差異處

這裏顯示兩個版本的差異處。

--- java:guava:cache:helloworld [2016/04/13 13:40]
tony 建立
+++ java:guava:cache:helloworld [2023/06/25 09:48] (目前版本)
@@ 行 1: / 行 1: @@
 {{tag>java guava}}
 ====== Guava Cache Hello World ======
+===== Introduction =====
+大部分應用程式都會透過Cache機制，去增加效能或暫時性的備援。Guava提供了簡單的Cache實做，讓你不用替資源回收或同步問題煩惱。
 ===== How to? =====
+我們可以透過CacheBuilder去設定Cache的條件。在build時，你可以選擇要預先提供服務實做(CacheLoader)，或是在get時提供。以下是在build時，就提供了服務實做:
 <code java>
-package org.tonylin.practice.guava.cache;
+@Test
+public void test() throws Exception {
-import java.util.concurrent.TimeUnit;
+	LoadingCache<String, String> cache =  CacheBuilder.newBuilder()
+	.maximumSize(10)
-import org.junit.Assert;
+	.expireAfterAccess(5, TimeUnit.SECONDS)
-import org.junit.Test;
+	.expireAfterWrite(5, TimeUnit.SECONDS)
+	.softValues()
-import com.google.common.cache.CacheBuilder;
+	.build(new CacheLoader<String, String>(){
-import com.google.common.cache.CacheLoader;
+		private int count = 0;
-import com.google.common.cache.LoadingCache;
+		@Override
+		public String load(String key) throws Exception {
-public class TestCache {
+			return key + (count++);
+		}
-	@Test
+	});
-	public void test() throws Exception {
-		LoadingCache<String, String> cache =  CacheBuilder.newBuilder()
-		.maximumSize(10)
-		.expireAfterAccess(5, TimeUnit.SECONDS)
-		.expireAfterWrite(5, TimeUnit.SECONDS)
-		.softValues()
-		.build(new CacheLoader<String, String>(){
-			private int count = 0;
-			@Override
-			public String load(String key) throws Exception {
-				return key + (count++);
-			}
-		});
-		Assert.assertEquals("test10", cache.get("test1"));
+	Assert.assertEquals("test10", cache.get("test1"));
-		Thread.sleep(4000);
+	Thread.sleep(4000);
-		Assert.assertEquals("test10", cache.get("test1"));
+	Assert.assertEquals("test10", cache.get("test1"));
-		Thread.sleep(2000);
+	Thread.sleep(2000);
-		Assert.assertNull(cache.getIfPresent("test1"));
+	Assert.assertNull(cache.getIfPresent("test1"));
-		Assert.assertEquals("test11", cache.get("test1"));
+	Assert.assertEquals("test11", cache.get("test1"));
-	}
 }
 </code>
+在get時才能決定實做:
+<code java>
+@Test
+public void testCache() throws Exception {
+	Cache<String, String> cache =  CacheBuilder.newBuilder()
+	.maximumSize(10)
+	.expireAfterAccess(5, TimeUnit.SECONDS)
+	.expireAfterWrite(5, TimeUnit.SECONDS)
+	.softValues()
+	.build();
+	Assert.assertEquals("0", cache.get("test1", ()->{return "0";}));
+	Thread.sleep(4000);
+	Assert.assertEquals("0", cache.get("test1", ()->{return "1";}));
+	Thread.sleep(2000);
+	Assert.assertNull(cache.getIfPresent("test1"));
+	Assert.assertEquals("2", cache.get("test1", ()->{return "2";}));
+}
+</code>
+從範例可以得知，在cache過期前，都不會實際去執行服務取得內容。
 =====  =====
 ----
 \\
 ~~DISQUS~~