FileOutputStream stream = new FileOutputStream(path, true);
try {

    stream.write(

        string.getBytes("UTF-8") // Choose your encoding.

    );

} finally {
    stream.close();
}

然后在上游某处捕获IOException。

用番石榴做的样品:

File to = new File("C:/test/test.csv");

for (int i = 0; i < 42; i++) {
    CharSequence from = "some string" + i + "\n";
    Files.append(from, to, Charsets.UTF_8);
}

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
    }
}

这段代码将满足您的需要:

   FileWriter fw=new FileWriter("C:\\file.json",true);
   fw.write("ssssss");
   fw.close();

我建议你加入阿帕奇公共项目。这个项目已经提供了一个框架来做你需要的事情(即灵活的集合过滤)。

我只是补充了一个小细节:

    new FileWriter("outfilename", true)

2.nd parameter (true) is a feature (or, interface) called appendable (http://docs.oracle.com/javase/7/docs/api/java/lang/Appendable.html). It is responsible for being able to add some content to the end of particular file/stream. This interface is implemented since Java 1.5. Each object (i.e. BufferedWriter, CharArrayWriter, CharBuffer, FileWriter, FilterWriter, LogStream, OutputStreamWriter, PipedWriter, PrintStream, PrintWriter, StringBuffer, StringBuilder, StringWriter, Writer) with this interface can be used for adding content

换句话说，您可以向gzip文件或http进程添加一些内容