1 模式概要
1.1 简介
- 责任链模式为请求创建一个接收者对象链,每个接收者都包含对另一个接收者的引用,如果一个对象不能处理该请求,那么它会把请求传给下一个接收者,依此类推
- 责任链模式避免了请求的发送者和接收者耦合在一起,让多个对象都有可能接收请求,将这些对象连成一条链,并且沿着这条链传递请求,直到有对象处理它为止
1.2 责任链模式优缺点
优点 >降低耦合度。它将请求的发送者和接收者解耦 简化了对象,使得对象不需要知道链的结构 增强给对象指派职责的灵活性,允许动态地新增或者删除责任链 增加新的请求处理类方便
缺点 >不能保证请求一定被接收; 系统性能将受到一定影响,调试时不方便,可能会造成循环调用
2 模式结构
2.1 对象定义
*Handler(抽象处理者)*: 定义一个处理请求的接口,提供对后续处理者的引用 *ConcreteHandler(具体处理者)*: 抽象处理者的子类,处理用户请求,可选将请求处理掉还是传给下家;在具体处理者中可以访问链中下一个对象,以便请求的转发
2.2 类图及设计
代码详解:
抽象处理者
public abstract class Handler {
protected Handler nextHandler; // 下一个责任链成员
public Handler getNextHandler() {
return nextHandler;
}
public void setNextHandler(Handler nextHandler) {
this.nextHandler = nextHandler;
}
// 处理传递过来的时间
public abstract void handleMessage(int type);
}
具体处理者 在当前处理者对象无法处理时,将执行权传给下一个处理者对象
:::java
public class ConcreteHandler1 extends Handler {
@Override
public void handleMessage(int type) {
if (type == 1 || type == 3) {
System.out.println("ConcreteHandler1解决了问题!");
} else {
System.out.println("ConcreteHandler1解决不了问题......");
if (nextHandler != null) {
nextHandler.handleMessage(type);
} else {
System.out.println("没有人能处理这个消息");
}
}
}
}
public class ConcreteHandler2 extends Handler {
@Override
public void handleMessage(int type) {
if (type == 2 || type == 5) {
System.out.println("ConcreteHandler2解决了问题!");
} else {
System.out.println("ConcreteHandler2解决不了问题......");
if (nextHandler != null) {
nextHandler.handleMessage(type);
} else {
System.out.println("没有人能处理这个消息");
}
}
}
}
public class ConcreteHandler3 extends Handler {
@Override
public void handleMessage(int type) {
if (type == 4 || type == 6) {
System.out.println("ConcreteHandler3解决了问题!");
} else {
System.out.println("ConcreteHandler3解决不了问题......");
if (nextHandler != null) {
nextHandler.handleMessage(type);
} else {
System.out.println("没有人能处理这个消息");
}
}
}
}
Client 客户端调用
// 初始化责任链:handler1 -> handler2 -> handler3
Handler handler1 = new ConcreteHandler1();
Handler handler2 = new ConcreteHandler2();
Handler handler3 = new ConcreteHandler3();
handler2.setNextHandler(handler3);
handler1.setNextHandler(handler2);
// 处理事件
System.out.println("--------------Message1");
handler1.handleMessage(1);
System.out.println("--------------Message2");
handler1.handleMessage(2);
System.out.println("--------------Message3");
handler1.handleMessage(4);
System.out.println("--------------Message4");
handler1.handleMessage(7);
从上述模式可以知道,当我们需要多个ifelse
做逻辑判断的时候,可以引入,从而提高代码可维护性
2.3 适用场景:
- 有多个对象可以处理同一个请求,具体哪个对象处理该请求由运行时刻自动确定
- 在不明确指定接收者的情况下,向多个对象中的某一个对象提交一个请求
- 可动态指定一组对象的处理请求
3 Spring中的过滤器
我们来分析Spring中Filter的加载流程和执行流程
3.1 初始化流程
初始化过滤器加载数据流如下:
关键性代码
public void onStartup(ServletContext servletContext) throws ServletException {
Filter filter = getFilter();
Assert.notNull(filter, "Filter must not be null");
String name = getOrDeduceName(filter);
if (!isEnabled()) {
this.logger.info("Filter " + name + " was not registered (disabled)");
return;
}
//增加过滤器,数据流向 HashMap<String, FilterDef> filterDefs
FilterRegistration.Dynamic added = servletContext.addFilter(name, filter);
if (added == null) {
this.logger.info("Filter " + name + " was not registered "
+ "(possibly already registered?)");
return;
}
//配置过滤器注册信息
configure(added);
}
configure()
方法主要关注
if (isMatchAfter) {
context.addFilterMap(filterMap);
} else {
context.addFilterMapBefore(filterMap);
}
不管是数据走哪里,最终会通过 System.arraycopy 数组扩容,增加过滤器信息到 private FilterMap[] array
这个数组中。
最后调用StandardContext类中的 filterStart()
方法完成过滤器的初始化
3.2 执行过程
主要分两步,创建过滤器责任链 和 执行责任链
3.2.1 创建过程
创建filterChain方法主要在ApplicationFilterFactory.createFilterChain(request, wrapper, servlet)
中,部分代码讲解:
{
// 获取过滤器上下文
StandardContext context = (StandardContext) wrapper.getParent();
//获取加载的过滤器列表
FilterMap filterMaps[] = context.findFilterMaps();
// If there are no filter mappings, we are done
if ((filterMaps == null) || (filterMaps.length == 0))
return (filterChain);
// 获取匹配的过滤器映射信息
DispatcherType dispatcher =
