Question

我已编写此代码用于从类路径中读取文件，现在我想在类路径内的同一文件中编写。请告诉我该怎么做？

import java.io.InputStream;
import java.io.InputStreamReader;

import javax.swing.JOptionPane;



public class A {

    public A() throws Exception {

        final InputStream inputStream = A.class.getResourceAsStream("f/file.txt");
        final InputStreamReader r = new InputStreamReader(inputStream);

        int end;
        String out="";

        while((end=r.read())!=-1)
            out+=(char)end;

        JOptionPane.showMessageDialog(null, out);
    }

    public static void main(String arg[] ) throws Exception {
        new A();
    }
}

Answer 1

如果您尝试写入的文件位于JAR中，则无法正常工作，但通常情况下，您可以检索资源的URL，然后使用该URL写入。

URL url = A.class.getResource("f/file.txt");
File f = new File(url.toURI().getPath());

// binary data
FileOutputStream fos = new FileOutputStream(f);
fos.write( /* data */ );
fos.close();

// OR text
FileWriter fw = new FileWriter(f.getAbsoluteFile());
BufferedWriter bw = new BufferedWriter(fw);
bw.write( /* data */ );
bw.close();

但请记住要小心，文件实际上可以写入。

Answer 2

如果要记录玩家分数，则必须将其保存在文件中（每个示例中为highscores.dat）。在我查看内容的方式中，您无法在.jar文件中记录，因为de系统正在使用它。

对于记录，您可以创建一个包含一个游戏的高分的类，然后创建一个包含全部高分的数组。

class HighScoreRecord implements java.io.Serializable {

        private static final long serialVersionUID = 1L;

        private final String name;
        private final int highScore;

        HighScoreRecord( String name, int highScore ){
            this.name = name;
            this.highScore = highScore;
        }
}

别忘了实现java.io.Serializable，否则你将无法保存它。并且不要忘记创建一个长类型的私有静态字段＆＃34; serialVersionUID＆＃34;因为如果没有JVM，它可以归属自己的序列，并且它可能导致与已经记录的文件不兼容。

HighScoreRecord[] highscores = new HighScoreRecord[]{ 
    new HighScoreRecord( "Player1", 1000 ), 
    new HighScoreRecord( "Player2", 800 ), 
    new HighScoreRecord( "Player3", 600 ), 
    new HighScoreRecord( "Player4", 400 ), 
    new HighScoreRecord( "Player5", 200 ) 
};

保存记录：

private void writeHighScores() {

    FileOutputStream fileOutput = null;
    ObjectOutputStream save = null;

    try {
        //HIGH_SCORES_FILE is any object of type File
        fileOutput = new FileOutputStream( HIGH_SCORES_FILE );
        save = new ObjectOutputStream( fileOutput );

        save.writeObject( highscores );
    }
    catch ( FileNotFoundException ex ) {
        //Exception handling
    }
    catch ( IOException ex ) {
        //Exception handling
    }
    finally {

        if( save != null )
            try{
                save.close();
            } catch ( IOException ex ) { 
                //Exception handling
            }

        if( fileOutput != null )
            try{
                fileOutput.close();
            } catch ( IOException ex ) { 
                //Exception handling
            }

    }
}

修改

加载：

HighScoreRecord[] high = null; FileInputStream fileInput = null; ObjectInputStream load = null; try { fileInput = new FileInputStream( HIGH_SCORES_FILE ); load = new ObjectInputStream( fileInput ); high = (HighScoreRecord[]) load.readObject(); } catch ( FileNotFoundException ex ) { //Exception handling } catch ( IOException | ClassNotFoundException ex ) { //Exception handling } finally { if( load != null ) try{ load.close(); } catch ( IOException ex ) { //Exception handling } if( fileInput != null ) try{ fileInput.close(); } catch ( IOException ex ) { //Exception handling } } highscores = high;

我希望我有所帮助。

Answer 3

如果您的应用程序类路径指向您可以写入访问权限的目录，那么在该目录中创建文件后，可以将其作为资源加载。

如果你的类路径中没有目录，你可以创建一个指向目录的类加载器。

此外，如果您使用的是Java 7及更高版本，则应该利用the Path API以及the try-with-resources language feature，这样可以使代码更小，更少错误修剪。

以下是一个例子：

public class FileIO {

    public static void main(String[] args) throws IOException {
        Path tmpDir = Files.createTempDirectory("test");
        String string = "My data";
        Path file = tmpDir.resolve("myfile.txt");
        System.out.println("File created: " + file);

        Files.write(file, string.getBytes());

        String myString = new String(Files.readAllBytes(file));
        System.out.println("Read from file: " + myString);

        URLClassLoader classLoader = new URLClassLoader(new URL[]{tmpDir.toUri().toURL()});
        try (InputStream stream = classLoader.getResourceAsStream("myfile.txt");
             BufferedReader reader = new BufferedReader(new InputStreamReader(stream))) {
            System.out.println("Read from class loader: " + reader.readLine());
        }
    }
}

输出：

File created: /var/folders/97/63hj35sn6wb0tmcnkrhf5b040000gn/T/test3343347264203608746/myfile.txt
Read from file: My data
Read from class loader: My data

在java中写入classpath中的文件

3 个答案: