我遇到以下情况：连接任意字符串和NULL值的Integer对象会导致NullPointerException：
Integer nullInt = null;
String someString = "abc";
System.out.println(someString + "=" + nullInt)
现在我希望结果会出现类似“abc = null”的内容，而Java会在连接之前尝试取消整理Integer对象。为什么会这样？
感谢您的帮助！
更新
所以这是原始代码，我在上面的例子中将其分解：
public class SomeClass {
private String id;
private String description;
private Integer someInteger;
private Date someDate;
private Date someOtherInteger;
// ...
public String toString(){
return "object [id=" + id
+ ", description=" + description
+ ", someInteger=" + someInteger
+ ", someDate=" + someDate
+ ", someOtherInteger=" + someOtherInteger;
}
// ...
}
“id”有一个值 “description”为空 “someInteger”有一个值 “someDate”为空 “someOtherInteger”为空
罪魁祸首是“someOtherInteger”，我可以在Eclipse调试器中重现错误，检查表达式“，someOtherInteger”+ someOtherInteger。 确切的Exception消息是：“intValue（）中的java.lang.NullPointerException”
有什么想法吗？
更新
这就是实际的代码，“lastMileage”是NULL ...
@Override
public String toString(){
return "OwnedCar [vin=" + vin
+ ", description=" + description
+ ", manufactureYear=" + manufactureYear
+ ", purchasedDate=" + purchasedDate
+ ", lastMileage=" + lastMileage
+ ", lastMileageDate=" + lastMileageDate
+ ", milesPerDay=" + milesPerDay
+ ", licencePlateNumber=" + licencePlateNumber
+ ", relationship=" + relationship
+ ", lifeCycleStage=" + lifeCycleStage
+ ", lastKnownDeliveryStatus=" + lastKnownDeliveryStatus
+ ", lastKnownDeliveryStatusChangeDate=" + lastKnownDeliveryStatusChangeDate
+ ", lastDeliveryStatusCheckDate=" + lastDeliveryStatusCheckDate
+ ", orderCanceledCode=" + orderCanceledCode
+ ", deactivatedIndicator=" + deactivatedIndicator
+ ", deactivationReason=" + deactivationReason
+ ", modelCode=" + modelCode
+ ", model=" + model
+ ", carAge=" + carAge
+ ", vinVerifiedDate=" + vinVerifiedDate
+ ", commissionNumber=" + commissionNumber
+ ", commissionNumberYear=" + commissionNumberYear
+ ", ownershipActivationCode=" + ownershipActivationCode
+ ", bid=" + bid
+ ", orderNumber=" + orderNumber
+ ", largePhotoUrl=" + largePhotoUrl
+ ", mediumPhotoUrl=" + mediumPhotoUrl
+ ", smallPhotoUrl=" + smallPhotoUrl
+ ", colourSalesFamily =( "+ colourSalesFamily != null ? colourSalesFamily.toString() : null + ")"
+ "]";
}
这是Stacktrace：
java.lang.NullPointerException
at ************.OwnedCar.toString(OwnedCar.java:671)
at java.lang.String.valueOf(String.java:2826)
at java.lang.StringBuilder.append(StringBuilder.java:115)
at com.vw.dbs.******.***SessionAttributeListener.attributeReplaced(***SessionAttributeListener.java:46)
at org.apache.catalina.session.StandardSession.setAttribute(StandardSession.java:1386)
at org.apache.catalina.session.StandardSession.setAttribute(StandardSession.java:1291)
at org.apache.catalina.session.StandardSessionFacade.setAttribute(StandardSessionFacade.java:130)
at com.liferay.util.servlet.SharedSessionWrapper.setAttribute(SharedSessionWrapper.java:145)
at com.liferay.portlet.PortletSessionImpl.setAttribute(PortletSessionImpl.java:273)
at com.liferay.portlet.PortletSessionImpl.setAttribute(PortletSessionImpl.java:260)
at org.springframework.web.portlet.context.PortletRequestAttributes.setAttribute(PortletRequestAttributes.java:156)
at org.springframework.web.bind.support.DefaultSessionAttributeStore.storeAttribute(DefaultSessionAttributeStore.java:54)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.updateModelAttributes(HandlerMethodInvoker.java:214)
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:363)
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter.doHandle(AnnotationMethodHandlerAdapter.java:347)
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter.handleRender(AnnotationMethodHandlerAdapter.java:289)
at org.springframework.web.portlet.DispatcherPortlet.doRenderService(DispatcherPortlet.java:734)
at org.springframework.web.portlet.FrameworkPortlet.processRequest(FrameworkPortlet.java:522)
at org.springframework.web.portlet.FrameworkPortlet.doDispatch(FrameworkPortlet.java:470)
at javax.portlet.GenericPortlet.render(GenericPortlet.java:233)
at com.liferay.portlet.FilterChainImpl.doFilter(FilterChainImpl.java:101)
at com.liferay.portal.kernel.portlet.PortletFilterUtil.doFilter(PortletFilterUtil.java:64)
at com.liferay.portal.kernel.servlet.PortletServlet.service(PortletServlet.java:92)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:551)
at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:488)
at com.liferay.portlet.InvokerPortletImpl.invoke(InvokerPortletImpl.java:638)
at com.liferay.portlet.InvokerPortletImpl.invokeRender(InvokerPortletImpl.java:723)
at com.liferay.portlet.InvokerPortletImpl.render(InvokerPortletImpl.java:425)
at org.apache.jsp.html.portal.render_005fportlet_jsp._jspService(render_005fportlet_jsp.java:1440)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:551)
