PDF小丑突出顯示多個搜索詞失敗，因為PDF包含圖像，彩色文本，復雜圖

Question

我正在使用PDFClown突出顯示PDF文檔中的多個搜索詞。 在許多包含彩色圖像，復雜圖的pdf文檔中，彩色文本PDFClown在那里引發異常，並且不能突出顯示匹配的單詞。 提到的代碼對於普通或簡單的Pdf都可以正常工作。

這是我用來測試https://drive.google.com/file/d/0B-nuOO6Zsa4rXy1DS2JjX1RnYmM/view?usp=sharing的PDF

    public void searchWordInPdf(DocumentMetadata documentMetadata , String searchWord,
                                HttpServletResponse response)throws IOException{
        try {
            byte[] bytes = null;
            org.pdfclown.files.File file =null;
            if (documentMetadata.getProject().getFtpId() != null && documentMetadata.getProject().getFtpId() > 0) {
                FtpServer ftpServer = ftpServerService.getFtpServer(documentMetadata.getProject().getFtpId());

                ByteArrayOutputStream bos = new ByteArrayOutputStream();
                retrievePdfFile(ftpServer, bos, documentMetadata.getFilePath());
                bytes = bos.toByteArray();
                 file = new org.pdfclown.files.File(bytes);
            }else{
                 file = new org.pdfclown.files.File(documentMetadata.getFilePath());
            }
            List<String> matchList = new ArrayList<String>();
            //Pattern regex = Pattern.compile("[^\\s\"']+|\"([^\"]*)\"|'([^']*)'");
            Pattern regex = Pattern.compile("[^\\s\"']+|\"([^\"]*)\"|'([^']*)'");
            Matcher regexMatcher = regex.matcher(searchWord);
            while (regexMatcher.find()) {
                if (regexMatcher.group(1) != null) {
                    // Add double-quoted string without the quotes
                    matchList.add(regexMatcher.group(1));
                } else if (regexMatcher.group(2) != null) {
                    // Add single-quoted string without the quotes
                    matchList.add(regexMatcher.group(2));
                } else {
                    // Add unquoted word
                    matchList.add(regexMatcher.group());
                }
            }

            for (String key : matchList){
            Pattern pattern = Pattern.compile(key, Pattern.CASE_INSENSITIVE);
            // 2. Iterating through the document pages...
            TextExtractor textExtractor = new TextExtractor(true, true);
            for (final Page page : file.getDocument().getPages()) {
                System.out.println("\nScanning page " + (page.getIndex() + 1) + "...\n");

                // 2.1. Extract the page text!
                Map<Rectangle2D, List<ITextString>> textStrings = textExtractor.extract(page);
                // 2.2. Find the text pattern matches!
                final Matcher matcher = pattern.matcher(TextExtractor.toString(textStrings));

                // 2.3. Highlight the text pattern matches!
                textExtractor.filter(
                    textStrings,
                    new TextExtractor.IIntervalFilter() {
                        @Override
                        public boolean hasNext() {
                            if (matcher.find()) {
                                //count++;
                                return true;
                            }
                            return false;
                        }

                        @Override
                        public Interval<Integer> next() {
                            return new Interval<Integer>(matcher.start(), matcher.end());
                        }

                        @Override
                        public void process(
                            Interval<Integer> interval,
                            ITextString match
                        ) {
                            Rectangle2D textBox = null;
                            // Defining the highlight box of the text pattern match...
                            List<Quad> highlightQuads = new ArrayList<Quad>();
                            {
                        /*
                            NOTE: A text pattern match may be split across multiple contiguous lines,
                             so we have to define a distinct highlight box for each text chunk.
                        */

