Java文件操作实例浅析
Java文件操作实例浅析
1. 实例一：创建文件和目录
在java.io包中有一个专门用于文件操作的类File类。此类提供了文件很多操作，如创建文件、删除文件、创建目录、删除目录等方法。
import java.io.File;
import java.io.IOException;
public class FileOperation1
{
publicstatic void main(String[] args)
{
//TODO Auto-generated method stub
Filef1=new File("d:\\test"); //在d盘上创建一个名为test的文件夹
Filef2=new File("11.txt"); //在当前路径下创建一个名为11.txt的文件
Filef3=new File("d:\\file.txt"); //在绝对路径下创建file.txt文件
Filef4=new File("d:\\","1.txt"); //前一个参数代表父路径,后一个参数代表子路径
booleansuc0=false;
booleansuc1=false;
booleansuc2=false;
booleansuc3=false;
booleansuc4=false;
booleansuc5=false;
booleansuc6=false;
try
{
suc0=f1.mkdir();//创建目录
suc1=f2.createNewFile();//创建指定文件,创建成功返回true,否则,返回false
suc2=f3.createNewFile();
suc3=f4.createNewFile();
}
catch(IOException e)
{
e.printStackTrace();
}
System.out.println(f1.isDirectory());//打印出f1是否为目录
System.out.println(suc1); //打印文件f2创建是否成功
System.out.println(f2.exists());//打印出文件f2是否存在,结果是true或者false;
System.out.println(f3.getAbsolutePath());//打印出f3的绝对路径名
System.out.println(f3.getName());//打印出f3的文件名
System.out.println(f3.getParent());//打印出f3的父路径
System.out.println(f4.isFile());//打印出f3是否为文件
System.out.println(f4.length());//打印出f3的长度
Filef5=new File("e:\\test\\abc"); //在e盘test文件夹下创建文件夹abc,此时在e盘上有test文件夹,则文件夹 abc创建成功,否则创建失败
if(f5.exists())f5.delete();
suc4=f5.mkdir();//创建目录
System.out.println(suc4);
Filef6=new File("e:\\aa.txt");
if(f6.exists())f6.delete(); //如果文件f6以前存在,则删除
try
{
suc5=f6.createNewFile();
}
catch(IOExceptione)
{
e.printStackTrace();
}
System.out.println(suc5);
suc6=f6.setReadOnly();//将文件f7设置为只读
System.out.println(suc6);
}
}
2. 实例二：显示文件夹中所有文件，包括该文件夹中子文件夹的文件
importjava.io.BufferedReader;
importjava.io.File;
importjava.io.IOException;
importjava.io.InputStreamReader;
publicclass FileOperation2
{
private void ShowAllFiles(File file)
{
String name=file.getName();
System.out.println(name);
if(file.isDirectory())
{
File[] files=file.listFiles(); //获取该文件夹中所有文件
int i;
for(i=0;i<files.length;i++)
{
ShowAllFiles(files[i]); //递归,递归终止条件是//file.isDirectory()==false
}
}
}
public static void main(String[] args) throwsIOException
{
// TODO Auto-generated method stub
BufferedReader br=new BufferedReader(newInputStreamReader(System.in));
System.out.println("请输入一个路径:");
String path=br.readLine();
File dirFile=new File(path);
if(dirFile.isDirectory()==false)
{
System.out.println("输入的不是合法路径,此目录不存在!");
System.exit(1);
}
FileOperation2 fo=new FileOperation2();
fo.ShowAllFiles(dirFile);
}
}
3. 实例三：读取文件
方案一：
importjava.io.FileInputStream;
importjava.io.IOException;
publicclass FileOperation3
{
final static int max=1024*1024;
public static void main(String[] args) throwsIOException
{
// TODO Auto-generated method stub
FileInputStream fis=null; //定义一个文件输入流
try
{
fis=newFileInputStream("e:\\11.txt"); //创建文件输入流,数据源是e:\\11.doc
byte[] data=new byte[max];
int i=0;
while(fis.read()!=-1)//当读输入流达到末尾时,read()方法返回-1
{
data[i++]=(byte)fis.read();//read()每次从输入流读取一个字节
}
String str=new String(data,0,i); //解析读取的数据
System.out.println(str); //显示读取的结果
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
fis.close(); //关闭输入流
}
}
}
方案二：
importjava.io.FileInputStream;
importjava.io.IOException;
publicclass FileException4
{
finalstaticintmax=1024*1024;
publicstaticvoid main(String[]args) throws IOException
{
// TODO Auto-generatedmethod stub
FileInputStreamfis=null;
fis=new FileInputStream("d:\\1.txt");
byte [] buff=newbyte[max];
int len=0;
try
{
len=fis.read(buff);
Stringstr=new String(buff,0,len);
System.out.println(str);
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
fis.close();
}
}
}
方案三：
