我已经用下面这个成语有一段时间了。这似乎是传播最广的,至少在我访问过的网站上。

在Java中有没有更好/不同的方法将文件读入字符串?

private String readFile(String file) throws IOException {
    BufferedReader reader = new BufferedReader(new FileReader (file));
    String         line = null;
    StringBuilder  stringBuilder = new StringBuilder();
    String         ls = System.getProperty("line.separator");

    try {
        while((line = reader.readLine()) != null) {
            stringBuilder.append(line);
            stringBuilder.append(ls);
        }

        return stringBuilder.toString();
    } finally {
        reader.close();
    }
}

当前回答

将文件读取为二进制文件并在末尾转换

public static String readFileAsString(String filePath) throws IOException {
    DataInputStream dis = new DataInputStream(new FileInputStream(filePath));
    try {
        long len = new File(filePath).length();
        if (len > Integer.MAX_VALUE) throw new IOException("File "+filePath+" too large, was "+len+" bytes.");
        byte[] bytes = new byte[(int) len];
        dis.readFully(bytes);
        return new String(bytes, "UTF-8");
    } finally {
        dis.close();
    }
}

其他回答

自JDK 11以来:

String file = ...
Path path = Paths.get(file);
String content = Files.readString(path);
// Or readString(path, someCharset), if you need a Charset different from UTF-8

对于Java 7,这是我读取UTF-8文件的首选选项:

String content = new String(Files.readAllBytes(Paths.get(filename)), "UTF-8");

自Java7以来,JDK有了新的Java.nio.file API,它提供了许多快捷方式,因此简单的文件操作并不总是需要第三方库。


由于人们仍然对这个答案投赞成票,这里有一个在Java 11中引入的更好的解决方案:

String content = Files.readString(path);

同一主题上有一个变体,它使用for循环而不是while循环来限制行变量的范围。是否“更好”取决于个人品味。

for(String line = reader.readLine(); line != null; line = reader.readLine()) {
    stringBuilder.append(line);
    stringBuilder.append(ls);
}

在一行(Java 8)中,假设您有一个Reader:

String sMessage = String.join("\n", reader.lines().collect(Collectors.toList()));
public static String slurp (final File file)
throws IOException {
    StringBuilder result = new StringBuilder();

    BufferedReader reader = new BufferedReader(new FileReader(file));

    try {
        char[] buf = new char[1024];

        int r = 0;

        while ((r = reader.read(buf)) != -1) {
            result.append(buf, 0, r);
        }
    }
    finally {
        reader.close();
    }

    return result.toString();
}