(DispatcherType) request.getAttribute(Globals.DISPATCHER_TYPE_ATTR);
String requestPath = null;
Object attribute = request.getAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR);
if (attribute != null){
requestPath = attribute.toString();
}
String servletName = wrapper.getName();
// 每个过滤器配置对应处理的请求路径信息
for (int i = 0; i < filterMaps.length; i++) {
if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
continue;
}
if (!matchFiltersURL(filterMaps[i], requestPath))
continue;
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMaps[i].getFilterName());
if (filterConfig == null) {
// FIXME - log configuration problem
continue;
}
filterChain.addFilter(filterConfig);
}
// 配置对应servletName信息,最后返回过滤器链
for (int i = 0; i < filterMaps.length; i++) {
if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
continue;
}
if (!matchFiltersServlet(filterMaps[i], servletName))
continue;
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMaps[i].getFilterName());
if (filterConfig == null) {
// FIXME - log configuration problem
continue;
}
filterChain.addFilter(filterConfig);
}
// Return the completed filter chain
return filterChain;
}
在StandardWrapperValue类的invoke()
方法中调用ApplicationFilterChai类的createFilterChain()
方法
在ApplicationFilterChai类的createFilterChain()
方法中调用ApplicationFilterChain类的addFilter()
方法
在ApplicationFilterChain类的addFilter()
方法中给ApplicationFilterConfig数组赋值
3.2.2 执行责任链
调用ApplicationFilterChain的 doFilter()
方法中最后会调用一个internalDoFilter()
方法,目的就是执行ApplicationFilterChain中的全部过滤器,从代码中可以发现它调用了 doFilter
,而在 doFilter
又会调用internalDoFilter
从而使所有Filter都得以调用
private void internalDoFilter(ServletRequest request,ServletResponse response) throws IOException, ServletException {
// 如果存在下一个,继续调用下一个过滤器
if (pos < n) {
ApplicationFilterConfig filterConfig = filters[pos++];
try {
Filter filter = filterConfig.getFilter();
if (request.isAsyncSupported() && "false".equalsIgnoreCase(
filterConfig.getFilterDef().getAsyncSupported())) {
request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
}
if( Globals.IS_SECURITY_ENABLED ) {
final ServletRequest req = request;
final ServletResponse res = response;
Principal principal =
((HttpServletRequest) req).getUserPrincipal();
Object[] args = new Object[]{req, res, this};
SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);
} else {
// 此处调用Filter的doFilter()方法 / 而 doFilter 又会调用 internalDoFilter 直到调用完所有的过滤器
filter.doFilter(request, response, this);
}
} catch (IOException | ServletException | RuntimeException e) {
throw e;
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("filterChain.filter"), e);
}
return;
}
// 从最后一个开始调用
try {
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(request);
lastServicedResponse.set(response);
}
if (request.isAsyncSupported() && !servletSupportsAsync) {
request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
Boolean.FALSE);
}
// 包装请求
if ((request instanceof HttpServletRequest) &&
(response instanceof HttpServletResponse) &&
Globals.IS_SECURITY_ENABLED ) {
final ServletRequest req = request;
final ServletResponse res = response;
Principal principal =
((HttpServletRequest) req).getUserPrincipal();
Object[] args = new Object[]{req, res};
SecurityUtil.doAsPrivilege("service", servlet, classTypeUsedInService,args, principal);
} else {
servlet.service(request, response);
}
} catch (IOException | ServletException | RuntimeException e) {
throw e;
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("filterChain.servlet"), e);
} finally {
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(null);
lastServicedResponse.set(null);
}
}
}
这样,一个完整的过滤器链就形成,然后进行调用
4 项目中的实际运用
业务场景
我们在项目中使用了阿里的MQ消息中间件,来加快请求的响应时间和异步解耦处理。RocktMQ主要可以按Topic来分区,然后按Tag分组,不同的业务区分不同的tag
比如:
短信类的消息 messageTag
手机推送消息 pushTag
延时任务消息 delayTag
等等。。。
常规写法
if(message.getTag() == messageTag){
//doSomething
}else if(message.getTag() == pushTag){
//doSomething
}else if (message.getTag() == delayTag){
//doSomething
}
....
