Java FileInputStream NullpointerException
我正在尝试读取属性文件Java FileInputStream NullpointerException,java,java-io,Java,Java Io,我正在尝试读取属性文件/res/version.num。 但我得到的只是一个NPE try { URL url = getClass().getResource("/res/version.num"); logger.writeLog(JammEnum.INFO, "version.num path: " + url.getPath()); File prop_file = new File(url.getPath()); FileInputStream fis
/res/version.num
。
但我得到的只是一个NPE
try {
URL url = getClass().getResource("/res/version.num");
logger.writeLog(JammEnum.INFO, "version.num path: " + url.getPath());
File prop_file = new File(url.getPath());
FileInputStream fis = new FileInputStream(prop_file);
prop.load(fis);
fis.close();
}
catch (FileNotFoundException e) {
logger.writeLog(JammEnum.ERROR, "File not found: version.num");
e.printStackTrace();
}
catch (IOException e) {
logger.writeLog(JammEnum.ERROR, "Cannot read version.num");
e.printStackTrace();
}
输出为:
(II) - version.num path: /home/andreas/Programmieren/Java/Jamm/bin/res/version.num
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at jamm.gui.InfoGui.<init>(InfoGui.java:83)
at jamm.gui.FinanzmanagerGui$ButtonInfoListener.actionPerformed(FinanzmanagerGui.java:553)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6504)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6269)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4860)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4686)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2713)
at java.awt.Component.dispatchEvent(Component.java:4686)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:680)
at java.awt.EventQueue$4.run(EventQueue.java:678)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:677)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
(II)-version.num路径:/home/andreas/Programmieren/Java/Jamm/bin/res/version.num
线程“AWT-EventQueue-0”java.lang.NullPointerException中出现异常
位于jamm.gui.InfoGui(InfoGui.java:83)
在jamm.gui.FinanzmanagerGui$ButtonInfoListener.actionPerformed处(FinanzmanagerGui.java:553)
在javax.swing.AbstractButton.fireActionPerformed上(AbstractButton.java:2018)
位于javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
在javax.swing.DefaultButtonModel.fireActionPerformed上(DefaultButtonModel.java:402)
在javax.swing.DefaultButtonModel.setPressed中(DefaultButtonModel.java:259)
在javax.swing.plaf.basic.BasicButtonListener.MouseRelease(BasicButtonListener.java:252)
位于java.awt.Component.ProcessMouseeEvent(Component.java:6504)
位于javax.swing.JComponent.ProcessMouseeEvent(JComponent.java:3321)
位于java.awt.Component.processEvent(Component.java:6269)
位于java.awt.Container.processEvent(Container.java:2229)
位于java.awt.Component.dispatchEventImpl(Component.java:4860)
位于java.awt.Container.dispatchEventImpl(Container.java:2287)
位于java.awt.Component.dispatchEvent(Component.java:4686)
位于java.awt.LightweightDispatcher.RetargetMouseeEvent(Container.java:4832)
位于java.awt.LightweightDispatcher.ProcessMouseeEvent(Container.java:4492)
位于java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
位于java.awt.Container.dispatchEventImpl(Container.java:2273)
位于java.awt.Window.dispatchEventImpl(Window.java:2713)
位于java.awt.Component.dispatchEvent(Component.java:4686)
位于java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707)
在java.awt.EventQueue.access$000(EventQueue.java:101)
在java.awt.EventQueue$3.run(EventQueue.java:666)
在java.awt.EventQueue$3.run(EventQueue.java:664)
位于java.security.AccessController.doPrivileged(本机方法)
位于java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
位于java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
在java.awt.EventQueue$4.run(EventQueue.java:680)
在java.awt.EventQueue$4.run(EventQueue.java:678)
位于java.security.AccessController.doPrivileged(本机方法)
位于java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
位于java.awt.EventQueue.dispatchEvent(EventQueue.java:677)
位于java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
位于java.awt.EventDispatchThread.PumpeEventsforFilter(EventDispatchThread.java:128)
位于java.awt.EventDispatchThread.PumpeEventsforHierarchy(EventDispatchThread.java:117)
位于java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
位于java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
在java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
第83行是:FileInputStream fis=新的FileInputStream(prop_文件)
文件的路径记录正确。但为什么会出现此异常?您需要使用,而不是FileInputStream。试试这个例子
$ cat src/PrintVersion.java
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
/**
* @author peter.lawrey
*/
public class PrintVersion {
public static void main(String... args) throws IOException {
InputStream is = PrintVersion.class.getClassLoader().getResourceAsStream("res/version.num");
String version = asString(is);
System.out.println("Version: "+version);
}
public static String asString(InputStream is) throws IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] bytes = new byte[1024];
for(int len; (len = is.read(bytes))>0;)
baos.write(bytes, 0, len);
return baos.toString();
}
}
$ cat src/res/version.num
version 1.0
$ javac src/PrintVersion.java
$ ls src
PrintVersion.class PrintVersion.java res
$ java -cp src PrintVersion
Version: version 1.0
url
为空,因为它找不到资源。即使它不为null,这也不是获取文件的正确方法,因为只有当文件位于文件系统上时,它才会工作
你应该试试
InputStream is = getClass().getClassLoader()
.getResourceAsInputStream("/res/version.num");
谢谢你的帮助。但我仍然得到这个NPE。这条路对吗?对于所有这些问题,我很抱歉,我对编码很陌生。目前我的文件位于“Project”/src/res/version.num中。您给出的路径必须是相对于类路径的。e、 g.如果
target/classes/
在您的类中,则路径需要位于名为res.的子目录中,即target/classes/res/version.num
PAH。我不能让它工作。我的文件夹结构是,这是我的.classpath和当前代码,我怀疑您需要从路径中删除前导“/”。这在Tomcat中很有效,但在普通Java中可能不起作用。看我的例子。谢谢,谢谢,谢谢,。。。这么愚蠢的错误!我搜索了几个小时:(1000倍再次感谢