import java.io.FileInputStream;
importjava.io.FileReader;
importjava.io.IOException;
publicclass FileException5
{
finalstaticintmax=1024*1024;
publicstaticvoid main(String[]args) throws IOException
{
// TODO Auto-generatedmethod stub
FileReader fr=null;
fr=new FileReader("d:\\1.txt");
char [] buff=newchar[max];
int len=0;
try
{
len=fr.read(buff);
Stringstr=new String(buff,0,len);
System.out.println(str);
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
fr.close();
}
}
}
4. 实例四: 单线程下载程序
本实例共有4个类，分别是保存下载文件类、单线程下载类、单线程下载启动类和主界面类。
（1）保存下载文件类
import java.io.IOException;
import java.io.RandomAccessFile;
public class SaveDownloadFile //保存下载文件到本地随机文件类
{
privateRandomAccessFile localfile;
publicSaveDownloadFile()
{
localfile=null;
}
publicSaveDownloadFile(String filepath) throws IOException
{
localfile=newRandomAccessFile(filepath,"rw");
}
public void write(byte[] buff,intstart,int length) //可供多个线程使用的方法
{
try
{
this.localfile.write(buff,start, length);
}
catch(IOExceptione)
{
e.printStackTrace();
}
}
publicvoid close()
{
try
{
if(this.localfile!=null)this.localfile.close();
}
catch(Exceptione)
{
e.printStackTrace();
}
}
}
（2）单线程下载类
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
importorg.omg.CORBA.portable.InputStream;
public class SingleThreadDownloadextends Thread
//每个线程将下载的内容保存到本地随机访问文件中
{
privateString url; //URL
private String savefilepath; //保存为本地随机文件绝对路径
privateSaveDownloadFile sdf; //本地随机访问文件的对象
privatestatic URL url_obj;
privatestatic HttpURLConnection conn;
privatestatic java.io.InputStream is;
privatefinal static int buffsize=1024*1024;
//定义下载缓冲区大小
privatebyte[] buff; //下载的缓冲区
public SingleThreadDownload(Stringurl,String savefilepath)
{
super();
this.url=url;
this.savefilepath=savefilepath;
try
{
this.sdf=newSaveDownloadFile(savefilepath);
buff=newbyte[buffsize];
url_obj=newURL(this.url);
conn=(HttpURLConnection)url_obj.openConnection();
conn.setReadTimeout(10000);//设置读取数据超时
is=conn.getInputStream();
}
catch(Exceptione)
{
e.printStackTrace();
}
}
publicvoid run()
{
try
{
intlength=0;
while((length=is.read(buff))>0)
{
this.sdf.write(buff,0, length);
}
System.out.println("下载已经完成!");
}
catch(Exceptione)
{
e.printStackTrace();
}
finally
{
this.sdf.close();
try
{
is.close();
}
catch(Exception e)
{
//TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
（3）单线程下载启动类
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class SingleThreadDownloadStartimplements Runnable
{
privateString url;
privateString savefilepath; //下载文件保存的绝对路径
privateSingleThreadDownload std;
SingleThreadDownloadStart(Stringurl,String savefilepath)
{
this.url=url;
this.savefilepath=savefilepath;
this.std=new SingleThreadDownload(url,savefilepath);
}
publicvoid run()
{
//TODO Auto-generated method stub
this.std.start();
}
}
（4）主界面类
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
public class Mainclass //主类
{
privateString url; //下载的URL
privateString pathname; //下载文件要保存的本地路径,此路径可能包含文件名
privateString downloadfilename; //下载文件的名,从url抽取的文件名
privateString savefilename=null; //下载后保存的文件名
privateSingleThreadDownloadStart stds;
Mainclass(Stringurl,String pathname)
{
CheckURL(url);
CheckPathname(pathname);
this.stds=newSingleThreadDownloadStart(this.url,this.pathname);
this.stds.run();
}
voidCheckURL(String url)
{
intpos=url.lastIndexOf("/"); //获取字符"/"出现的最后一个位置
if(pos>=url.length()-1) //此时说明/后已经没有字符串了
{
System.out.println("URL不合法!");
System.exit(1);
}
else
{
this.downloadfilename=url.substring(pos+1,url.length()); //获取下载的文件名
if(this.downloadfilename.contains(".")==false)
{
System.out.println("URL不合法");
System.exit(1);
