Directory


1   package org.apache.lucene.store;
2   
3   /**
4    * Copyright 2004 The Apache Software Foundation
5    *
6    * Licensed under the Apache License, Version 2.0 (the "License");
7    * you may not use this file except in compliance with the License.
8    * You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  import java.io.IOException  ;
20  
21  /** A Directory is a flat list of files.  Files may be written once, when they
22   * are created.  Once a file is created it may only be opened for read, or
23   * deleted.  Random access is permitted both when reading and writing.
24   *
25   * <p> Java's i/o APIs not used directly, but rather all i/o is
26   * through this API.  This permits things such as: <ul>
27   * <li> implementation of RAM-based indices;
28   * <li> implementation indices stored in a database, via JDBC;
29   * <li> implementation of an index as a single file;
30   * </ul>
31   *
32   * @author Doug Cutting
33   */
34  public abstract class Directory {
35    /** Returns an array of strings, one for each file in the directory. */
36    public abstract String  [] list()
37         throws IOException  ;
38  
39    /** Returns true iff a file with the given name exists. */
40    public abstract boolean fileExists(String   name)
41         throws IOException  ;
42  
43    /** Returns the time the named file was last modified. */
44    public abstract long fileModified(String   name)
45         throws IOException  ;
46  
47    /** Set the modified time of an existing file to now. */
48    public abstract void touchFile(String   name)
49         throws IOException  ;
50  
51    /** Removes an existing file in the directory. */
52    public abstract void deleteFile(String   name)
53         throws IOException  ;
54  
55    /** Renames an existing file in the directory.
56      If a file already exists with the new name, then it is replaced.
57      This replacement should be atomic. */
58    public abstract void renameFile(String   from, String   to)
59         throws IOException  ;
60  
61    /** Returns the length of a file in the directory. */
62    public abstract long fileLength(String   name)
63         throws IOException  ;
64  
65    /** @deprecated use {@link #createOutput(String)} */
66    public OutputStream createFile(String   name) throws IOException   {
67      return (OutputStream)createOutput(name);
68    }
69  
70    /** Creates a new, empty file in the directory with the given name.
71        Returns a stream writing this file. */
72    public IndexOutput createOutput(String   name) throws IOException   {
73      // default implementation for back compatibility
74      // this method should be abstract
75      return (IndexOutput)createFile(name);
76    }
77  
78    /** @deprecated use {@link #openInput(String)} */
79    public InputStream openFile(String   name) throws IOException   {
80      return (InputStream)openInput(name);
81    }
82  
83    /** Returns a stream reading an existing file. */
84    public IndexInput openInput(String   name)
85      throws IOException   {
86      // default implementation for back compatibility
87      // this method should be abstract
88      return (IndexInput)openFile(name);
89    }
90  
91    /** Construct a {@link Lock}.
92     * @param name the name of the lock file
93     */
94    public abstract Lock makeLock(String   name);
95  
96    /** Closes the store. */
97    public abstract void close()
98         throws IOException  ;
99  }
100
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