要是ifelse
多了,最后会形成箭头代码,最后连自己都不知道逻辑了。所以我就想到了责任链模式,刚好符合我们的实际场景。
具体设计方案如下:
设计UML类图
*抽象公共监听器*,主要用到了单例模式获取常量
public abstract class AbstractCommonListener {
private ParametersDO parametersDO;
protected AbstractCommonListener() {
//获取单例对象
this.parametersDO = ParametersDO.getInstance();
}
public final String getAccessKey() {
return parametersDO.getAccessKey();
}
public final String getSecretKey() {
return parametersDO.getSecretKey();
}
public final String getConsumerId() {
return parametersDO.getConsumerId();
}
public final String getONSAddr() {
return parametersDO.getONSAddr();
}
public final String getTopic() {
return parametersDO.getTopic();
}
}
class ParametersDO{
private static volatile boolean initialize = false;
private String accessKey;
private String secretKey;
private String consumerId;
private String ONSAddr;
private String topic;
private ParametersDO() {
synchronized (ParametersDO.class) {
if (!initialize) {
this.accessKey = BundleUtil.getResult("mq.accesskey");
this.consumerId = BundleUtil.getResult("mq.public.consumer.id");
this.ONSAddr = BundleUtil.getResult("mq.ons.addr");
this.topic = BundleUtil.getResult("mq.public.topic");
this.secretKey = BundleUtil.getResult("mq.secretkey");
initialize = !initialize;
} else {
throw new RuntimeException("ParametersDO单例已被破坏");
}
}
}
static ParametersDO getInstance() {
return ListenerHolder.INSTANCE;
}
private static class ListenerHolder{
private static final ParametersDO INSTANCE = new ParametersDO();
}
final String getAccessKey() {
return accessKey;
}
final String getSecretKey() {
return secretKey;
}
final String getConsumerId() {
return consumerId;
}
final String getONSAddr() {
return ONSAddr;
}
final String getTopic() {
return topic;
}
}
*具体监听器*,监听器主要用于MQ监听消费Topic
public class GlobalOrderListener extends AbstractCommonListener implements MessageOrderListener {
@Override
public OrderAction consume(Message message, ConsumeOrderContext context) {
//新增处理消费tag 只需添加Handler
AbstractMessageHandler<OrderAction, Message> handler = HandlerFactory.getHandlerResponsibilityChain(
JpushOrderHandler.class,
DelayRemoveOrderHandler.class);
return handler.handleMessage(message);
}
}
正常情况下,我们会在consume()
方法中区分tag来做不同业务的数据处理
抽象处理者
/**
* @author nicky_chin [shuilianpiying@163.com]
* @since --created on 2018/6/26 at 14:42
* 责任链抽象类
*/
public abstract class AbstractMessageHandler<T, R> extends AbstractCommonListener {
/**
* 下一个责任链成员
*/
protected AbstractMessageHandler<T, R> nextHandler;
public AbstractMessageHandler getNextHandler() {
return nextHandler;
}
public void setNextHandler(AbstractMessageHandler<T, R> nextHandler) {
this.nextHandler = nextHandler;
}
/**
* 处理传递过来的tag
* @param message 表达式
* @return T
*/
public abstract T handleMessage(R message);
}
具体处理者 :推送消息Handler
@Slf4j
public class JpushOrderHandler extends AbstractMessageHandler<OrderAction, Message> {
@Override
public OrderAction handleMessage(Message message) {
String tagList = BundleUtil.getResult("mq.tag");
String[] tags = tagList.split(",");
if (message.getTopic().equals(getTopic()) && Arrays.asList(tags).contains(message.getTag())) { //避免消费到其他消息 json转换报错
log.info(" 监听到推送消息,[topic:" + message.getTopic() + "], [tag:" + message.getTag() + "]。开始解析...");
try {
// res 是生产者传过来的消息内容
byte[] body = message.getBody();
String res = new String(body);
String substring = res.substring(res.length() -1, res.length());
PushInfo info = JSON.parseObject(res.substring(0, res.length() - 1), PushInfo.class);
if ("1".equals(substring)){
// 分组推送
CommonUtil.Jpush2SingleUserMq(info,true);
}else {
// 多个用户推送
CommonUtil.Jpush2SingleUserMq(info,false);
}
return OrderAction.Success;
}catch (Exception e) {
log.error("MessageListener.consume error:" + e.getMessage(), e);
return OrderAction.Suspend;
}
} else {
if (nextHandler == null) {
log.info("未匹配到topic:{}, tag:{}跳过,",message.getTopic(), message.getTag());