                                for (TextChar textChar : match.getTextChars()) {
                                    Rectangle2D textCharBox = textChar.getBox();
                                    if (textBox == null) {
                                        textBox = (Rectangle2D) textCharBox.clone();
                                    } else {
                                        if (textCharBox.getY() > textBox.getMaxY()) {
                                            highlightQuads.add(Quad.get(textBox));
                                            textBox = (Rectangle2D) textCharBox.clone();
                                        } else {
                                            textBox.add(textCharBox);
                                        }
                                    }
                                }
                                highlightQuads.add(Quad.get(textBox));
                            }
                            // Highlight the text pattern match!
                            new TextMarkup(page, highlightQuads, null, MarkupTypeEnum.Highlight);
                        }

                        @Override
                        public void remove() {
                            throw new UnsupportedOperationException();
                        }
                    }
                );
            }
        }
                String contentType = getContentType(documentMetadata.getFileName());
                if (contentType == null) {
                    contentType = "binary/octet-stream";
                }
            response.setStatus(HttpStatus.OK.value());
            ByteArrayOutputStream output = new ByteArrayOutputStream();
            if(output != null){
                file.save(output, SerializationModeEnum.Standard );
                bytes =  org.springframework.security.crypto.codec.Base64.encode(output.toByteArray());
                response.addHeader("Content-Disposition", "attachment; filename=" + documentMetadata.getFileName());
                response.addHeader("Content-Type", contentType);
                response.getOutputStream().write(bytes);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

這是StackTrace

 java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.TimSort.mergeLo(TimSort.java:777)
at java.util.TimSort.mergeAt(TimSort.java:514)
at java.util.TimSort.mergeCollapse(TimSort.java:439)
at java.util.TimSort.sort(TimSort.java:245)
at java.util.Arrays.sort(Arrays.java:1512)
at java.util.ArrayList.sort(ArrayList.java:1454)
at java.util.Collections.sort(Collections.java:175)
at org.pdfclown.tools.TextExtractor.sort(TextExtractor.java:675)
at org.pdfclown.tools.TextExtractor.extract(TextExtractor.java:306)
at nu.optimise.projectweb.service.DocumentMetadataService.searchWordInPdf(DocumentMetadataService.java:2669)
at nu.optimise.projectweb.service.DocumentMetadataService$$FastClassBySpringCGLIB$$fc6434c2.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:720)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:85)
at nu.optimise.projectweb.aop.logging.LoggingAspect.logAround(LoggingAspect.java:51)
at sun.reflect.GeneratedMethodAccessor186.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:620)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:609)
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:68)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.aspectj.AspectJAfterThrowingAdvice.invoke(AspectJAfterThrowingAdvice.java:59)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:281)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:655)
at nu.optimise.projectweb.service.DocumentMetadataService$$EnhancerBySpringCGLIB$$c3a15a18.searchWordInPdf(<generated>)
at nu.optimise.projectweb.web.rest.DocumentMetadataResource.searchContentPDF(DocumentMetadataResource.java:1026)
at nu.optimise.projectweb.web.rest.DocumentMetadataResource$$FastClassBySpringCGLIB$$bb12eea8.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:720)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:85)
at nu.optimise.projectweb.aop.logging.LoggingAspect.logAround(LoggingAspect.java:51)
at sun.reflect.GeneratedMethodAccessor186.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:620)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:609)
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:68)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.aspectj.AspectJAfterThrowingAdvice.invoke(AspectJAfterThrowingAdvice.java:59)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at com.ryantenney.metrics.spring.TimedMethodInterceptor.invoke(TimedMethodInterceptor.java:48)
at com.ryantenney.metrics.spring.TimedMethodInterceptor.invoke(TimedMethodInterceptor.java:34)
at com.ryantenney.metrics.spring.AbstractMetricMethodInterceptor.invoke(AbstractMetricMethodInterceptor.java:59)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:655)
at nu.optimise.projectweb.web.rest.DocumentMetadataResource$$EnhancerBySpringCGLIB$$bfe48b3d.searchContentPDF(<generated>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:832)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:743)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:961)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:895)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:858)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at com.codahale.metrics.servlet.AbstractInstrumentedFilter.doFilter(AbstractInstrumentedFilter.java:104)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.boot.actuate.autoconfigure.EndpointWebMvcAutoConfiguration$ApplicationContextHeaderFilter.doFilterInternal(EndpointWebMvcAutoConfiguration.java:281)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:115)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:317)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:115)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:112)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:169)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at nu.optimise.projectweb.security.jwt.JWTFilter.doFilter(JWTFilter.java:43)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:121)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:66)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:106)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:214)
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:177)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:87)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1099)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:670)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)

