将文件从src文件夹加载到阅读器中
我想知道如何从src文件夹lol.txt文件lol.txt加载到我的close方法中。 到目前为止的代码：
public void close() throws IOException { boolean loadFromClasspath = true; String fileName = "..."; // provide an absolute path here to be sure that file is found BufferedReader reader = null; try { if (loadFromClasspath) { // loading from classpath // see the link above for more options InputStream in = getClass().getClassLoader().getResourceAsStream("lol.txt"); reader = new BufferedReader(new InputStreamReader(in)); } else { // load from file system reader = new BufferedReader(new FileReader(new File(fileName))); } String line = null; while ( (line = reader.readLine()) != null) { // do something with the line here System.out.println("Line read: " + line); } } catch (IOException e) { JOptionPane.showMessageDialog(null,e.getMessage()+" for lol.txt","File Error",JOptionPane.ERROR_MESSAGE); } finally { if (reader != null) { reader.close(); } } }
启动时控制台错误输出：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at java.io.Reader.(Unknown Source) at java.io.InputStreamReader.(Unknown Source) at main.main.close(main.java:191) at main.main$1.windowClosing(main.java:24) at java.awt.Window.processWindowEvent(Unknown Source) at javax.swing.JFrame.processWindowEvent(Unknown Source) at java.awt.Window.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$000(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source)
如果您想从jar文件（即从类路径）加载文件，请参阅此答案以获取有关如何获取InputStream更多选项。 在下面的代码中，我遗漏了exception处理并删除了Random相关代码。
public void close() { boolean loadFromClasspath = true; String fileName = "..."; // provide an absolute path here to be sure that file is found BufferedReader reader = null; try { if (loadFromClasspath) { // loading from classpath // see the link above for more options InputStream in = getClass().getClassLoader().getResourceAsStream("absolute/path/to/file/inside/jar/lol.txt"); reader = new BufferedReader(new InputStreamReader(in)); } else { // load from file system reader = new BufferedReader(new FileReader(new File(fileName))); } String line = null; while ( (line = reader.readLine()) != null) { // do something with the line here System.out.println("Line read: " + line); } } catch (IOException e) { JOptionPane.showMessageDialog(null,e.getMessage()+" for lol.txt","File Error",JOptionPane.ERROR_MESSAGE); } finally { if (reader != null) { reader.close(); } } }
编辑：您似乎正在对文件夹结构执行错误操作，或者您使用了错误的包/文件名。 只是要清楚。 目前，您似乎在main包下面有一个名为main的类。 您的文件夹结构应该是这样的：
+ src/ + main/ main.java lol.txt
当你编译时，你的lol.txt文件（顺便说一句，那些是小写的L而不是数字1对吗？）应该复制到/bin/main/文件夹下
如果是这种情况，那么使用如下代码： InputStream in = getClass().getClassLoader().getResourceAsStream("main/lol.txt");
如果您的文件夹结构不同，请相应更改
如果要从类路径获取文件（资源）的InputStream ，可以执行以下操作
InputStream in = this.getClass().getResourceAsStream("lol.txt");
假设名为lol.txt的资源与getClass()表示并返回的类位于同一个包中。
如果资源不在同一个包中，则可以在路径前加上/ ，告诉方法查看类路径的根。
InputStream in = this.getClass().getResourceAsStream("/lol.txt"); // or /some/resource/path/lol.txt for some other path starting at root of classpath
如果您尝试从static方法访问资源，则无法访问this 。 你需要使用
YourClass.class.getResourceAsStream("/lol.txt");
在这里阅读javadoc。