如何在预先编译的jar文件的nullpointerexception处停止执行之前进行调试？

Question

我想调试为什么一个对象从这一行返回null

debug_log = LoggingConfigFileLoader.getLogFilePaths().get("debug.log");

在这里：https://github.com/UniversalMediaServer/UniversalMediaServer/blob/master/src/main/java/net/pms/PMS.java#L356

我希望知道在异常发生之前发生了什么java执行。不幸的是，.jar来自一个大项目，可能很难构建。尤其是对我来说，谁都不懂java。这是在openjdk7上的，( java开发人员也使用它)。但是，代码以前从未在FreeBSD上运行过。

最后，我想找出这个未处理异常的真正原因/根本原因：

ums4 UMS/ root~# /usr/local/openjdk7/bin/java -Djava.awt.headless=true -classpath /usr/local/share/universal-media-server/ums.jar net.pms.PMS
 18:18:12.424 [main] DEBUG o.a.c.c.ConfigurationUtils - ConfigurationUtils.locate(): base is null, name is /root/.config/UMS/UMS.conf
 18:18:12.430 [main] DEBUG o.a.c.c.DefaultFileSystem - Could not locate file /root/.config/UMS/UMS.conf at null: no protocol: /root/.config/UMS/UMS.conf
 18:18:12.431 [main] DEBUG o.a.c.c.ConfigurationUtils - Loading configuration from the absolute path /root/.config/UMS/UMS.conf
 18:18:12.431 [main] DEBUG o.a.c.c.PropertiesConfiguration - Base path set to file:///root/.config/UMS/UMS.conf
 18:18:12.463 [main] DEBUG o.a.c.c.PropertiesConfiguration - FileName set to UMS.conf
 18:18:12.464 [main] DEBUG o.a.c.c.PropertiesConfiguration - Base path set to /root/.config/UMS
 18:18:12.480 [main] DEBUG n.p.c.ConfigurationReader - Reading cred.path: default: "", current: "/root/.config/UMS/UMS.cred"
 18:18:12.498 [main] INFO  net.pms.PMS - Starting Universal Media Server 4.0.0-a1
 18:18:12.499 [main] INFO  net.pms.PMS - Based on PS3 Media Server by shagrath, copyright 2008-2014
 18:18:12.499 [main] INFO  net.pms.PMS - http://www.universalmediaserver.com
 18:18:12.499 [main] INFO  net.pms.PMS - 
 18:18:12.499 [main] INFO  net.pms.PMS - Build: 38318285b (2014-06-02)
 18:18:12.499 [main] INFO  net.pms.PMS - Java: OpenJDK 64-Bit Server VM 1.7.0_60 64-bit by Oracle Corporation
 18:18:12.500 [main] INFO  net.pms.PMS - OS: FreeBSD 64-bit 9.2-RELEASE-p3
 18:18:12.500 [main] INFO  net.pms.PMS - Encoding: US-ASCII
 18:18:12.522 [main] INFO  net.pms.PMS - Memory: 313 MB
 18:18:12.522 [main] INFO  net.pms.PMS - Language: en
 18:18:12.522 [main] INFO  net.pms.PMS - 
 18:18:12.523 [main] INFO  net.pms.PMS - Working directory: /var/db/universal-media-server/.config/UMS
 18:18:12.525 [main] INFO  net.pms.PMS - Temp directory: /tmp/universalmediaserver
 18:18:12.525 [main] INFO  net.pms.PMS - Logging config file: internal defaults
 18:18:12.526 [main] INFO  net.pms.PMS - 
 18:18:12.526 [main] INFO  net.pms.PMS - Profile directory: /root/.config/UMS
 18:18:12.527 [main] INFO  net.pms.PMS - Profile directory permissions: rw
 18:18:12.527 [main] INFO  net.pms.PMS - Profile path: /root/.config/UMS/UMS.conf
 18:18:12.527 [main] INFO  net.pms.PMS - Profile permissions: rw
 18:18:12.527 [main] INFO  net.pms.PMS - Profile name: ums4
 18:18:12.528 [main] INFO  net.pms.PMS - 
 18:18:12.528 [main] INFO  net.pms.PMS - Web conf path: /root/.config/UMS/WEB.conf
 18:18:12.528 [main] INFO  net.pms.PMS - Web conf permissions: file not found
 18:18:12.528 [main] INFO  net.pms.PMS - 
 18:18:12.540 [main] ERROR net.pms.PMS - A serious error occurred during PMS init
 java.lang.NullPointerException: null
    at net.pms.newgui.DbgPacker.<init>(DbgPacker.java:40) ~[ums.jar:4.0.0-a1]
    at net.pms.PMS.displayBanner(PMS.java:357) [ums.jar:4.0.0-a1]
    at net.pms.PMS.init(PMS.java:509) [ums.jar:4.0.0-a1]
    at net.pms.PMS.createInstance(PMS.java:1038) [ums.jar:4.0.0-a1]
    at net.pms.PMS.main(PMS.java:1138) [ums.jar:4.0.0-a1]

Answer 1

您可以尝试将项目加载到IDE中，并设置“中断异常”断点(例如，在Eclipse中，它位于"Run -> Add Java断点.“中)。

但我相信这种方法只适用于较小的工程。例如，昨天我厌倦了等待，而番石榴的先决条件检查中断了长批处理的执行，我添加了一些日志并重新运行进程w/o调试器。所以YMMV。