java 基础知识之IO总结

java  基础知识之io总结

　    我计划在接下来的几篇文章中快速回顾一下java，主要是一些基础的jdk相关的内容。

　　工作后，使用的技术随着项目的变化而变化，时而c#，时而java，当然还有其他一些零碎的技术。总体而言，c#的使用时间要更长一些，其次是java。我本身对语言没有什么倾向性，能干活的语言，就是好语言。而且从面向对象的角度来看，我觉得c#和java对我来说，没什么区别。

　　这篇文章主要回顾java中和i/o操作相关的内容，i/o也是编程语言的一个基础特性，java中的i/o分为两种类型，一种是顺序读取，一种是随机读取。

　　我们先来看顺序读取，有两种方式可以进行顺序读取，一种是inputstream/outputstream，它是针对字节进行操作的输入输出流；另外一种是reader/writer，它是针对字符进行操作的输入输出流。

　　下面我们画出inputstream的结构

　　

1. fileinputstream：操作文件，经常和bufferedinputstream一起使用
2. pipedinputstream：可用于线程间通信
3. objectinputstream：可用于对象序列化
4. bytearrayinputstream：用于处理字节数组的输入
5. linenumberinputstream：可输出当前行数，并且可以在程序中进行修改
   

　　下面是outputstream的结构

　　

printstream：提供了类似print和println的接口去输出数据

　　下面我们来看如何使用stream的方式来操作输入输出

使用inputstream读取文件

使用fileinputstream读取文件信息
public static byte[] readfilebyfileinputstream(file file) throws ioexception
{
  bytearrayoutputstream output = new bytearrayoutputstream();
  fileinputstream fis = null;
  try
  {
    fis = new fileinputstream(file);
    byte[] buffer = new byte[1024];
    int bytesread = 0;
    while((bytesread = fis.read(buffer, 0, buffer.length)) != -1)
    {
      output.write(buffer, 0, bytesread);
    }
  }
  catch(exception ex)
  {
    system.out.println("error occurs during reading " + file.getabsolutefile());
  }
  finally
  {
    if (fis !=null) fis.close();
    if (output !=null) output.close();
  }
  return output.tobytearray();
}

使用bufferedinputstream读取文件
public static byte[] readfilebybufferedinputstream(file file) throws exception
{
  fileinputstream fis = null;
  bufferedinputstream bis = null;
  bytearrayoutputstream output = new bytearrayoutputstream();
  try
  {
    fis = new fileinputstream(file);
    bis = new bufferedinputstream(fis);
    byte[] buffer = new byte[1024];
    int bytesread = 0;
    while((bytesread = bis.read(buffer, 0, buffer.length)) != -1)
    {
      output.write(buffer, 0, bytesread);
    }
  }
  catch(exception ex)
  {
    system.out.println("error occurs during reading " + file.getabsolutefile());
  }
  finally
  {
    if (fis != null) fis.close();
    if (bis != null) bis.close();
    if (output != null) output.close();
  }
  return output.tobytearray();
}

使用outputstream复制文件

使用fileoutputstream复制文件
public static void copyfilebyfileoutputstream(file file) throws ioexception
{
  fileinputstream fis = null;
  fileoutputstream fos = null;
  try
  {
    fis = new fileinputstream(file);
    fos = new fileoutputstream(file.getname() + ".bak");
    byte[] buffer = new byte[1024];
    int bytesread = 0;
    while((bytesread = fis.read(buffer,0,buffer.length)) != -1)
    {
      fos.write(buffer, 0, bytesread);
    }
    fos.flush();
  }
  catch(exception ex)
  {
    system.out.println("error occurs during copying " + file.getabsolutefile());
  }
  finally
  {
    if (fis != null) fis.close();
    if (fos != null) fos.close();
  }
}

使用bufferedoutputstream复制文件
public static void copyfilebybufferedoutputstream(file file)throws ioexception
{
  fileinputstream fis = null;
  bufferedinputstream bis = null;
  fileoutputstream fos = null;
  bufferedoutputstream bos = null;
  try
  {
    fis = new fileinputstream(file);
    bis = new bufferedinputstream(fis);
    fos = new fileoutputstream(file.getname() + ".bak");
    bos = new bufferedoutputstream(fos);
    byte[] buffer = new byte[1024];
    int bytesread = 0;
    while((bytesread = bis.read(buffer, 0, buffer.length)) != -1)
    {
      bos.write(buffer, 0, bytesread);
    }
    bos.flush();
  }
  catch(exception ex)
  {
    system.out.println("error occurs during copying " + file.getabsolutefile());
  }
  finally
  {
    if (fis != null) fis.close();
    if (bis != null) bis.close();
    if (fos != null) fos.close();
    if (bos != null) bos.close();
  }
}