return OrderAction.Success;
}
return nextHandler.handleMessage(message);
}
}
}
具体处理者 :延时订单处理Handler
@Slf4j
public class DelayRemoveOrderHandler extends AbstractMessageHandler<OrderAction, Message> {
private static Lock lock = new ReentrantLock(true);
@Override
public OrderAction handleMessage(Message message) {
//消费延时订单tag
if (message.getTopic().equals(getTopic()) && message.getTag().equals(CommonConstants.TAG)) {
log.info(" 监听订单删除消息,[topic:" + message.getTopic() + "], [tag:" + message.getTag() + "]。开始解析...");
//userId + UNDER_BAR + borrowOrderId
try {
String content = new String(message.getBody(), Charsets.UTF_8);
log.info("消费内容 userId_borrowOrderId :{}", content);
if (StringUtils.isEmpty(content)) {
return OrderAction.Success;
}
String[] info = content.split(CommonConstants.UNDER_BAR);
String userId = info[0];
String key = CommonConstants.CART_ID_LIST + userId;
lock.tryLock(3, TimeUnit.SECONDS);
//查询用户购物车列表
String orders = RedisUtil.getString(key);
if (StringUtils.isEmpty(orders)) {
return OrderAction.Success;
}
List<Integer> orderList = JSONObject.parseArray(orders, Integer.class);
List<Integer> delList;
String idStr = info[1];
//判断是否是批量加入
if (idStr.startsWith(CommonConstants.LIST_MARK)) {
String[] s = content.split(CommonConstants.LIST_MARK);
delList = JSONObject.parseArray(s[1], Integer.class);
} else {
delList = Collections.singletonList(Integer.valueOf(info[1]));
}
orderList.removeAll(delList);
RedisUtil.setString(key, GsonUtil.objectConvertJson(orderList));
log.info("删除用户:{},延时订单:{},成功", userId, delList.toString());
return OrderAction.Success;
} catch (Exception e) {
//消费失败,挂起当前队列
log.error("延时订单:{}消费异常", new String(message.getBody(), Charsets.UTF_8));
return OrderAction.Suspend;
} finally {
lock.unlock();
}
} else {
if (nextHandler == null) {
log.info("未匹配到topic:{}, tag:{}跳过,",message.getTopic(), message.getTag());
return OrderAction.Success;
}
return nextHandler.handleMessage(message);
}
}
}
模式工厂 HandlerFactory
public final class HandlerFactory {
private static TypeConverterManager typeConverterManager = JoddBean.get().typeConverterManager();
public static <T, R>AbstractMessageHandler newJpushOrderHandler(){
return new JpushOrderHandler();
};
public static <T, R>AbstractMessageHandler newDelayRemoveOrderHandler(){
return new DelayRemoveOrderHandler();
}
/**
* 责任链模式
*/
@SafeVarargs
public static <T, R>AbstractMessageHandler<T, R> getHandlerResponsibilityChain(Class< ? extends AbstractMessageHandler<T, R>> ... handlers ) {
Preconditions.checkNotNull(handlers, "handler列表不能为空");
if (handlers.length == CommonConstants.TRUE) {
return BeanUtils.instantiate(handlers[CommonConstants.FIRST_ELEMENT]);
}
List<Object> list = Arrays.stream(handlers).map(BeanUtils::instantiate).collect(Collectors.toList());
AbstractMessageHandler<T, R> result = null;
for (int i = 1; i < list.size(); i++) {
AbstractMessageHandler<T, R> pre = typeConverterManager.convertType(list.get(i - 1), handlers[i - 1]);
AbstractMessageHandler<T, R> cur = typeConverterManager.convertType(list.get(i), handlers[i]);
cur.setNextHandler(pre);
result = cur;
}
return result;
}
}
getHandlerResponsibilityChain()
主要是创建责任链,动态生成自己想要的逻辑责任链
客户端调用
public class RoborderConsumerAdapter{
private OrderConsumer orderConsumer;
public RoborderConsumerAdapter(OrderConsumer orderConsumer) {
Assert.notNull(orderConsumer, "orderConsumer is null");
this.orderConsumer = orderConsumer;
}
/**
* 消费
*/
public void consumerMessages(){
AbstractCommonListener listener = BeanUtils.instantiate(GlobalOrderListener.class);
this.orderConsumer.subscribe(listener.getTopic(), "*", (MessageOrderListener) listener);
}
}
按这种设计方式,如果有一个新的业务处理场景,只需添加新的一个Handler实现抽象处理者就好,然后调用getHandlerResponsibilityChain()
的时候,加入想要使用的Handler,就能处理,这样不会导致多人维护代码时,出现逻辑混乱问题,业务直接解耦,减少开发和维护成本
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