我是数据统计图出不来了，不知道哪里错了

Question

有一个统计近七天发布文章的数量，但是报错了，没有数据。
报错如下：

2024-05-22 15:26:21.213 ERROR 25416 --- [nio-9090-exec-9] c.e.exception.GlobalExceptionHandler     : 异常信息：

java.lang.NullPointerException: null
    at com.example.service.NotebookService.lambda$selectCount$0(NotebookService.java:154) ~[classes/:na]
    at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174) ~[na:1.8.0_351]
    at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1384) ~[na:1.8.0_351]
    at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482) ~[na:1.8.0_351]
    at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472) ~[na:1.8.0_351]
    at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[na:1.8.0_351]
    at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:1.8.0_351]
    at java.util.stream.LongPipeline.reduce(LongPipeline.java:439) ~[na:1.8.0_351]
    at java.util.stream.LongPipeline.sum(LongPipeline.java:397) ~[na:1.8.0_351]
    at java.util.stream.ReferencePipeline.count(ReferencePipeline.java:526) ~[na:1.8.0_351]
    at com.example.service.NotebookService.selectCount(NotebookService.java:154) ~[classes/:na]
    at com.example.controller.NotebookController.selectCount(NotebookController.java:105) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_351]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_351]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_351]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_351]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.15.jar:5.3.15]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.15.jar:5.3.15]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.15.jar:5.3.15]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.15.jar:5.3.15]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.15.jar:5.3.15]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.15.jar:5.3.15]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1067) ~[spring-webmvc-5.3.15.jar:5.3.15]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) ~[spring-webmvc-5.3.15.jar:5.3.15]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) [spring-webmvc-5.3.15.jar:5.3.15]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) [spring-webmvc-5.3.15.jar:5.3.15]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:655) [tomcat-embed-core-9.0.56.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) [spring-webmvc-5.3.15.jar:5.3.15]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:764) [tomcat-embed-core-9.0.56.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) [tomcat-embed-websocket-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:91) [spring-web-5.3.15.jar:5.3.15]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) [spring-web-5.3.15.jar:5.3.15]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) [spring-web-5.3.15.jar:5.3.15]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) [spring-web-5.3.15.jar:5.3.15]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) [spring-web-5.3.15.jar:5.3.15]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) [spring-web-5.3.15.jar:5.3.15]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) [spring-web-5.3.15.jar:5.3.15]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) [spring-web-5.3.15.jar:5.3.15]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:540) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:895) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1732) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.56.jar:9.0.56]
    at java.lang.Thread.run(Thread.java:750) [na:1.8.0_351

我的业务代码如下：

 public List<Dict> selectCount() {
        List<Notebook> notebookList = notebookMapper.selectAll(null);  // 查出所有的美食菜谱
        // 先查最近一周的日期
        Date today = new Date();
        DateTime yesterday = DateUtil.offsetDay(today, -1);
        DateTime date = DateUtil.offsetDay(today, -7);
        List<DateTime> dateTimeList = DateUtil.rangeToList(date, yesterday, DateField.DAY_OF_YEAR);
        List<String> dateList = dateTimeList.stream().map(DateUtil::formatDate).collect(Collectors.toList());
        List<Dict> dictList = new ArrayList<>();
        for (String dateStr : dateList) {
            long count = notebookList.stream().filter(foods -> foods.getDate().contains(dateStr)).count();
            Dict dict = Dict.create().set("date", dateStr.substring(5)).set("count", count);
            dictList.add(dict);
        }
        return dictList;
    }

Answer 1

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根据提供的错误信息和代码片段，看起来你在尝试获取近七天发布的文章数量时遇到了NullPointerException。这个异常通常发生在你试图访问一个为null的对象的方法或属性。在你的代码中，错误可能源于notebookList为空，即notebookMapper.selectAll(null)返回了null或者空列表。

要解决这个问题，你需要确保从数据库查询到的数据不为空。首先检查一下你的数据库连接是否正常，以及查询方法selectAll()是否正确执行并返回预期的数据。如果selectAll()返回的是null，那么可能是由于一些原因（例如：配置错误、数据库连接失败等）导致查询失败。如果它返回的是空列表，那可能是因为在过去的七天内确实没有发布任何文章。

为了修复这个问题，可以添加一些日志记录来确认上述猜测，并且处理可能的null值。以下是修改后的代码，包括日志记录和对null值的处理：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

// ...

private static final Logger logger = LoggerFactory.getLogger(NotebookService.class);

public List<Dict> selectCount() {
    List<Notebook> notebookList = notebookMapper.selectAll(null);  // 查出所有的美食菜谱

    if (notebookList == null) {
        logger.error("selectAll() returned null. Check database connection and query.");
        return Collections.emptyList();  // 返回空列表，避免进一步的NPE
    }

    if (notebookList.isEmpty()) {
        logger.info("selectAll() returned an empty list. No articles were published in the last seven days.");
        return Collections.emptyList();  // 如果无数据，也返回空列表
    }

    // ... 剩下的代码保持不变 ...
}

此外，确保你的Notebook类中的getDate()方法不会返回null。如果可能的话，在数据库查询时就排除掉日期为空的文章，这样能减少后续处理的复杂性。

如果你的问题仍然存在，请检查你的notebookMapper.selectAll()实现，确保它正确地连接到数据库并执行SQL查询。如果问题依然存在，你可能需要提供更多的上下文，比如notebookMapper的定义和它的实现细节，或者数据库表结构和示例数据，以便进行更深入的分析。