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

如果您无权访问Files类,则可以使用本机解决方案。

static String readFile(File file, String charset)
        throws IOException
{
    FileInputStream fileInputStream = new FileInputStream(file);
    byte[] buffer = new byte[fileInputStream.available()];
    int length = fileInputStream.read(buffer);
    fileInputStream.close();
    return new String(buffer, 0, length, charset);
}

其他回答

一个灵活的解决方案,使用Apache commons io中的IOUItils和StringWriter:

Reader input = new FileReader();
StringWriter output = new StringWriter();
try {
  IOUtils.copy(input, output);
} finally {
  input.close();
}
String fileContents = output.toString();

它适用于任何读取器或输入流(不仅仅是文件),例如从URL读取时。

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

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);
}
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();
}

基于扫描仪的非常精简的解决方案:

Scanner scanner = new Scanner( new File("poem.txt") );
String text = scanner.useDelimiter("\\A").next();
scanner.close(); // Put this call in a finally block

或者,如果要设置字符集:

Scanner scanner = new Scanner( new File("poem.txt"), "UTF-8" );
String text = scanner.useDelimiter("\\A").next();
scanner.close(); // Put this call in a finally block

或者,使用trywithresources块,它将为您调用scanner.close():

try (Scanner scanner = new Scanner( new File("poem.txt"), "UTF-8" )) {
    String text = scanner.useDelimiter("\\A").next();
}

请记住,Scanner构造函数可以引发IOException。不要忘记导入java.io和java.util。

来源:Pat Niemeyer的博客