JAVA快取有兩種:
一、檔案快取,是指把數據存儲在磁碟上，可以xml格式，也可以序列化檔案DAT格式還是其它檔案格式。
二、記憶體快取，也就是實現一個類中靜態Map,對這個Map進行常規的增刪查。
其代碼如下：
Cache類
public class Cache {
private String key;//快取ID
private Object value;//快取數據
private long timeOut;//更新時間
private boolean expired; //是否終止
public Cache() {
super();
}
public Cache(String key, Object value, long timeOut, boolean expired) {
this.key = key;
this.value = value;
this.timeOut = timeOut;
this.expired = expired;
}
public String getKey() {
return key;
}
public long getTimeOut() {
return timeOut;
}
public Object getValue() {
return value;
}
public void setKey(String string) {
key = string;
}
public void setTimeout(long l) {
timeOut = l;
}
public void setValue(Object object) {
value = object;
}
public boolean isExpired() {
return expired;
}
public void setExpired(boolean b) {
expired = b;
}
}
//測試類，
class Test {
public static void main(String[] args) {
System.out.println(CacheManager.getSimpleFlag("alksd"));
// CacheManager.putCache("abc", new Cache());
// CacheManager.putCache("def", new Cache());
// CacheManager.putCache("ccc", new Cache());
// CacheManager.clearOnly("");
// Cache c = new Cache();
// for (int i = 0; i < 10; i++) {
// CacheManager.putCache("" + i, c);
// }
// CacheManager.putCache("aaaaaaaa", c);
// CacheManager.putCache("abchcy;alskd", c);
// CacheManager.putCache("cccccccc", c);
// CacheManager.putCache("abcoqiwhcy", c);
// System.out.println("刪除前的大小："+CacheManager.getCacheSize());
// CacheManager.getCacheAllkey();
// CacheManager.clearAll("aaaa");
// System.out.println("刪除後的大小："+CacheManager.getCacheSize());
// CacheManager.getCacheAllkey();
}
}
CacheManager類
public class CacheManager {private static HashMap cacheMap = new HashMap();
//單實例構造方法
private CacheManager() {
super();
}
//獲取布爾值的快取
public static boolean getSimpleFlag(String key){
try{
return (Boolean) cacheMap.get(key);
}catch(NullPointerException e){
return false;
}
}
public static long getServerStartdt(String key){
try {
return (Long)cacheMap.get(key);
} catch (Exception ex) {
return 0;
}
}
//設定布爾值的快取
public synchronized static boolean setSimpleFlag(String key,boolean flag){
if (flag && getSimpleFlag(key)) {//假如為真不允許被覆蓋
return false;
}else{
cacheMap.put(key, flag);
return true;
}
}
public synchronized static boolean setSimpleFlag(String key,long serverbegrundt){
if (cacheMap.get(key) == null) {
cacheMap.put(key,serverbegrundt);
return true;
}else{
return false;
}
}
//得到快取。同步靜態方法
private synchronized static Cache getCache(String key) {
return (Cache) cacheMap.get(key);
}
//判斷是否存在一個快取
private synchronized static boolean hasCache(String key) {
return cacheMap.containsKey(key);
}
//清除所有快取
public synchronized static void clearAll() {
cacheMap.clear();
}
//清除某一類特定快取,通過遍歷HASHMAP下的所有對象，來判斷它的KEY與傳入的TYPE是否匹配
public synchronized static void clearAll(String type) {
Iterator i = cacheMap.entrySet().iterator();
String key;
ArrayList arr = new ArrayList();
try {
while (i.hasNext()) {
java.util.Map.Entry entry = (java.util.Map.Entry) i.next();
key = (String) entry.getKey();
if (key.startsWith(type)) { //如果匹配則刪除掉
arr.add(key);
}
}
for (int k = 0; k < arr.size(); k++) {
clearOnly(arr.get(k));
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
//清除指定的快取
public synchronized static void clearOnly(String key) {
cacheMap.remove(key);
}
//載入快取
public synchronized static void putCache(String key, Cache obj) {
cacheMap.put(key, obj);
}
//獲取快取信息
public static Cache getCacheInfo(String key) {
if (hasCache(key)) {
CACHE CACHE = getCache(key);
if (cacheExpired(cache)) { //調用判斷是否終止方法
cache.setExpired(true);
}
return cache;
}else
return null;
}
//載入快取信息
public static void putCacheInfo(String key, Cache obj, long dt,boolean expired) {
Cache cache = new Cache();
cache.setKey(key);
cache.setTimeOut(dt + System.currentTimeMillis()); //設定多久後更新快取
cache.setValue(obj);
cache.setExpired(expired); //快取默認載入時，終止狀態為FALSE
cacheMap.put(key, cache);
}
//重寫載入快取信息方法
public static void putCacheInfo(String key,Cache obj,long dt){
Cache cache = new Cache();
cache.setKey(key);
cache.setTimeOut(dt+System.currentTimeMillis());
cache.setValue(obj);
cache.setExpired(false);
cacheMap.put(key,cache);
}
//判斷快取是否終止
public static boolean cacheExpired(Cache cache) {
if (null == cache) { //傳入的快取不存在
return false;
}
long nowDt = System.currentTimeMillis(); //系統當前的毫秒數
long cacheDt = cache.getTimeOut(); //快取內的過期毫秒數
if (cacheDt <= 0||cacheDt>nowDt) { //過期時間小於等於零時,或者過期時間大於當前時間時，則為FALSE
return false;
} else { //大於過期時間 即過期
return true;
}
}
//獲取快取中的大小
public static int getCacheSize() {
return cacheMap.size();
}
//獲取指定的類型的大小
public static int getCacheSize(String type) {
int k = 0;
Iterator i = cacheMap.entrySet().iterator();
String key;
try {
while (i.hasNext()) {
java.util.Map.Entry entry = (java.util.Map.Entry) i.next();
key = (String) entry.getKey();
if (key.indexOf(type) != -1) { //如果匹配則刪除掉
k++;
}
}
} catch (Exception ex) {
ex.printStackTrace();
}
return k;
}
//獲取快取對象中的所有鍵值名稱
public static ArrayList getCacheAllkey() {
ArrayList a = new ArrayList();
try {
Iterator i = cacheMap.entrySet().iterator();
while (i.hasNext()) {
java.util.Map.Entry entry = (java.util.Map.Entry) i.next();
a.add((String) entry.getKey());
}
} catch (Exception ex) {} finally {
return a;
}
}
//獲取快取對象中指定類型 的鍵值名稱
public static ArrayList getCacheListkey(String type) {
ArrayList a = new ArrayList();
String key;
try {
Iterator i = cacheMap.entrySet().iterator();
while (i.hasNext()) {
java.util.Map.Entry entry = (java.util.Map.Entry) i.next();
key = (String) entry.getKey();
if (key.indexOf(type) != -1) {
a.add(key);
}
}
} catch (Exception ex) {} finally {
return a;
}
}
}
