Camel异常策略匹配逻辑

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route 优先级大于 context

优先匹配 route 级别的异常策略， 然后匹配 context 级别的异常策略；

匹配逻辑

注意区分包装与继承

包装：ConnectException异常抛出后被包装成OrderFailedException异常，然后OrderFailedException异常又被包装成RuntimeCamelException异常，但是他们之间并不存在继承关系；

org.apache.camel.RuntimeCamelException (wrapper by Camel)
+ com.mycompany.OrderFailedException+ java.net.ConnectException

继承：而RuntimeCamelException继承RuntimeException异常，RuntimeException集成Exception异常

org.apache.camel.RuntimeCamelException
+ java.lang.RuntimeException+  java.lang.Exception

获取异常包装层级

以上述示例做参考，执行完该方法后，获取的异常列表为：

java.net.ConnectException
com.mycompany.OrderFailedException
org.apache.camel.RuntimeCamelException

public static Iterable<Throwable> createExceptionIterable(Throwable exception) {List<Throwable> throwables = new ArrayList<>();Throwable current = exception;// spool to the bottom of the caused by treewhile (current != null) {throwables.add(current);current = current.getCause();}// 此处有反转动作！！！Collections.reverse(throwables);return throwables;
}

遍历异常匹配处理策略

获取异常继承层级的递归算法：

private static int getInheritanceLevel(Class<?> clazz) {if (clazz == null || "java.lang.Object".equals(clazz.getName())) {return 0;}return 1 + getInheritanceLevel(clazz.getSuperclass());
}

判断异常与策略是否匹配的逻辑，以RuntimeCamelException异常匹配以下策略为例：

onException(Exception.class).maximumRedeliveries(1).redeliveryDelay(5000);

下述方法中，clazz 为 Exception.class, exception 为 RuntimeCamelException.class。

• 首先，判断RuntimeCamelException是否为Exception的实例；
• 然后，判断RuntimeCamelException与Exception是否为同一个类；
  • 如果是同一个类则为严格匹配；
  • 如果不为同一个类，则获取RuntimeCamelException与Exception之间的间隔层级
    • 如果间隔层级比现有的间隔层级小，则更新获选异常策略和异常层级信息

if (filter(type, clazz, exception)) {// must matchif (!matchesWhen(type, exchange)) {LOG.trace("The type did not match when: {}", type);continue;}// exact match then breakif (clazz.equals(exception.getClass())) {candidate = type;candidateDiff = 0;break;}// not an exact match so find the best candidateint level = getInheritanceLevel(clazz);int diff = targetLevel - level;if (diff < candidateDiff) {// replace with a much better candidatecandidate = type;candidateDiff = diff;}
}

获取最终的匹配策略

如果完全匹配则返回完全匹配的异常策略；
否则返回间隔层级小的异常策略；

代码

org.apache.camel.processor.errorhandler.DefaultExceptionPolicyStrategy#getExceptionPolicy

Test Code

@Test
public void testOnExceptionDirectMatch() throws Exception {context.addRoutes(new RouteBuilder() {@Overridepublic void configure() throws Exception {context.setTracing(true);onException(Exception.class).maximumRedeliveries(6);onException(OrderFailedException.class).maximumRedeliveries(3);from("direct:order").onException(Exception.class).maximumRedeliveries(10).end().bean(OrderServiceBean.class, "handleOrder");}});context.start();try {template.requestBody("direct:order", "ActiveMQ in Action");fail("Should throw an exception");Thread.sleep(10000l);} catch (CamelExecutionException e) {assertIsInstanceOf(OrderFailedException.class, e.getCause());}
}

在候选异常策略里包含两个异常策略，一个是完全匹配，来自global（camel context 级别），另外一个来自route（路由内配置）；最终会选择严格匹配的OrderFailedException匹配策略。

最终结果输出如下：

handler order!
handler order!
handler order!
handler order!

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