在java中怎样利用输出输入流累加写入一个记事本？

package com.cai;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.tree.DefaultMutableTreeNode;

import java.awt.*;
import java.awt.event.*;
import java.io.*;

class Remember extends JFrame implements TreeSelectionListener,ActionListener
{
JTree tree=null;
DefaultMutableTreeNode root;
JButton jb1=new JButton("保存");
JButton jb2=new JButton("删除");
JTextArea jta=new JTextArea(20,20);
DefaultMutableTreeNode month[]=new DefaultMutableTreeNode[13];
int i=0;
Remember()
{
Container con=getContentPane();
root=new DefaultMutableTreeNode("日历记事本");

for(i=1;i<=12;i++)
{
month[i]=new DefaultMutableTreeNode(" "+i+"月");
root.add(month[i]);
}
for(i=1;i<=12;i++)
{
if(i==1||i==3||i==5||i==7||i==8||i==10||i==12)
{
for(int j=1;j<=31;j++)
month[i].add(new DefaultMutableTreeNode(" "+j+"日"));
}
else if(i==4||i==6||i==9||i==11)
{
for(int j=1;j<30;j++)
month[i].add(new DefaultMutableTreeNode(" "+j+"日"));

}else
{
for(int j=1;j<28;j++)
{
month[i].add(new DefaultMutableTreeNode(" "+j+"日"));
}
}
}
jb1.addActionListener(this);
jb2.addActionListener(this);
tree=new JTree(root);
JPanel p=new JPanel();
p.setLayout(new BorderLayout());
JScrollPane scrollPane=new JScrollPane(jta);
p.add(scrollPane,BorderLayout.CENTER);
JPanel p1=new JPanel();
p1.add(jb1);
p1.add(jb2);
p.add(p1,BorderLayout.NORTH);
JScrollPane scrollPane2=new JScrollPane(tree);
JSplitPane splitpane=new JSplitPane(JSplitPane.HORIZONTAL_SPLIT,true,scrollPane2,p);
tree.addTreeSelectionListener(this);
con.add(splitpane);
setVisible(true);
setBounds(70,80,460,320);
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

}
public void valueChanged(TreeSelectionEvent e)
{
jta.setText(null);
if(e.getSource()==tree)
{
DefaultMutableTreeNode node=(DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
if(node.isLeaf())
{
String str=node.toString();
for(i=1;i<=12;i++)
{
if(node.getParent()==month[i])
{
try
{
String temp=null;
File f=new File("d:\\"+node.getParent().toString()+str+".txt");
FileReader fr=new FileReader(f);
BufferedReader in=new BufferedReader(fr);
while((temp=in.readLine())!=null)
{
jta.append(temp+"\n");
}

in.close();
fr.close();
}catch(Exception e1){e1.printStackTrace();}
}
}
}
}
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==jb1)
{
DefaultMutableTreeNode node=(DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
String str=node.toString();
System.out.println(str);
System.out.println(node.getParent().toString());
if(node.isLeaf())
{
try
{
File f=new File("d:\\"+node.getParent().toString()+str+".txt");
FileWriter fw=new FileWriter(f);
BufferedWriter bw=new BufferedWriter(fw);
bw.write(jta.getText(),0,(jta.getText()).length());
bw.flush();
//fw.close();
bw.close();
}catch(Exception e2){e2.printStackTrace();}
}

}
else if(e.getSource()==jb2)
{
DefaultMutableTreeNode node=(DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
try
{
String str=node.toString();
if(node.isLeaf())
{
File f=new File("d:\\"+node.getParent().toString()+str+".txt");
f.delete();
}
}catch(Exception e3){e3.printStackTrace();}
}
}

}
public class Test4
{
public static void main(String args[])
{
Remember win=new Remember();
win.validate();
}

}

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.InputEvent;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import javax.swing.BorderFactory;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.JPopupMenu;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.KeyStroke;
import javax.swing.ScrollPaneConstants;
import javax.swing.SwingConstants;

public class JNotePadUI extends JFrame {
private JMenuItem menuOpen;
private JMenuItem menuSave;
private JMenuItem menuSaveAs;
private JMenuItem menuClose;

private JMenu editMenu;
private JMenuItem menuCut;
private JMenuItem menuCopy;
private JMenuItem menuPaste;

private JMenuItem menuAbout;

private JTextArea textArea;
private JLabel stateBar;
private JFileChooser fileChooser;

private JPopupMenu popUpMenu;

public JNotePadUI() {
super("新建文本文件");
setUpUIComponent();
setUpEventListener();
setVisible(true);
}

private void setUpUIComponent() {
setSize(640, 480);