}
this.url=url;
}
}
voidCheckPathname(String pathname)
{
File[] roots=File.listRoots(); //获取Windows下所有盘符
if(pathname.contains("\\")==false)
{
System.out.println("要保存的路径不合法!");
System.exit(1);
}
int i;
booleanexist=false;
for(i=0;i<roots.length;i++)
{
Stringupper=roots[i].toString();
Stringlower=upper.toLowerCase();
if(pathname.contains(upper)==true|| pathname.contains(lower)==true) exist=true;
}
if(exist==false)
{
System.out.println("要保存的路径不合法!");
System.exit(1);
}
this.pathname=pathname;
i=pathname.lastIndexOf("\\");
if(i<pathname.length()-1) this.savefilename=pathname.substring(i+1, pathname.length());
else //pathname不包含文件名
{
this.savefilename=this.downloadfilename;
this.pathname+=this.savefilename;
}
}
finalpublic void Show()
{
System.out.println("下载文件名:"+this.downloadfilename);
System.out.println("保存的文件名:"+this.savefilename);
System.out.println("下载要保存的路径名:"+this.pathname);
}
publicstatic void main(String[] args) throws IOException
{
//TODO Auto-generated method stub
BufferedReaderbr=new BufferedReader(new InputStreamReader(System.in));
System.out.println("请输入URL=");
Stringurl=br.readLine();
System.out.println("请输入要下载文件的路径名:");
Stringpathname=br.readLine();
Mainclassmainclass=new Mainclass(url,pathname);
mainclass.Show();
}
}
5. 对象序列化实例：读取和保存对象
(1) 测试类A
importjava.io.Serializable;
publicclass TestClassA implements Serializable
{
privatestaticfinallongserialVersionID=11111111;
private TestClassB b;
publicfinal TestClassB get()
{
returnb;
}
publicvoid set(TestClassB b)
{
this.b=b;
}
}
(2) 测试类B
importjava.io.Serializable;
publicclass TestClassB implements Serializable
{
privatestaticfinallongserialVersionID=00000000;
private String str;
publicfinal String get()
{
returnstr;
}
publicvoid set(String str)
{
this.str=str;
}
}
(3) 序列化测试类
importjava.io.BufferedReader;
importjava.io.FileInputStream;
importjava.io.FileOutputStream;
importjava.io.InputStreamReader;
importjava.io.ObjectInputStream;
import java.io.ObjectOutputStream;
publicclass SerializeTest
{
publicvoid SaveObject(Objecto,String filepath)
{
FileOutputStreamfos=null; //定义文件输出流
ObjectOutputStreamos=null; //定义对象输出流
try
{
fos=newFileOutputStream(filepath);
os=new ObjectOutputStream(fos);
long StartTime=System.currentTimeMillis();
//获取系统当前时间
os.writeObject(o);
System.out.println("对象保存时间:"+(System.currentTimeMillis()-StartTime));
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
try
{
os.flush();
System.out.println("对象保存成功!");
os.close();
fos.close();
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
fos=null;
os=null;
}
}
}
publicfinal ObjectGetObject(String filepath)
{
FileInputStreamfis=null; //定义文件输入流
ObjectInputStreamis=null; //定义对象输入流
Objecto=null;
try
{
fis=newFileInputStream(filepath);
is=newObjectInputStream(fis);
long StartTime=System.currentTimeMillis();
//获取系统当前时间
o=is.readObject();
System.out.println("对象保存时间:"+(System.currentTimeMillis()-StartTime));
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
System.out.println("对象读取成功!");
try
{
is.close();
fis.close();
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
is=null;
fis=null;
}
}
return o;
}
publicstaticvoid main(String[]args)
{
TestClassAa=new TestClassA();
TestClassB b=new TestClassB();
b.set("HelloWorld, I am Wangzhicheng!");
a.set(b);
BufferedReaderbr=new BufferedReader(newInputStreamReader(System.in));
Stringfilepath=null;
try
{
filepath=br.readLine();
}
catch(Exception e)
{
e.printStackTrace();
}
SerializeTestst=new SerializeTest();
st.SaveObject(a,filepath);
TestClassAcopyA=(TestClassA)st.GetObject(filepath);
System.out.println(copyA.get().get());
}
}