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有关Java如何读写txt文件这个问题经常在面试时会被问到，不懂或不熟悉的同志们可是要记好了哟!先来看下具体实现吧! package common; import java.io.*; import java.util.ArrayList; public class IOTest { public static void main (String args[]) { ReadDate(); WriteDate(); } /** * 读取数据 */ public static void ReadDate() { String url = “e:/2.txt”; try { FileReader read = new FileReader(new File(url)); StringBuffer sb = new StringBuffer(); char ch[] = new char[1024]; int d = read.read(ch); while(d!=-1){ String str = new String(ch,0,d); sb.append(str); d = read.read(ch); } System.out.print(sb.toString()); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } /** * 写入数据 */ public static void WriteDate() { try{ File file = new File(“D:/abc.txt”); if (file.exists()) { file.delete(); } file.createNewFile(); BufferedWriter output = new BufferedWriter(new FileWriter(file)); ArrayList ResolveList = new ArrayList(); for (int i = 0; i 10; i++) { ResolveList.add(Math.random()* 100); } for (int i=0 ;i output.write(String.valueOf(ResolveList.get(i)) + “\n”); } output.close(); } catch (Exception ex) { System.out.println(ex); } } }
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import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
public class Io{
public static void main(String [] s){
File filename = new File("F:\\suncity.txt");
String filein="你好！";
RandomAccessFile mm = null;
try {
mm = new RandomAccessFile(filename,"rw");
mm.writeBytes(filein);
} catch (IOException e1) {
// TODO 自动生成 catch 块
e1.printStackTrace();
} finally{
if(mm!=null){
try {
mm.close();
} catch (IOException e2) {
// TODO 自动生成 catch 块
e2.printStackTrace();
}
}
}
}
}
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
/**
文件名：FileEncrypter.java
JDK：1.40以上
说明：文件加密
加密方法：三重DES加密
加密过程：对选中的文件加密后在同文件夹下生成一个增加了".tdes"
扩展名的加密文件
解密过程：对选中的加密文件（必须有".tdes"扩展名）进行解密
*/
public class FileEncrypter extends JFrame{
public static final int WIDTH = 550;
public static final int HEIGHT = 200;
public static void main(String args[]) {
FileEncrypter fe = new FileEncrypter();
fe.show();
}
FileEncrypter(){
this.setSize(WIDTH,HEIGHT);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setResizable(false);
Toolkit tk = Toolkit.getDefaultToolkit();
Dimension screenSize = tk.getScreenSize();
this.setLocation((screenSize.width - WIDTH)/2,
(screenSize.height - HEIGHT)/2);
this.setTitle("文件加密器(TriDES)");
Container c = this.getContentPane();
c.setLayout( new FlowLayout());
final FilePanel fp = new FilePanel("文件选择");
c.add(fp);
final KeyPanel pp = new KeyPanel("密码");
c.add(pp);
JButton jbE = new JButton("加密");
c.add(jbE);
jbE.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent event){
File file = new File(fp.getFileName());
if (file.exists())
encrypt(file.getAbsoluteFile(),pp.getKey());
else
JOptionPane.showMessageDialog(
null,"请选择文件！","提示",JOptionPane.OK_OPTION);
}
});
JButton jbD = new JButton("解密");
c.add(jbD);
jbD.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent event){
File file = new File(fp.getFileName());
if (file.exists())
decrypt(file.getAbsoluteFile(),pp.getKey());
else
JOptionPane.showMessageDialog(
null,"请选择文件！","提示",JOptionPane.OK_OPTION);
}
});
}
/**
加密函数
输入：
要加密的文件，密码（由0-F组成，共48个字符，表示3个8位的密码）如：
AD67EA2F3BE6E5ADD368DFE03120B5DF92A8FD8FEC2F0746
其中：
AD67EA2F3BE6E5AD DES密码一
D368DFE03120B5DF DES密码二
92A8FD8FEC2F0746 DES密码三
输出：
对输入的文件加密后，保存到同一文件夹下增加了".tdes"扩展名的文件中。
*/
