手把手教你新建 jfinal 项目 （四）
使用缓存的好处很多，能够极大的提高页面显示速度。
1、准备好 jar包 ehcache.jar。并引入工程中。
2、jfinal主要提供了3中使用缓存的方法，这里主要说两种。
1）、注解使用法
java 注解 理解不多，个人觉得 注解其实就是 一个属性。例如给一个 test方法加了 @before 注解后，这个before 对象其实就成了 test 方法的一个属性，在调用 test时，可以获取到 这个 before 对象。
加了 注解后的的 index()：
public class WokersController extends Controller {
/**
* index 表示根路径，对应的路径为 localhost:..../hello
* 这里我们让它显示所有的工人。这里是使用了模板引擎 freeMark，它会根据list自动显示数据
*/
@Before(CacheInterceptor.class)//相当于给这个方法里面所有被 setAttr 的对象都添加到内存中
@CacheName("workers")//这个缓存的名字叫workers
public void index() {
List<Worker> list = Worker.dao.find("select * from worker where rownum<10");
//==request.setAttribute(name, value)，就是将list放入request中
setAttr("workersList", list);
//渲染到根路径下的workers.html页面中。
render("/workers.html");
}
看下 浏览器 请求的时间有没有变化。
不加缓存时的请求：
index 加了缓存后：
为什么加了这个注解后它会缓存。我们先来看看代码
//CacheInterceptor cacheData.put(name, request.getAttribute(name));//将request 中的对象加入缓存
@before ：
/** * Copyright (c) 2011-2014, James Zhan 詹波 ([email protected]). * * 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.jfinal.aop; import java.lang.annotation.ElementType; import java.lang.annotation.Inherited; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; /** * Before is used to configure Interceptor or Validator. */ @Inherited @Retention(RetentionPolicy.RUNTIME)//在程序运行时，也能获取到这个before @Target({ElementType.TYPE, ElementType.METHOD})//可以用在方法，类...上 public @interface Before { Class<? extends Interceptor>[] value();//有多个Interceptor的class } //也就是说，这个注解可以用在方法上，使用方法： @before（Interceptor1.class,Interceptor2.class）
我们使用的注解是@Before(CacheInterceptor.class)，我们看看CacheInterceptor
/** * Copyright (c) 2011-2014, James Zhan 詹波 ([email protected]). * * 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.jfinal.plugin.ehcache; import java.util.Enumeration; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Map.Entry; import java.util.Set; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; import javax.servlet.http.HttpServletRequest; import com.jfinal.aop.Interceptor; import com.jfinal.core.ActionInvocation; import com.jfinal.core.Controller; import com.jfinal.render.Render; /** * CacheInterceptor. */ public class CacheInterceptor implements Interceptor { private static final String renderKey = "$renderKey$"; private static volatile ConcurrentHashMap<String, ReentrantLock> lockMap = new ConcurrentHashMap<String, ReentrantLock>(); private ReentrantLock getLock(String key) { ReentrantLock lock = lockMap.get(key); if (lock != null) return lock; lock = new ReentrantLock(); ReentrantLock previousLock = lockMap.putIfAbsent(key, lock); return previousLock == null ? lock : previousLock; } /** 这个方法是关键，主要作用应该是将内存中的缓存直接给request了。该方法是在 过滤器JFinalFilter的 dofilter方法时被执行。下面我们在看下 dofilter 方法 */ final public void intercept(ActionInvocation ai) { Controller controller = ai.getController(); String cacheName = buildCacheName(ai, controller); String cacheKey = buildCacheKey(ai, controller); Map<String, Object> cacheData = CacheKit.get(cacheName, cacheKey); if (cacheData == null) { Lock lock = getLock(cacheName); lock.lock(); // prevent cache snowslide try { cacheData = CacheKit.get(cacheName, cacheKey); if (cacheData == null) { ai.invoke(); cacheAction(cacheName, cacheKey, controller); return ; } } finally { lock.unlock(); } } useCacheDataAndRender(cacheData, controller); } // TODO 考虑与 EvictInterceptor 一样强制使用 @CacheName private String buildCacheName(ActionInvocation ai, Controller controller) { CacheName cacheName = ai.getMethod().getAnnotation(CacheName.class); if (cacheName != null) return cacheName.value(); cacheName = controller.getClass().getAnnotation(CacheName.class); return (cacheName != null) ? cacheName.value() : ai.getActionKey(); } private String buildCacheKey(ActionInvocation ai, Controller controller) { StringBuilder sb = new StringBuilder(ai.getActionKey()); String urlPara = controller.getPara(); if (urlPara != null) sb.append("/").append(urlPara); String queryString = controller.getRequest().getQueryString(); if (queryString != null) sb.append("?").append(queryString); return sb.toString(); } private void cacheAction(String cacheName, String cacheKey, Controller controller) { HttpServletRequest request = controller.getRequest(); Map<String, Object> cacheData = new HashMap<String, Object>(); for (Enumeration<String> names=request.getAttributeNames(); names.hasMoreElements();) { String name = names.nextElement(); cacheData.put(name, request.getAttribute(name)); } cacheData.put(renderKey, controller.getRender()); // cache render CacheKit.put(cacheName, cacheKey, cacheData); } private void useCacheDataAndRender(Map<String, Object> cacheData, Controller controller) { HttpServletRequest request = controller.getRequest(); Set<Entry<String, Object>> set = cacheData.entrySet(); for (Iterator<Entry<String, Object>> it=set.iterator(); it.hasNext();) { Entry<String, Object> entry = it.next(); request.setAttribute(entry.getKey(), entry.getValue()); } request.removeAttribute(renderKey); controller.render((Render)cacheData.get(renderKey)); // set render from cacheData } }