at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:488)
at com.liferay.portal.util.PortalImpl.renderPortlet(PortalImpl.java:3715)
at com.liferay.portal.util.PortalUtil.renderPortlet(PortalUtil.java:1180)
at com.liferay.portlet.layoutconfiguration.util.RuntimePortletUtil.processPortlet(RuntimePortletUtil.java:160)
at com.liferay.portlet.layoutconfiguration.util.RuntimePortletUtil.processPortlet(RuntimePortletUtil.java:94)
at com.liferay.portlet.layoutconfiguration.util.RuntimePortletUtil.processTemplate(RuntimePortletUtil.java:256)
at com.liferay.portlet.layoutconfiguration.util.RuntimePortletUtil.processTemplate(RuntimePortletUtil.java:181)
at org.apache.jsp.html.portal.layout.view.portlet_jsp._jspService(portlet_jsp.java:821)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:551)
at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:488)
at com.liferay.portal.action.LayoutAction.includeLayoutContent(LayoutAction.java:361)
at com.liferay.portal.action.LayoutAction.processLayout(LayoutAction.java:618)
at com.liferay.portal.action.LayoutAction.execute(LayoutAction.java:229)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at com.liferay.portal.struts.PortalRequestProcessor.process(PortalRequestProcessor.java:152)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at com.liferay.portal.servlet.MainServlet.callParentService(MainServlet.java:518)
at com.liferay.portal.servlet.MainServlet.service(MainServlet.java:495)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.strip.StripFilter.processFilter(StripFilter.java:309)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.themepreview.ThemePreviewFilter.processFilter(ThemePreviewFilter.java:88)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.gzip.GZipFilter.processFilter(GZipFilter.java:137)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.secure.SecureFilter.processFilter(SecureFilter.java:182)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.autologin.AutoLoginFilter.processFilter(AutoLoginFilter.java:254)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at com.liferay.portal.servlet.FriendlyURLServlet.service(FriendlyURLServlet.java:133)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.strip.StripFilter.processFilter(StripFilter.java:261)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.themepreview.ThemePreviewFilter.processFilter(ThemePreviewFilter.java:88)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.gzip.GZipFilter.processFilter(GZipFilter.java:126)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.secure.SecureFilter.processFilter(SecureFilter.java:182)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.i18n.I18nFilter.processFilter(I18nFilter.java:211)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.autologin.AutoLoginFilter.processFilter(AutoLoginFilter.java:254)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at com.liferay.portal.servlet.I18nServlet.service(I18nServlet.java:101)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at com.liferay.portal.servlet.filters.virtualhost.VirtualHostFilter.processFilter(VirtualHostFilter.java:310)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:738)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.threadlocal.ThreadLocalFilter.processFilter(ThreadLocalFilter.java:35)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:470)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:555)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:190)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:291)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:774)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:703)
at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:896)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:690)
at java.lang.Thread.run(Thread.java:662)
答案 0 :(得分：5)
不是所以：
public static void main(String[] args) {
Integer nullInt = null;
String someString = "abc";
System.out.println(someString + "=" + nullInt);
}
输出：
abc=null
答案 1 :(得分：1)
我运行你的行，它写了abc=null。
答案 2 :(得分：1)
JLS 15.18.1.1（字符串与+操作数串联）：
如果引用为null，则将其转换为字符串“null”（四个 ASCII字符n，u，l，l）。否则，执行转换 好像是通过调用引用对象的toString方法 没有争论;但是如果调用toString方法的结果 为null，然后使用字符串“null”
以下代码
String a = "abc=" + anInteger;
永远不会抛出异常（尽管可能会写abc=null）
但如果你对它进行一些算术运算：
String a = "abc=" + (anInteger + 1)
如果取消装箱时anInteger为null，则显然会在rutime时抛出NPE。也许你没有发布你的整个代码
OP更新了他的答案，原因需要进一步解释
public class Main {
public static void main(String[] args) {
Integer i = null;
System.out.println("throw a NPE " + i != null ? i.toString() : null);
}
}
三元运算符周围没有括号，因此表达式计算为
System.out.println(("throw a NPE " + i) != null ? i.toString() : null);
首先应用字符串连接，因此“抛出NPE null”不是null而是调用i.toString()，抛出NPE