1 /*
2  * Copyright (C) 2011 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.android.volley;
18 
19 import java.util.Collections;
20 import java.util.Map;
21 
22 /**
23  * An interface for a cache keyed by a String with a byte array as data.
24  */
25 public interface Cache {
26     /**
27      * Retrieves an entry from the cache.
28      * @param key Cache key
29      * @return An {@link Entry} or null in the event of a cache miss
30      */
get(String key)31     public Entry get(String key);
32 
33     /**
34      * Adds or replaces an entry to the cache.
35      * @param key Cache key
36      * @param entry Data to store and metadata for cache coherency, TTL, etc.
37      */
put(String key, Entry entry)38     public void put(String key, Entry entry);
39 
40     /**
41      * Performs any potentially long-running actions needed to initialize the cache;
42      * will be called from a worker thread.
43      */
initialize()44     public void initialize();
45 
46     /**
47      * Invalidates an entry in the cache.
48      * @param key Cache key
49      * @param fullExpire True to fully expire the entry, false to soft expire
50      */
invalidate(String key, boolean fullExpire)51     public void invalidate(String key, boolean fullExpire);
52 
53     /**
54      * Removes an entry from the cache.
55      * @param key Cache key
56      */
remove(String key)57     public void remove(String key);
58 
59     /**
60      * Empties the cache.
61      */
clear()62     public void clear();
63 
64     /**
65      * Data and metadata for an entry returned by the cache.
66      */
67     public static class Entry {
68         /** The data returned from cache. */
69         public byte[] data;
70 
71         /** ETag for cache coherency. */
72         public String etag;
73 
74         /** Date of this response as reported by the server. */
75         public long serverDate;
76 
77         /** The last modified date for the requested object. */
78         public long lastModified;
79 
80         /** TTL for this record. */
81         public long ttl;
82 
83         /** Soft TTL for this record. */
84         public long softTtl;
85 
86         /** Immutable response headers as received from server; must be non-null. */
87         public Map<String, String> responseHeaders = Collections.emptyMap();
88 
89         /** True if the entry is expired. */
isExpired()90         public boolean isExpired() {
91             return this.ttl < System.currentTimeMillis();
92         }
93 
94         /** True if a refresh is needed from the original data source. */
refreshNeeded()95         public boolean refreshNeeded() {
96             return this.softTtl < System.currentTimeMillis();
97         }
98     }
99 
100 }
101