java - 当 catch 并没有真正捕捉到任何东西时

Question

这个问题在这里已经有了答案:

"Comparison method violates its general contract!" (13 个回答)

关闭 4年前.

由于最近存储在数据库中的错误数据，我遇到了程序崩溃。这让我很困惑，因为我认为我有办法防止这种情况发生。

以下代码的目的是比较员工徽章编号并对其进行排序。如果有错误，返回 -1 并继续前进——不要因为几千个徽章编号中的一个错误而停止:

public int compare(Employee t, Employee t1) {
    Integer returnValue = -1;
    try {
        Integer tb = Integer.parseInt(t.getBadgeNumber());
        Integer t1b = Integer.parseInt(t1.getBadgeNumber());
        returnValue = tb.compareTo(t1b);
    } catch (Exception e) {
        returnValue = -1;//useless statement, I know.
    }
    return returnValue;
}

当错误的徽章编号命中时(在本例中为 t)，我得到一个“java.lang.IllegalArgumentException:比较方法违反其一般契约(Contract)!”错误而不是在 catch 中返回 -1。

我对这里的捕获有什么不明白的地方？

完整的堆栈跟踪:

16-May-2018 14:28:53.496 SEVERE [http-nio-8084-exec-601] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [RequestServlet] in context with path [/AppearanceRequest] threw exception
 java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.TimSort.mergeHi(TimSort.java:868)
at java.util.TimSort.mergeAt(TimSort.java:485)
at java.util.TimSort.mergeForceCollapse(TimSort.java:426)
at java.util.TimSort.sort(TimSort.java:223)
at java.util.TimSort.sort(TimSort.java:173)
at java.util.Arrays.sort(Arrays.java:659)
at java.util.Collections.sort(Collections.java:217)
at org.bcso.com.appearancerequest.html.NotifierHTML.getHTML(NotifierHTML.java:363)
at org.bcso.com.appearancerequest.AppearanceRequestServlet.processRequest(AppearanceRequestServlet.java:96)
at org.bcso.com.appearancerequest.AppearanceRequestServlet.doGet(AppearanceRequestServlet.java:565)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:618)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:301)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:136)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:74)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:516)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1015)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:652)
at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1575)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1533)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)

调用代码:

    List<Employee> employeeList = DatabaseUtil.getEmployees();
    Collections.sort(employeeList, new BadgeComparator());

Answer 1

异常(无论它是什么)被 catch (Exception e) 捕获.你没有记录这个异常，所以你不知道它是什么。你应该以某种方式记录它，这样你就知道到底发生了什么。

返回 -1 时出现问题.这允许不一致的排序的可能性，Java 的当前排序算法有时会遇到这种情况。简而言之，返回 -1出现错误意味着您断言 a < b和 b < a是真的，因为在这两种情况下都会捕获异常。这在逻辑上是不正确的。排序算法检测到这一点并抛出 IllegalArgumentException .请注意 compare方法在您的堆栈跟踪中 not ；这是对 Collections.sort 的调用.

除了记录异常之外，在您进入程序中的比较步骤之前对其进行处理。如果您必须将字符串解析为整数，请在创建 Employee 时执行此操作。对象，以便在您进入程序中的排序步骤之前进行验证。一个 Comparator不必验证数据；它应该只比较数据。