private void encrypt(File fileIn,String sKey){
try{
if(sKey.length() == 48){
byte[] bytK1 = getKeyByStr(sKey.substring(0,16));
byte[] bytK2 = getKeyByStr(sKey.substring(16,32));
byte[] bytK3 = getKeyByStr(sKey.substring(32,48));
FileInputStream fis = new FileInputStream(fileIn);
byte[] bytIn = new byte[(int)fileIn.length()];
for(int i = 0;iFILEIN.LENGTH();I++){
bytIn[i] = (byte)fis.read();
}
//加密
byte[] bytOut = encryptByDES(encryptByDES(
encryptByDES(bytIn,bytK1),bytK2),bytK3);
String fileOut = fileIn.getPath() + ".tdes";
FileOutputStream fos = new FileOutputStream(fileOut);
for(int i = 0;iBYTOUT.LENGTH;I++){
fos.write((int)bytOut[i]);
}
fos.close();
JOptionPane.showMessageDialog(
this,"加密成功！","提示",JOptionPane.OK_OPTION);
}else
JOptionPane.showMessageDialog(
this,"密码长度必须等于48！","错误信息",JOptionPane.ERROR_MESSAGE);
}catch(Exception e){
e.printStackTrace();
}
}
/**
解密函数
输入：
要解密的文件，密码（由0-F组成，共48个字符，表示3个8位的密码）如：
AD67EA2F3BE6E5ADD368DFE03120B5DF92A8FD8FEC2F0746
其中：
AD67EA2F3BE6E5AD DES密码一
D368DFE03120B5DF DES密码二
92A8FD8FEC2F0746 DES密码三
输出：
对输入的文件解密后，保存到用户指定的文件中。
*/
private void decrypt(File fileIn,String sKey){
try{
if(sKey.length() == 48){
String strPath = fileIn.getPath();
if(strPath.substring(strPath.length()-5).toLowerCase().equals(".tdes"))
strPath = strPath.substring(0,strPath.length()-5);
else{
JOptionPane.showMessageDialog(
this,"不是合法的加密文件！","提示",JOptionPane.OK_OPTION);
return;
}
JFileChooser chooser = new JFileChooser();
chooser.setCurrentDirectory(new File("."));
chooser.setSelectedFile(new File(strPath));
//用户指定要保存的文件
int ret = chooser.showSaveDialog(this);
if(ret==JFileChooser.APPROVE_OPTION){
byte[] bytK1 = getKeyByStr(sKey.substring(0,16));
byte[] bytK2 = getKeyByStr(sKey.substring(16,32));
byte[] bytK3 = getKeyByStr(sKey.substring(32,48));
FileInputStream fis = new FileInputStream(fileIn);
byte[] bytIn = new byte[(int)fileIn.length()];
for(int i = 0;iFILEIN.LENGTH();I++){
bytIn[i] = (byte)fis.read();
}
//解密
byte[] bytOut = decryptByDES(decryptByDES(
decryptByDES(bytIn,bytK3),bytK2),bytK1);
File fileOut = chooser.getSelectedFile();
fileOut.createNewFile();
FileOutputStream fos = new FileOutputStream(fileOut);
for(int i = 0;iBYTOUT.LENGTH;I++){
fos.write((int)bytOut[i]);
}
fos.close();
JOptionPane.showMessageDialog(
this,"解密成功！","提示",JOptionPane.OK_OPTION);
}
}else
JOptionPane.showMessageDialog(
this,"密码长度必须等于48！","错误信息",JOptionPane.ERROR_MESSAGE);
}catch(Exception e){
JOptionPane.showMessageDialog(
this,"解密失败，请核对密码！","提示",JOptionPane.OK_OPTION);
}
}
/**
用DES方法加密输入的字节
bytKey需为8字节长，是加密的密码
*/
private byte[] encryptByDES(byte[] bytP,byte[] bytKey) throws Exception{
DESKeySpec desKS = new DESKeySpec(bytKey);
SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
SecretKey sk = skf.generateSecret(desKS);
Cipher cip = Cipher.getInstance("DES");
cip.init(Cipher.ENCRYPT_MODE,sk);
return cip.doFinal(bytP);
}
/**
用DES方法解密输入的字节
bytKey需为8字节长，是解密的密码
*/
private byte[] decryptByDES(byte[] bytE,byte[] bytKey) throws Exception{
DESKeySpec desKS = new DESKeySpec(bytKey);
SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
SecretKey sk = skf.generateSecret(desKS);
Cipher cip = Cipher.getInstance("DES");
cip.init(Cipher.DECRYPT_MODE,sk);
return cip.doFinal(bytE);
}
/**
输入密码的字符形式，返回字节数组形式。
如输入字符串：AD67EA2F3BE6E5AD
返回字节数组：{173,103,234,47,59,230,229,173}
*/
private byte[] getKeyByStr(String str){
byte[] bRet = new byte[str.length()/2];
for(int i=0;iSTR.LENGTH()
