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

如果您愿意使用外部库,请查看ApacheCommonsIO(200KBJAR)。它包含一个org.apache.commons.io.FileUtils.readFileToString()方法,该方法允许您用一行代码将整个文件读取为字符串。

例子:

import java.io.*;
import java.nio.charset.*;
import org.apache.commons.io.*;

public String readFile() throws IOException {
    File file = new File("data.txt");
    return FileUtils.readFileToString(file, StandardCharsets.UTF_8);
}

其他回答

此外,如果您的文件恰好位于jar中,您也可以使用此选项:

public String fromFileInJar(String path) {
    try ( Scanner scanner 
            = new Scanner(getClass().getResourceAsStream(path))) {
        return scanner.useDelimiter("\\A").next();
    }
}

例如,如果您的jar是

my.jar/com/some/thing/a.txt

然后你想这样调用它:

String myTxt = fromFileInJar("/com/com/thing/a.txt");

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();
    }
}

根据@erickson的回答,您可以使用:

public String readAll(String fileName) throws IOException {
    List<String> lines = Files.readAllLines(new File(fileName).toPath());
    return String.join("\n", lines.toArray(new String[lines.size()]));
}

这一个使用RandomAccessFile.readFully方法,它似乎可以从JDK 1.0中获得!

public static String readFileContent(String filename, Charset charset) throws IOException {
    RandomAccessFile raf = null;
    try {
        raf = new RandomAccessFile(filename, "r");
        byte[] buffer = new byte[(int)raf.length()];
        raf.readFully(buffer);
        return new String(buffer, charset);
    } finally {
        closeStream(raf);
    }
} 


private static void closeStream(Closeable c) {
    if (c != null) {
        try {
            c.close();
        } catch (IOException ex) {
            // do nothing
        }
    }
}

使用代码:

File file = new File("input.txt");
BufferedInputStream bin = new BufferedInputStream(new FileInputStream(
                file));
byte[] buffer = new byte[(int) file.length()];
bin.read(buffer);
String fileStr = new String(buffer);

fileStr包含字符串形式的输出。