Spring Boot NullPointerException in InlibraryController.AddNum() - 解决方法 - 常规

2023-10-07 18:39:30.115 ERROR 20484 --- [io-8080-exec-10] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null at com.aaa.controller.InlibraryController.AddNum(InlibraryController.java:50) ~[classes/:na] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_221] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_221] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_221] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_221] 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:748) [na:1.8.0_221]

问题分析：

该错误日志表明在 com.aaa.controller.InlibraryController 类中的 AddNum() 方法（第 50 行）出现了 NullPointerException。这通常意味着代码在该行尝试访问一个空对象的属性或调用一个空对象的方法。

解决方案：

**检查 InlibraryController.java 文件第 50 行的代码：**仔细检查代码，确认代码试图访问的对象是否可能为空。可以使用条件语句或空值判断来避免对空对象的访问。
**检查 AddNum() 方法的输入参数：**确保在调用 AddNum() 方法时传入的参数不为空。检查输入参数的来源，并确保它们在调用方法之前已被正确赋值。

示例：

// InlibraryController.java 文件中的 AddNum() 方法
public String AddNum(Integer num) {
    // 检查输入参数是否为空
    if (num == null) {
        // 处理空参数的情况
        return "参数为空";
    }

    // 访问可能为空的对象
    SomeObject obj = getSomeObject(); // 获取可能为空的对象
    if (obj != null) {
        // 访问对象的属性或方法
        return obj.getProperty() + num;
    } else {
        // 处理对象为空的情况
        return "对象为空";
    }
}

总结：

空指针异常通常是由于代码中对空对象进行了操作或调用造成的。通过仔细检查代码，并使用条件语句或空值判断来避免对空对象的访问，可以有效解决这类问题。

Spring Boot NullPointerException in InlibraryController.AddNum() - 解决方法