Answer 1

這是PDF Clown中的一個錯誤：在文本提取過程中，它使用自定義的Comparator實現，該實現未完全遵循Comparator合同。 在Java 7及以下版本中，此內容被忽略，但在Java 8中，這導致了手頭的異常。 如果您指示Java使用舊的排序算法，則程序將毫無例外地運行。

比較器

這是錯誤的比較器

  /**
    Text string position comparator.
   */
  private static class TextStringPositionComparator
    implements Comparator<ITextString>
  {
    /**
      Gets whether the specified boxes lay on the same text line.
    */
    public static boolean isOnTheSameLine(
      Rectangle2D box1,
      Rectangle2D box2
      )
    {
      /*
        NOTE: In order to consider the two boxes being on the same line,
        we apply a simple rule of thumb: at least 25% of a box's height MUST
        lay on the horizontal projection of the other one.
      */
      double minHeight = Math.min(box1.getHeight(), box2.getHeight());
      double yThreshold = minHeight * .75;
      return ((box1.getY() > box2.getY() - yThreshold
          && box1.getY() < box2.getMaxY() + yThreshold - minHeight)
        || (box2.getY() > box1.getY() - yThreshold
          && box2.getY() < box1.getMaxY() + yThreshold - minHeight));
    }

    @Override
    public int compare(
      ITextString textString1,
      ITextString textString2
      )
    {
      Rectangle2D box1 = textString1.getBox();
      Rectangle2D box2 = textString2.getBox();
      if(isOnTheSameLine(box1,box2))
      {
        /*
          [FIX:55:0.1.3] In order not to violate the transitive condition, equivalence on x-axis
          MUST fall back on y-axis comparison.
        */
        int xCompare = Double.compare(box1.getX(), box2.getX());
        if(xCompare != 0)
          return xCompare;
      }
      return Double.compare(box1.getY(), box2.getY());
    }
  }

如注釋[FIX:55:0.1.3] ... ，作者已經遇到排序問題。 不過，不幸的是，他只解決了一個麻煩的情況。

顯然， isOnTheSameLine compare使用的isOnTheSameLine測試通常可能是非傳遞性的原因，請考慮具有三個ITextString實例A ， B和C ：

（這可能會在常規文本中發生，例如，在一行中先有一些下標文本，然后是一些普通文字，然后是上標。）

A和B以及B和C在同一條直線上，但A和C則不在同一條直線上。 因此，前兩對將分別通過x坐標進行比較，而最后一對將通過y坐標進行比較，從而導致非傳遞性：

• A <B和
• B <C，但是
• A> C（PDF小丑使用y坐標向下增加）。

考慮兩個ITextString實例A和B的情況，也可能會違反身份條件，這兩個實例都具有相同的框，即都具有相同的尺寸並被打印在相同的位置（例如，從重疊的字母中構建符號）。 compare將返回0 ，只有在將一個對象與它的相等對象進行比較時才應該發生（“應該”，因為這只是建議，並非嚴格要求）。

不過，最常見的是，比較器會按照人們認為正確的方式對文本片段進行排序。

解決方法

在Java 8之前，內置的Java排序算法尚未測試Comparator實現是否滿足合同。 排序結果可能未正確排序，但排序未引發任何異常。 （不過，某些后來調用的例程假定要排序的數組可能會失敗得很小。）

但是，Java 8使用不同的默認排序算法，該算法進行一些完整性檢查，以識別未履行的Comparator合同對排序過程的影響。

但是通過使用命令行JRE參數

-Djava.util.Arrays.useLegacyMergeSort=true

您可以告訴Java 8使用不會​​因異常而失敗的舊排序方法。