这里的代码对异常的处理非常不完整，稍后我们会给出完整严谨的代码。

　　下面我们来看reader的结构

　　

　　这里的reader基本上和inputstream能够对应上。　　

　　writer的结构如下

　　

　　下面我们来看一些使用reader或者writer的例子

使用reader读取文件内容

使用bufferedreader读取文件内容
public static string readfile(string file)throws ioexception
{
  bufferedreader br = null;
  stringbuffer sb = new stringbuffer();
  try
  {
    br = new bufferedreader(new filereader(file));
    string line = null;
    
    while((line = br.readline()) != null)
    {
      sb.append(line);
    }
  }
  catch(exception ex)
  {
    system.out.println("error occurs during reading " + file);
  }
  finally
  {
    if (br != null) br.close();
  }
  return sb.tostring();
}

使用writer复制文件

使用bufferedwriter复制文件
public static void copyfile(string file) throws ioexception
{ 
  bufferedreader br = null;
  bufferedwriter bw = null;
  try
  {
    br = new bufferedreader(new filereader(file));
    bw = new bufferedwriter(new filewriter(file + ".bak"));
    string line = null;
    while((line = br.readline())!= null)
    {
      bw.write(line);
    }
  }
  catch(exception ex)
  {
    system.out.println("error occurs during copying " + file);
  }
  finally
  {
    if (br != null) br.close();
    if (bw != null) bw.close();
  }
}

　　下面我们来看如何对文件进行随机访问，java中主要使用randomaccessfile来对文件进行随机操作。

创建一个大小固定的文件

创建大小固定的文件
public static void createfile(string file, int size) throws ioexception
{
  file temp = new file(file);
  randomaccessfile raf = new randomaccessfile(temp, "rw");
  raf.setlength(size);
  raf.close();
}

向文件中随机写入数据

向文件中随机插入数据
public static void writefile(string file, byte[] content, int startpos, int contentlength) throws ioexception
{
  randomaccessfile raf = new randomaccessfile(new file(file), "rw");
  raf.seek(startpos);
  raf.write(content, 0, contentlength);
  raf.close();
}

　　接下里，我们来看一些其他的常用操作

移动文件

移动文件
public static boolean movefile(string sourcefile, string destfile)
{
  file source = new file(sourcefile);
  if (!source.exists()) throw new runtimeexception("source file does not exist.");
  file dest = new file(destfile);
  if (!(new file(dest.getpath()).exists())) new file(dest.getparent()).mkdirs();
  return source.renameto(dest);
}

复制文件

复制文件
public static void copyfile(string sourcefile, string destfile) throws ioexception
{
  file source = new file(sourcefile);
  if (!source.exists()) throw new runtimeexception("file does not exist.");
  if (!source.isfile()) throw new runtimeexception("it is not file.");
  if (!source.canread()) throw new runtimeexception("file cound not be read.");
  file dest = new file(destfile);
  if (dest.exists())
  {
    if (dest.isdirectory()) throw new runtimeexception("destination is a folder.");
    else
    {
      dest.delete();
    }
  }
  else
  {
    file parentfolder = new file(dest.getparent());
    if (!parentfolder.exists()) parentfolder.mkdirs();
    if (!parentfolder.canwrite()) throw new runtimeexception("destination can not be written.");
  }
  fileinputstream fis = null;
  fileoutputstream fos = null;
  try
  {
    fis = new fileinputstream(source);
    fos = new fileoutputstream(dest);
    byte[] buffer = new byte[1024];
    int bytesread = 0;
    while((bytesread = fis.read(buffer, 0, buffer.length)) != -1)
    {
      fos.write(buffer, 0, bytesread);
    }
    fos.flush();
  }
  catch(ioexception ex)
  {
    system.out.println("error occurs during copying " + sourcefile);
  }
  finally
  {
    if (fis != null) fis.close();
    if (fos != null) fos.close();
  }
}

