使用Apache Commons 2.1:

import org.apache.logging.log4j.core.util.FileUtils;

FileUtils.writeStringToFile(file, "String to append", true);

您这样做是为了记录日志吗?如果是这样，有几个库。其中最流行的两个是Log4j和Logback。

Java 7 +

对于一次性任务，Files类可以很容易地做到这一点:

try {
    Files.write(Paths.get("myfile.txt"), "the text".getBytes(), StandardOpenOption.APPEND);
}catch (IOException e) {
    //exception handling left as an exercise for the reader
}

注意:如果文件不存在，上述方法将抛出NoSuchFileException。它也不会自动追加换行符(当追加到文本文件时，您经常希望这样)。另一种方法是同时传递CREATE和APPEND选项，如果文件不存在，则会先创建文件:

private void write(final String s) throws IOException {
    Files.writeString(
        Path.of(System.getProperty("java.io.tmpdir"), "filename.txt"),
        s + System.lineSeparator(),
        CREATE, APPEND
    );
}

但是，如果要多次写入同一个文件，那么上面的代码段必须多次打开和关闭磁盘上的文件，这是一个缓慢的操作。在这种情况下，BufferedWriter会更快:

try(FileWriter fw = new FileWriter("myfile.txt", true);
    BufferedWriter bw = new BufferedWriter(fw);
    PrintWriter out = new PrintWriter(bw))
{
    out.println("the text");
    //more code
    out.println("more text");
    //more code
} catch (IOException e) {
    //exception handling left as an exercise for the reader
}

注:

FileWriter构造函数的第二个参数将告诉它追加到文件中，而不是写入一个新文件。(如果该文件不存在，将创建该文件。) 对于昂贵的写入器(如FileWriter)，建议使用BufferedWriter。 使用PrintWriter可以访问您可能在System.out中习惯的println语法。 但是BufferedWriter和PrintWriter包装器并不是严格必要的。

老Java

try {
    PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("myfile.txt", true)));
    out.println("the text");
    out.close();
} catch (IOException e) {
    //exception handling left as an exercise for the reader
}

异常处理

如果你需要对旧Java进行健壮的异常处理，它会变得非常冗长:

FileWriter fw = null;
BufferedWriter bw = null;
PrintWriter out = null;
try {
    fw = new FileWriter("myfile.txt", true);
    bw = new BufferedWriter(fw);
    out = new PrintWriter(bw);
    out.println("the text");
    out.close();
} catch (IOException e) {
    //exception handling left as an exercise for the reader
}
finally {
    try {
        if(out != null)
            out.close();
    } catch (IOException e) {
        //exception handling left as an exercise for the reader
    }
    try {
        if(bw != null)
            bw.close();
    } catch (IOException e) {
        //exception handling left as an exercise for the reader
    }
    try {
        if(fw != null)
            fw.close();
    } catch (IOException e) {
        //exception handling left as an exercise for the reader
    }
}

图书馆

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

代码

public void append()
{
    try
    {
        String path = "D:/sample.txt";

        File file = new File(path);

        FileWriter fileWriter = new FileWriter(file,true);

        BufferedWriter bufferFileWriter  = new BufferedWriter(fileWriter);

        fileWriter.append("Sample text in the file to append");

        bufferFileWriter.close();

        System.out.println("User Registration Completed");

    }catch(Exception ex)
    {
        System.out.println(ex);
    }
}

FileOutputStream fos = new FileOutputStream("File_Name", true);
fos.write(data);

true允许在现有文件中追加数据。如果我们写

FileOutputStream fos = new FileOutputStream("File_Name");

它将覆盖现有文件。所以选择第一种方法。

这里使用try/catch块的所有答案不都应该在finally块中包含.close()块吗?

有标记的答案示例:

PrintWriter out = null;
try {
    out = new PrintWriter(new BufferedWriter(new FileWriter("writePath", true)));
    out.println("the text");
} catch (IOException e) {
    System.err.println(e);
} finally {
    if (out != null) {
        out.close();
    }
} 

此外，从Java 7开始，您可以使用try-with-resources语句。关闭已声明的资源时不需要finally块，因为它是自动处理的，而且不太详细:

try(PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("writePath", true)))) {
    out.println("the text");
} catch (IOException e) {
    System.err.println(e);
}

尝试使用bufferFileWriter。附加，它对我有用。

FileWriter fileWriter;
try {
    fileWriter = new FileWriter(file,true);
    BufferedWriter bufferFileWriter = new BufferedWriter(fileWriter);
    bufferFileWriter.append(obj.toJSONString());
    bufferFileWriter.newLine();
    bufferFileWriter.close();
} catch (IOException ex) {
    Logger.getLogger(JsonTest.class.getName()).log(Level.SEVERE, null, ex);
}