Java - 从文本文件获取 ArrayList 内容并输出到单独的行(JavaMail API)

Question

我正在尝试读取具有多行文本的文本文件。现在我想将其输出到控制台，一次一行，因为这是文本文件的格式。很容易，对吧？我们可以用一个简单的 for 循环来做到这一点，如下所示:

lineList.forEach(System.out::println),

现在的问题是，我实际上正在使用JavaMail API，特别是访问仅接受String类型的message.setText方法。

我想知道如何在 setText 方法中将 ArrayList 输出到单独的行。我在想也许可以将该 for 循环存储为变量并在方法中调用它？

ArrayList<String> lineList = new ArrayList<>();

// New BufferedReader.
    BufferedReader reader = new BufferedReader(new FileReader(
            file));

    // Add all lines from file to ArrayList.
    while (true) {
        String line = reader.readLine();
        if (line == null) {
            break;
        }
        lineList.add(line);
    }

    // Close it.
    reader.close();

    // Print each line.
    for (String line : lineList) {
        System.out.println(line);
    }

// SetText method from the JavaMail API that does not accept the for-loop  
message.setText(lineList.forEach(System.out::println);

Answer 1

如果我查看此 JavaDoc ( https://javamail.java.net/nonav/docs/api/javax/mail/Part.html )，我认为这应该有效:

// New BufferedReader.
BufferedReader reader = new BufferedReader(new FileReader(file));

// Add all lines from file to ArrayList.
while (true){
    String line = reader.readLine();
    if(line==null){
        break;
    }
    lineList.add(line);
}

// Close it.
reader.close();

StringBuilder sb = new StringBuilder();

// Print each line.
for (String line : lineList){
    sb.append(line);
}

// SetText method from the JavaMail API that does not accept the for-loop  
message.setText(sb.toString());