//JFinalFilter类
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest)req;
HttpServletResponse response = (HttpServletResponse)res;
request.setCharacterEncoding(encoding);
String target = request.getRequestURI();
if (contextPathLength != 0)
target = target.substring(contextPathLength);
boolean[] isHandled = {false};
try {
//执行到这里
handler.handle(target, request, response, isHandled);
}
catch (Exception e) {
if (log.isErrorEnabled()) {
String qs = request.getQueryString();
log.error(qs == null ? target : target + "?" + qs, e);
}
}
if (isHandled[0] == false)
chain.doFilter(request, response);
}
//ActionHandler类
public final void handle(String target, HttpServletRequest request, HttpServletResponse response, boolean[] isHandled) {
if (target.indexOf(".") != -1) {
return ;
}
isHandled[0] = true;
String[] urlPara = {null};
Action action = actionMapping.getAction(target, urlPara);
if (action == null) {
if (log.isWarnEnabled()) {
String qs = request.getQueryString();
log.warn("404 Action Not Found: " + (qs == null ? target : target + "?" + qs));
}
renderFactory.getErrorRender(404).setContext(request, response).render();
return ;
}
try {
Controller controller = action.getControllerClass().newInstance();
controller.init(request, response, urlPara[0]);
if (devMode) {
boolean isMultipartRequest = ActionReporter.reportCommonRequest(controller, action);
new ActionInvocation(action, controller).invoke();
if (isMultipartRequest) ActionReporter.reportMultipartRequest(controller, action);
}
else {
//执行到这里
new ActionInvocation(action, controller).invoke();
}
Render render = controller.getRender();
if (render instanceof ActionRender) {
String actionUrl = ((ActionRender)render).getActionUrl();
if (target.equals(actionUrl))
throw new RuntimeException("The forward action url is the same as before.");
else
handle(actionUrl, request, response, isHandled);
return ;
}
if (render == null)
render = renderFactory.getDefaultRender(action.getViewPath() + action.getMethodName());
render.setContext(request, response, action.getViewPath()).render();
}
catch (RenderException e) {
if (log.isErrorEnabled()) {
String qs = request.getQueryString();
log.error(qs == null ? target : target + "?" + qs, e);
}
}
catch (ActionException e) {
int errorCode = e.getErrorCode();
if (errorCode == 404 && log.isWarnEnabled()) {
String qs = request.getQueryString();
log.warn("404 Not Found: " + (qs == null ? target : target + "?" + qs));
}
else if (errorCode == 401 && log.isWarnEnabled()) {
String qs = request.getQueryString();
log.warn("401 Unauthorized: " + (qs == null ? target : target + "?" + qs));
}
else if (errorCode == 403 && log.isWarnEnabled()) {
String qs = request.getQueryString();
log.warn("403 Forbidden: " + (qs == null ? target : target + "?" + qs));
}
else if (log.isErrorEnabled()) {
String qs = request.getQueryString();
log.error(qs == null ? target : target + "?" + qs, e);
}
e.getErrorRender().setContext(request, response).render();
}
catch (Exception e) {
if (log.isErrorEnabled()) {
String qs = request.getQueryString();
log.error(qs == null ? target : target + "?" + qs, e);
}
renderFactory.getErrorRender(500).setContext(request, response).render();
}
}
//ActionInvocation
/**
* Invoke the action.
*/
public void invoke() {
if (index < inters.length)
inters[index++].intercept(this);//执行每个 Interceptor的intercept 方法，刚刚那个缓存类
//，就执行了在缓存中读数据的操作
else if (index++ == inters.length) // index++ ensure invoke action only one time
// try {action.getMethod().invoke(controller, NULL_ARGS);} catch (Exception e) {throw new RuntimeException(e);}
try {
action.getMethod().invoke(controller, NULL_ARGS);
}
catch (InvocationTargetException e) {
Throwable cause = e.getTargetException();
if (cause instanceof RuntimeException)
throw (RuntimeException)cause;
throw new RuntimeException(e);
}
catch (RuntimeException e) {
throw e;
}
catch (Exception e) {
throw new RuntimeException(e);
}
}
我们理清思路：
页面请求到来---》进入 filter 的dofilter 方法,并获取注解中的Interceptor--》执行Interceptor中的方法，从缓存中直接获取数据--》最后返回前端。
这个过程中并没有继续查询数据库，所以速度要快，就是消耗一些内存。
@Before(EvictInterceptor.class) 是作为清空缓存使用的，可以自己去看看。
2）、使用 CacheKit来管理缓存，代码为
index 方法
//这个方法的意思是如果存在缓存就使用缓存，没有缓存就去 查询数据库。应该比较容易理解
List<Record> list = CacheKit.get("workers", "workersList", new
IDataLoader(){
public Object load() {
return Db.find("select * from worker");
}});
setAttr("workersList", list);
//渲染到根路径下的workers.html页面中。
render("/workers.html");