在项目的任何地方创建一个函数，并在任何需要的地方简单地调用该函数。

伙计们，你们要记住，你们调用的是活动线程，而不是异步调用，因为它可能需要5到10页才能完成。 为什么不花更多的时间在你的项目上，忘掉已经写好的东西。 正确

    //Adding a static modifier would make this accessible anywhere in your app

    public Logger getLogger()
    {
       return java.util.logging.Logger.getLogger("MyLogFileName");
    }
    //call the method anywhere and append what you want to log 
    //Logger class will take care of putting timestamps for you
    //plus the are ansychronously done so more of the 
    //processing power will go into your application

    //from inside a function body in the same class ...{...

    getLogger().log(Level.INFO,"the text you want to append");

    ...}...
    /*********log file resides in server root log files********/

三行代码，实际上是两行，因为第三行实际上是追加文本。: P

您可以使用fileWriter将标志设置为true，用于追加。

try
{
    String filename= "MyFile.txt";
    FileWriter fw = new FileWriter(filename,true); //the true will append the new data
    fw.write("add a line\n");//appends the string to the file
    fw.close();
}
catch(IOException ioe)
{
    System.err.println("IOException: " + ioe.getMessage());
}

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);
}

如果我们使用Java 7及以上版本，并且也知道要添加(追加)到文件的内容，我们可以使用NIO包中的newBufferedWriter方法。

public static void main(String[] args) {
    Path FILE_PATH = Paths.get("C:/temp", "temp.txt");
    String text = "\n Welcome to Java 8";

    //Writing to the file temp.txt
    try (BufferedWriter writer = Files.newBufferedWriter(FILE_PATH, StandardCharsets.UTF_8, StandardOpenOption.APPEND)) {
        writer.write(text);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

这里有几点需要注意:

指定字符集编码总是一个好习惯，为此我们在StandardCharsets类中有常量。 代码使用try-with-resource语句，其中资源在try之后自动关闭。

虽然OP没有要求，但以防我们想要搜索具有特定关键字的行，例如confidential，我们可以在Java中使用流api:

//Reading from the file the first line which contains word "confidential"
try {
    Stream<String> lines = Files.lines(FILE_PATH);
    Optional<String> containsJava = lines.filter(l->l.contains("confidential")).findFirst();
    if(containsJava.isPresent()){
        System.out.println(containsJava.get());
    }
} catch (IOException e) {
    e.printStackTrace();
}

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);
}

稍微扩展一下基普的回答， 下面是一个简单的Java 7+方法来追加一个新行到一个文件，如果它不存在就创建它:

try {
    final Path path = Paths.get("path/to/filename.txt");
    Files.write(path, Arrays.asList("New line to append"), StandardCharsets.UTF_8,
        Files.exists(path) ? StandardOpenOption.APPEND : StandardOpenOption.CREATE);
} catch (final IOException ioe) {
    // Add your own exception handling...
}

进一步指出:

The above uses the Files.write overload that writes lines of text to a file (i.e. similar to a println command). To just write text to the end (i.e. similar to a print command), an alternative Files.write overload can be used, passing in a byte array (e.g. "mytext".getBytes(StandardCharsets.UTF_8)). The CREATE option will only work if the specified directory already exists - if it doesn't, a NoSuchFileException is thrown. If required, the following code could be added after setting path to create the directory structure: Path pathParent = path.getParent(); if (!Files.exists(pathParent)) { Files.createDirectories(pathParent); }