// 菜单栏
JMenuBar menuBar = new JMenuBar();

// 设置「文件」菜单
JMenu fileMenu = new JMenu("文件");
menuOpen = new JMenuItem("打开");
// 快捷键设置
menuOpen.setAccelerator(
KeyStroke.getKeyStroke(
KeyEvent.VK_O,
InputEvent.CTRL_MASK));
menuSave = new JMenuItem("保存");
menuSave.setAccelerator(
KeyStroke.getKeyStroke(
KeyEvent.VK_S,
InputEvent.CTRL_MASK));
menuSaveAs = new JMenuItem("另存为");

menuClose = new JMenuItem("关闭");
menuClose.setAccelerator(
KeyStroke.getKeyStroke(
KeyEvent.VK_Q,
InputEvent.CTRL_MASK));

fileMenu.add(menuOpen);
fileMenu.addSeparator(); // 分隔线
fileMenu.add(menuSave);
fileMenu.add(menuSaveAs);
fileMenu.addSeparator(); // 分隔线
fileMenu.add(menuClose);

// 设置「编辑」菜单
JMenu editMenu = new JMenu("编辑");
menuCut = new JMenuItem("剪切");
menuCut.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_X,
InputEvent.CTRL_MASK));
menuCopy = new JMenuItem("复制");
menuCopy.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_C,
InputEvent.CTRL_MASK));
menuPaste = new JMenuItem("粘贴");
menuPaste.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_V,
InputEvent.CTRL_MASK));
editMenu.add(menuCut);
editMenu.add(menuCopy);
editMenu.add(menuPaste);

// 设置「关于」菜单
JMenu aboutMenu = new JMenu("关于");
menuAbout = new JMenuItem("关于JNotePad");
aboutMenu.add(menuAbout);

menuBar.add(fileMenu);
menuBar.add(editMenu);
menuBar.add(aboutMenu);

setJMenuBar(menuBar);

// 文字编辑区域
textArea = new JTextArea();
textArea.setFont(new Font("宋体", Font.PLAIN, 16));
textArea.setLineWrap(true);
JScrollPane panel = new JScrollPane(textArea,
ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED,
ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);

Container contentPane = getContentPane();
contentPane.add(panel, BorderLayout.CENTER);

// 状态栏
stateBar = new JLabel("未修改");
stateBar.setHorizontalAlignment(SwingConstants.LEFT);
stateBar.setBorder(
BorderFactory.createEtchedBorder());
contentPane.add(stateBar, BorderLayout.SOUTH);

popUpMenu = editMenu.getPopupMenu();
fileChooser = new JFileChooser();
}

private void setUpEventListener() {
// 按下窗口关闭钮事件处理
addWindowListener(
new WindowAdapter() {
public void windowClosing(WindowEvent e) {
closeFile();
}
}
);

// 菜单 - 打开
menuOpen.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
openFile();
}
}
);

// 菜单 - 保存
menuSave.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
saveFile();
}
}
);

// 菜单 - 另存为
menuSaveAs.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
saveFileAs();
}
}
);

// 菜单 - 关闭文件
menuClose.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
closeFile();
}
}
);

// 菜单 - 剪切
menuCut.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
cut();
}
}
);

// 菜单 - 复制
menuCopy.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
copy();
}
}
);

// 菜单 - 粘贴
menuPaste.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
paste();
}
}
);

// 菜单 - 关于
menuAbout.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
// 显示对话框
JOptionPane.showOptionDialog(null,
"程序名称:\n JNotePad \n" +
"程序设计:\n \n" +
"简介:\n 一个简单的文字编辑器\n" +
" 可作为验收Java的实现对象\n" +
" 欢迎网友下载研究交流\n\n" +
" /",
"关于JNotePad",
JOptionPane.DEFAULT_OPTION,
JOptionPane.INFORMATION_MESSAGE,
null, null, null);
}
}
);

// 编辑区键盘事件
textArea.addKeyListener(
new KeyAdapter() {
public void keyTyped(KeyEvent e) {
processTextArea();
}
}
);

