类似于Python的Java IO库？

Question

Java 不是我主要使用的编程语言，所以我可能问的问题很简单。

但是在 Java 中有没有像 Python 那样简单的文件处理库呢？

举个例子，我只想这样做：

File f = Open('file.txt', 'w')
for(String line:f){
      //do something with the line from file
}

谢谢！

更新：好吧，stackoverflow 自动接受了一个奇怪的答案。这和我设置的悬赏有关——所以如果你想看看其他答案，只需往下滚动即可！

Answer 1

如果你已经在用Apache commons lang和commons io这两个库，那么这可能是一个替代方案：

String[] lines = StringUtils.split(FileUtils.readFileToString(new File("myfile.txt")), '\n');
for(String line: lines){
      //do something with the line from file
}

（我更喜欢Jesper的回答）

Answer 2

在Java中逐行读取文件的方法：

BufferedReader in = new BufferedReader(new FileReader("myfile.txt"));

String line;
while ((line = in.readLine()) != null) {
    // Do something with this line
    System.out.println(line);
}

in.close();

大部分与输入输出相关的类都在java.io这个包里。你可以查看这个包的API文档。想要了解更多详细信息，可以看看Sun的Java I/O教程。

补充说明：上面的例子会使用你系统的默认字符编码来读取文本文件。如果你想明确指定字符编码，比如UTF-8，可以把第一行改成这样：

BufferedReader in = new BufferedReader(
    new InputStreamReader(new FileInputStream("myfile.txt"), "UTF-8"));

Answer 3

我在想的其实是这样的：

File f = File.open("C:/Users/File.txt");

for(String s : f){
   System.out.println(s);
}

这是我的源代码：

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.Iterator;

public abstract class File implements Iterable<String>{
    public final static String READ = "r";
    public final static String WRITE = "w";

    public static File open(String filepath) throws IOException{
        return open(filepath, READ);
    }   

    public static File open(String filepath, String mode) throws IOException{
    if(mode == READ){
        return new ReadableFile(filepath);
    }else if(mode == WRITE){
        return new WritableFile(filepath);
    }
    throw new IllegalArgumentException("Invalid File Write mode '" + mode + "'");
    }

    //common methods
    public abstract void close() throws IOException;

    // writer specific
    public abstract void write(String s) throws IOException;

}

class WritableFile extends File{
    String filepath;
    Writer writer;

    public WritableFile(String filepath){
        this.filepath = filepath;
    }

    private Writer writer() throws IOException{
        if(this.writer == null){
            writer = new BufferedWriter(new FileWriter(this.filepath));
        }
        return writer;
    }

    public void write(String chars) throws IOException{
        writer().write(chars);
    }

    public void close() throws IOException{
        writer().close();
    }

    @Override
    public Iterator<String> iterator() {        
        return null;
    }
}

class ReadableFile extends File implements Iterator<String>{
    private BufferedReader reader;
    private String line;    
    private String read_ahead;

    public ReadableFile(String filepath) throws IOException{        
        this.reader = new BufferedReader(new FileReader(filepath)); 
        this.read_ahead = this.reader.readLine();
    }

    private Reader reader() throws IOException{
         if(reader == null){
               reader = new BufferedReader(new FileReader(filepath));   
         }
         return reader;
    }

    @Override
    public Iterator<String> iterator() {
        return this;
    }

    @Override
    public void close() throws IOException {
        reader().close();
    }

    @Override
    public void write(String s) throws IOException {
        throw new IOException("Cannot write to a read-only file.");
    }

    @Override
    public boolean hasNext() {      
        return this.read_ahead != null;
    }

    @Override
    public String next() {
        if(read_ahead == null)
            line = null;
        else
            line = new String(this.read_ahead);

        try {
            read_ahead = this.reader.readLine();
        } catch (IOException e) {
            read_ahead = null;
            reader.close()
        }
        return line;
    }

    @Override
    public void remove() {
        // do nothing       
    }
}

还有这是它的单元测试：

import java.io.IOException;
import org.junit.Test;

public class FileTest {
    @Test
    public void testFile(){
        File f;
        try {
            f = File.open("File.java");
            for(String s : f){
                System.out.println(s);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void testReadAndWriteFile(){
        File from;
        File to;
        try {
            from = File.open("File.java");
            to = File.open("Out.txt", "w");
            for(String s : from){           
                to.write(s + System.getProperty("line.separator"));
            }
            to.close();
        } catch (IOException e1) {
            e1.printStackTrace();
        }   
    }
}