Integer itg =
new Integer(16*getChrInt(str.charAt(2*i)) + getChrInt(str.charAt(2*i+1)));
bRet[i] = itg.byteValue();
}
return bRet;
}
/**
计算一个16进制字符的10进制值
输入：0-F
*/
private int getChrInt(char chr){
int iRet=0;
if(chr=="0".charAt(0)) iRet = 0;
if(chr=="1".charAt(0)) iRet = 1;
if(chr=="2".charAt(0)) iRet = 2;
if(chr=="3".charAt(0)) iRet = 3;
if(chr=="4".charAt(0)) iRet = 4;
if(chr=="5".charAt(0)) iRet = 5;
if(chr=="6".charAt(0)) iRet = 6;
if(chr=="7".charAt(0)) iRet = 7;
if(chr=="8".charAt(0)) iRet = 8;
if(chr=="9".charAt(0)) iRet = 9;
if(chr=="A".charAt(0)) iRet = 10;
if(chr=="B".charAt(0)) iRet = 11;
if(chr=="C".charAt(0)) iRet = 12;
if(chr=="D".charAt(0)) iRet = 13;
if(chr=="E".charAt(0)) iRet = 14;
if(chr=="F".charAt(0)) iRet = 15;
return iRet;
}
}
/**
文件选择组件。
*/
class FilePanel extends JPanel{
FilePanel(String str){
JLabel label = new JLabel(str);
JTextField fileText = new JTextField(35);
JButton chooseButton = new JButton("浏览...");
this.add(label);
this.add(fileText);
this.add(chooseButton);
clickAction ca = new clickAction(this);
chooseButton.addActionListener(ca);
}
public String getFileName(){
JTextField jtf = (JTextField)this.getComponent(1);
return jtf.getText();
}
private class clickAction implements ActionListener{
clickAction(Component c){
cmpt = c;
}
public void actionPerformed(ActionEvent event){
JFileChooser chooser = new JFileChooser();
chooser.setCurrentDirectory(new File("."));
int ret = chooser.showOpenDialog(cmpt);
if(ret==JFileChooser.APPROVE_OPTION){
JPanel jp = (JPanel)cmpt;
JTextField jtf = (JTextField)jp.getComponent(1);
jtf.setText(chooser.getSelectedFile().getPath());
}
}
private Component cmpt;
}
}
/**
密码生成组件。
*/
class KeyPanel extends JPanel{
KeyPanel(String str){
JLabel label = new JLabel(str);
JTextField fileText = new JTextField(35);
JButton chooseButton = new JButton("随机产生");
this.add(label);
this.add(fileText);
this.add(chooseButton);
clickAction ca = new clickAction(this);
chooseButton.addActionListener(ca);
}
//返回生成的密码（48个字符长度）
public String getKey(){
JTextField jtf = (JTextField)this.getComponent(1);
return jtf.getText();
}
private class clickAction implements ActionListener{
clickAction(Component c){
cmpt = c;
}
public void actionPerformed(ActionEvent event){
try{
KeyGenerator kg = KeyGenerator.getInstance("DES");
kg.init(56);
Key ke = kg.generateKey();
byte[] bytK1 = ke.getEncoded();
ke = kg.generateKey();
byte[] bytK2 = ke.getEncoded();
ke = kg.generateKey();
byte[] bytK3 = ke.getEncoded();
JPanel jp = (JPanel)cmpt;
JTextField jtf = (JTextField)jp.getComponent(1);
jtf.setText(getByteStr(bytK1)+getByteStr(bytK2)+getByteStr(bytK3));
}catch(Exception e){
e.printStackTrace();
}
}
private String getByteStr(byte[] byt){
String strRet = "";
for(int i=0;iBYT.LENGTH;I++){
//System.out.println(byt[i]);
strRet += getHexValue((byt[i]240)/16);
strRet += getHexValue(byt[i]15);
}
return strRet;
}
private String getHexValue(int s){
String sRet=null;
switch (s){
case 0: sRet = "0";break;
case 1: sRet = "1";break;
case 2: sRet = "2";break;
case 3: sRet = "3";break;
case 4: sRet = "4";break;
case 5: sRet = "5";break;
case 6: sRet = "6";break;
case 7: sRet = "7";break;
case 8: sRet = "8";break;
case 9: sRet = "9";break;
case 10: sRet = "A";break;
case 11: sRet = "B";break;
case 12: sRet = "C";break;
case 13: sRet = "D";break;
case 14: sRet = "E";break;
case 15: sRet = "F";
}
return sRet;
}
private Component cmpt;
}
}