
149      * @throws FilerException if the same pathname has already been
150      * created, the same type has already been created, or the name is
151      * not valid for a type
152      * @throws IOException if the file cannot be created
153      */
154     JavaFileObject createSourceFile(CharSequence   name,
155                     Element... originatingElements) throws IOException  ;
156 
157     /**
158      * Creates a new class file, and returns an object to allow
159      * writing to it.  The file's name and path (relative to the
160      * {@linkplain StandardLocation#CLASS_OUTPUT root output location
161      * for class files}) are based on the name of the type being
162      * written.  A class file can also be created to hold information
163      * about a package, including package annotations.  To create a
164      * class file for a named package, have {@code name} be the
165      * package's name followed by {@code ".package-info"}; creating a
166      * class file for an unnamed package is not supported.
167      *
168      * <p>To avoid subsequent errors, the contents of the class file
169      * should be compatible with the {@linkplain
170      * ProcessingEnvironment#getSourceVersion source version} being used
171      * for this run.
172      *
173      * @param name binary name of the type being written or a package name followed by 
174      *          {@code ".package-info"} for a package information file
175      * @param originatingElements type or package elements causally
176      * associated with the creation of this file, may be elided or
177      * {@code null}
178      * @return a {@code JavaFileObject} to write the new class file
179      * @throws FilerException if the same pathname has already been
180      * created, the same type has already been created, or the name is
181      * not valid for a type
182      * @throws IOException if the file cannot be created
183      */
184     JavaFileObject createClassFile(CharSequence   name,
185                    Element... originatingElements) throws IOException  ;
186 
187     /**
188      * Creates a new auxiliary resource file for writing and returns a
189      * file object for it.  The file may be located along with the
190      * newly created source files, newly created binary files, or
191      * other supported location.  The locations {@link
192      * StandardLocation#CLASS_OUTPUT CLASS_OUTPUT} and {@link
193      * StandardLocation#SOURCE_OUTPUT SOURCE_OUTPUT} must be
194      * supported.  The resource may be named relative to some package
195      * (as are source and class files), and from there by a relative
196      * pathname.  In a loose sense, the full pathname of the new file
197      * will be the concatenation of {@code location}, {@code pkg}, and
198      * {@code relativeName}.
199      *
200      * <p>Files created via this method are not registered for
201      * annotation processing, even if the full pathname of the file
202      * would correspond to the full pathname of a new source file
203      * or new class file.
204      * 
205      * @param location location of the new file
206      * @param pkg package relative to which the file should be named,
207      *      or the empty string if none
208      * @param relativeName final pathname components of the file
209      * @param originatingElements type or package elements causally
210      * associated with the creation of this file, may be elided or
211      * {@code null}
212      * @return a {@code FileObject} to write the new resource
213      * @throws IOException if the file cannot be created
214      * @throws FilerException if the same pathname has already been
215      * created
216      * @throws IllegalArgumentException for an unsupported location
217      * @throws IllegalArgumentException if {@code relativeName} is not relative
218      */
219    FileObject createResource(JavaFileManager.Location location,
220                  CharSequence   pkg,
221                  CharSequence   relativeName,
222                  Element... originatingElements) throws IOException  ;
223 
224     /**
225      * Returns an object for reading an existing resource.  The
226      * locations {@link StandardLocation#CLASS_OUTPUT CLASS_OUTPUT}
227      * and {@link StandardLocation#SOURCE_OUTPUT SOURCE_OUTPUT} must
228      * be supported.
229      *
230      * @param location location of the file
231      * @param pkg package relative to which the file should be searched,
232      *      or the empty string if none
233      * @param relativeName final pathname components of the file
234      * @return an object to read the file
235      * @throws FilerException if the same pathname has already been
236      * opened for writing
237      * @throws IOException if the file cannot be opened
238      * @throws IllegalArgumentException for an unsupported location
239      * @throws IllegalArgumentException if {@code relativeName} is not relative
240      */
241     FileObject getResource(JavaFileManager.Location location,
242                CharSequence   pkg,
243                CharSequence   relativeName) throws IOException  ;
244 }
245
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