/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.volley;
import java.util.Collections;
import java.util.Map;
/**
* An interface for a cache keyed by a String with a byte array as data.
*/
/*
* 缓存的接口
* 提供一些接口方法需要是钱
* 全 Volley 中主要实现了一个 DiskBasedCache
*/
public interface Cache {
/**
* Retrieves an entry from the cache.
*
* @param key Cache key
* @return An {@link Entry} or null in the event of a cache miss
*/
// 获取 缓存的 Response 数据
public Entry get(String key);
/**
* Adds or replaces an entry to the cache.
*
* @param key Cache key
* @param entry Data to store and metadata for cache coherency, TTL, etc.
*/
// 存放 需要缓存的 Response 数据
public void put(String key, Entry entry);
/**
* Performs any potentially long-running actions needed to initialize the cache;
* will be called from a worker thread.
*/
/*
* 初始化缓存操作
* 实现该接口的缓存,初始化操作时都需要做一些事情
* 比如 DiskBasedCache.initialize() 初始化时,
* 1.对文件目录以及文件进行了检查
* 2.扫描目录中文件,得到所有缓存数据信息放入内存中
*/
public void initialize();
/**
* Invalidates an entry in the cache.
*
* @param key Cache key
* @param fullExpire True to fully expire the entry, false to soft expire
*/
/*
* 放一条缓存数据 无效
* 默认情况是 把 过期时间=0
* fullExpire=true 的话 刷新时间=0 要刷新
* fullExpire=false 的话 刷新时间=不变 需要判断是否小于当前时间 小于则刷新
*/
public void invalidate(String key, boolean fullExpire);
/**
* Removes an entry from the cache.
*
* @param key Cache key
*/
// 移除某条缓存
public void remove(String key);
/**
* Empties the cache.
*/
// 清空整个缓存
public void clear();
/**
* Data and metadata for an entry returned by the cache.
*/
/*
* 用于缓存 Response 数据
*/
public static class Entry {
/** The data returned from cache. */
// 缓存 Response contents
public byte[] data;
/** ETag for cache coherency. */
// 缓存 Response Header "ETag"
public String etag;
/** Date of this response as reported by the server. */
// 缓存 Response Header "Date"
public long serverDate;
/** The last modified date for the requested object. */
// 缓存 Response Header Last-Modified
public long lastModified;
/** TTL for this record. */
// 缓存 计算好的 过期时间
public long ttl;
/** Soft TTL for this record. */
// 缓存 计算好的 刷新时间
public long softTtl;
/** Immutable response headers as received from server; must be non-null. */
// 缓存 Response 对应的 Request Header 数据
public Map<String, String> responseHeaders = Collections.emptyMap();
/** True if the entry is expired. */
// 判断是否过期
public boolean isExpired() {
return this.ttl < System.currentTimeMillis();
}
/** True if a refresh is needed from the original data source. */
// 判断是否需要刷新
public boolean refreshNeeded() {
/*
* 由此可知
* softTtl 是一个 刷新时间
* 如果小于了当前当前时间 就刷新
*/
return this.softTtl < System.currentTimeMillis();
}
}
}