// 编辑区鼠标事件
textArea.addMouseListener(
new MouseAdapter() {
public void mouseReleased(MouseEvent e) {
if(e.getButton() == MouseEvent.BUTTON3)
popUpMenu.show(editMenu, e.getX(), e.getY());
}

public void mouseClicked(MouseEvent e) {
if(e.getButton() == MouseEvent.BUTTON1)
popUpMenu.setVisible(false);
}
}
);
}

private void openFile() {
if(isCurrentFileSaved()) { // 文件是否为保存状态
open(); // 打开
}
else {
// 显示对话框
int option = JOptionPane.showConfirmDialog(
null, "文件已修改，是否保存？",
"保存文件？", JOptionPane.YES_NO_OPTION,
JOptionPane.WARNING_MESSAGE, null);
switch(option) {
// 确认文件保存
case JOptionPane.YES_OPTION:
saveFile(); // 保存文件
break;
// 放弃文件保存
case JOptionPane.NO_OPTION:
open();
break;
}
}
}
private boolean isCurrentFileSaved() {
if(stateBar.getText().equals("未修改")) {
return false;
}
else {
return true;
}
}
private void open() {
// fileChooser 是 JFileChooser 的实例
// 显示文件选取的对话框
int option = fileChooser.showDialog(null, null);

// 使用者按下确认键
if(option == JFileChooser.APPROVE_OPTION) {
try {
// 开启选取的文件
BufferedReader buf =
new BufferedReader(
new FileReader(
fileChooser.getSelectedFile()));

// 设定文件标题
setTitle(fileChooser.getSelectedFile().toString());
// 清除前一次文件
textArea.setText("");
// 设定状态栏
stateBar.setText("未修改");
// 取得系统相依的换行字符
String lineSeparator = System.getProperty("line.separator");
// 读取文件并附加至文字编辑区
String text;
while((text = buf.readLine()) != null) {
textArea.append(text);
textArea.append(lineSeparator);
}

buf.close();
}
catch(IOException e) {
JOptionPane.showMessageDialog(null, e.toString(),
"开启文件失败", JOptionPane.ERROR_MESSAGE);
}
}
}
private void saveFile() {
// 从标题栏取得文件名称
File file = new File(getTitle());

// 若指定的文件不存在
if(!file.exists()) {
// 执行另存为
saveFileAs();
}
else {
try {
// 开启指定的文件
BufferedWriter buf =
new BufferedWriter(
new FileWriter(file));
// 将文字编辑区的文字写入文件
buf.write(textArea.getText());
buf.close();
// 设定状态栏为未修改
stateBar.setText("未修改");
}
catch(IOException e) {
JOptionPane.showMessageDialog(null, e.toString(),
"写入文件失败", JOptionPane.ERROR_MESSAGE);
}
}
}

private void saveFileAs() {
// 显示文件对话框
int option = fileChooser.showSaveDialog(null);

// 如果确认选取文件
if(option == JFileChooser.APPROVE_OPTION) {
// 取得选择的文件
File file = fileChooser.getSelectedFile();

// 在标题栏上设定文件名称
setTitle(file.toString());

try {
// 建立文件
file.createNewFile();
// 进行文件保存
saveFile();
}
catch(IOException e) {
JOptionPane.showMessageDialog(null, e.toString(),
"无法建立新文件", JOptionPane.ERROR_MESSAGE);
}
}
}

private void closeFile() {
// 是否已保存文件
if(isCurrentFileSaved()) {
// 释放窗口资源，而后关闭程序
dispose();
}
else {
int option = JOptionPane.showConfirmDialog(
null, "文件已修改，是否保存？",
"保存文件？", JOptionPane.YES_NO_OPTION,
JOptionPane.WARNING_MESSAGE, null);

switch(option) {
case JOptionPane.YES_OPTION:
saveFile();
break;
case JOptionPane.NO_OPTION:
dispose();
}
}
}

private void cut() {
textArea.cut();
stateBar.setText("已修改");
popUpMenu.setVisible(false);
}

private void copy() {
textArea.copy();
popUpMenu.setVisible(false);
}

private void paste() {
textArea.paste();
stateBar.setText("已修改");
popUpMenu.setVisible(false);
}

private void processTextArea() {
stateBar.setText("已修改");
}

public static void main(String[] args) {
new JNotePadUI();
}
}本回答被提问者和网友采纳

可以先将原来的内容读出来在写进去，或者直接查附加到文件尾的API