Java NullPointerException: 解决方案和示例

java.lang.NullPointerException: null at com.scq.Controller.PepoleController.lambda$edit$1(PepoleController.java:73) ~[classes/:na] at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174) ~[na:1.8.0_382] at java.util.ArrayList$ArrayListSpliterator.tryAdvance(ArrayList.java:1361) ~[na:1.8.0_382] at java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:126) ~[na:1.8.0_382] at java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:499) ~[na:1.8.0_382] at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:486) ~[na:1.8.0_382] at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472) ~[na:1.8.0_382] at java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:152) ~[na:1.8.0_382] at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:1.8.0_382] at java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:531) ~[na:1.8.0_382] at com.scq.Controller.PepoleController.edit(PepoleController.java:73) ~[classes/:na] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_382] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_382] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_382] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_382] at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.30.jar:5.3.30] at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.30.jar:5.3.30] at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.30.jar:5.3.30] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.30.jar:5.3.30] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.30.jar:5.3.30] at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.30.jar:5.3.30] at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1072) ~[spring-webmvc-5.3.30.jar:5.3.30] at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:965) ~[spring-webmvc-5.3.30.jar:5.3.30] at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.30.jar:5.3.30] at org.springframework.web.servlet.FrameworkServlet.doPut(FrameworkServlet.java:920) ~[spring-webmvc-5.3.30.jar:5.3.30] at javax.servlet.http.HttpServlet.service(HttpServlet.java:558) ~[tomcat-embed-core-9.0.80.jar:4.0.FR] at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.30.jar:5.3.30] at javax.servlet.http.HttpServlet.service(HttpServlet.java:623) ~[tomcat-embed-core-9.0.80.jar:4.0.FR] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:209) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-9.0.80.jar:9.0.80] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.30.jar:5.3.30] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.30.jar:5.3.30] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.30.jar:5.3.30] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.30.jar:5.3.30] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.30.jar:5.3.30] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.30.jar:5.3.30] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:168) ~[tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:481) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:130) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:390) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:926) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1790) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) [tomcat-embed-core-9.0.80.jar:9.0.80] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.80.jar:9.0.80] at java.lang.Thread.run(Thread.java:750) [na:1.8.0_382]

这个异常信息表明在 com.scq.Controller.PepoleController.java 文件的第 73 行，一个 lambda 表达式试图访问一个 null 对象。

可能的解决方案:

检查代码: 仔细检查 PepoleController.java 文件的第 73 行，确定哪个变量可能为 null。
添加 null 检查: 在访问变量之前，使用 if 语句或 Optional 类检查该变量是否为 null。
调试: 使用调试器来跟踪代码执行流程，找出哪个变量在 lambda 表达式中被设置为 null。

最佳实践:

在访问对象之前始终检查其是否为 null。
避免使用可变变量，尤其是全局变量。
使用 Optional 类来表示可能为 null 的值。
使用静态代码分析工具来检测潜在的 NullPointerException 错误。

示例:

// 原始代码，可能出现 NullPointerException
String name = null;
System.out.println(name.length());

// 添加 null 检查
if (name != null) {
    System.out.println(name.length());
} else {
    System.out.println('Name is null.');
}

// 使用 Optional 类
Optional<String> nameOptional = Optional.ofNullable(name);
nameOptional.ifPresent(n -> System.out.println(n.length()));

通过仔细检查代码、添加 null 检查和使用最佳实践，你可以有效地避免 NullPointerException 错误并提高代码的健壮性。