复制文件夹

复制文件夹
public static void copydir(string sourcedir, string destdir) throws ioexception
{
  
  file source = new file(sourcedir);
  if (!source.exists()) throw new runtimeexception("source does not exist.");
  if (!source.canread()) throw new runtimeexception("source could not be read.");
  file dest = new file(destdir);
  if (!dest.exists()) dest.mkdirs();
  
  file[] arrfiles = source.listfiles();
  for(int i = 0; i < arrfiles.length; i++)
  {
    if (arrfiles[i].isfile())
    {
      bufferedreader reader = new bufferedreader(new filereader(arrfiles[i]));
      bufferedwriter writer = new bufferedwriter(new filewriter(destdir + "/" + arrfiles[i].getname()));
      string line = null;
      while((line = reader.readline()) != null) writer.write(line);
      writer.flush();
      reader.close();
      writer.close();
    }
    else
    {
      copydir(sourcedir + "/" + arrfiles[i].getname(), destdir + "/" + arrfiles[i].getname());
    }
  }
}

删除文件夹

删除文件夹
public static void del(string filepath)
{
  file file = new file(filepath);
  if (file == null || !file.exists()) return;
  if (file.isfile())
  {
    file.delete();
  }
  else
  {
    file[] arrfiles = file.listfiles();
    if (arrfiles.length > 0)
    {
      for(int i = 0; i < arrfiles.length; i++)
      {
        del(arrfiles[i].getabsolutepath());
      }
    }
    file.delete();
  }
}

获取文件夹大小

获取文件夹大小
public static long getfoldersize(string dir)
{
  long size = 0;
  file file = new file(dir);
  if (!file.exists()) throw new runtimeexception("dir does not exist.");
  if (file.isfile()) return file.length();
  else
  {
    string[] arrfilename = file.list();
    for (int i = 0; i < arrfilename.length; i++)
    {
      size += getfoldersize(dir + "/" + arrfilename[i]);
    }
  }
  
  return size;
}

将大文件切分为多个小文件

将大文件切分成多个小文件
public static void splitfile(string filepath, long unit) throws ioexception
{
  file file = new file(filepath);
  if (!file.exists()) throw new runtimeexception("file does not exist.");
  long size = file.length();
  if (unit >= size) return;
  int count = size % unit == 0 ? (int)(size/unit) : (int)(size/unit) + 1;
  string newfile = null;
  fileoutputstream fos = null;
  fileinputstream fis =null;
  byte[] buffer = new byte[(int)unit];
  fis = new fileinputstream(file);
  long startpos = 0;
  string countfile = filepath + "_count";
  printwriter writer = new printwriter(new filewriter( new file(countfile)));
  writer.println(filepath + "\t" + size);
  for (int i = 1; i <= count; i++)
  {
    newfile = filepath + "_" + i;
    startpos = (i - 1) * unit;
    system.out.println("creating " + newfile);
    fos = new fileoutputstream(new file(newfile));
    int bytesread = fis.read(buffer, 0, buffer.length);
    if (bytesread != -1)
    {
      fos.write(buffer, 0, bytesread);
      writer.println(newfile + "\t" + startpos + "\t" + bytesread);
    }
    fos.flush();
    fos.close();
    system.out.println("startpos:" + i*unit + "; endpos:" + (i*unit + bytesread));
  }
  writer.flush();
  writer.close();
  fis.close();
}

将多个小文件合并为一个大文件

将多个小文件合并成一个大文件
public static void linkfiles(string countfile) throws ioexception
{
  file file = new file(countfile);
  if (!file.exists()) throw new runtimeexception("count file does not exist.");
  bufferedreader reader = new bufferedreader(new filereader(file));
  string line = reader.readline();
  string newfile = line.split("\t")[0];
  long size = long.parselong(line.split("\t")[1]);
  randomaccessfile raf = new randomaccessfile(newfile, "rw");
  raf.setlength(size);
  fileinputstream fis = null;
  byte[] buffer = null;
  
  while((line = reader.readline()) != null)
  {
    string[] arrinfo = line.split("\t");
    fis = new fileinputstream(new file(arrinfo[0]));
    buffer = new byte[integer.parseint(arrinfo[2])];
    long startpos = long.parselong(arrinfo[1]);
    fis.read(buffer, 0, integer.parseint(arrinfo[2]));
    raf.seek(startpos);
    raf.write(buffer, 0, integer.parseint(arrinfo[2]));
    fis.close();
  }
  raf.close();
}

执行外部命令

执行外部命令
public static void execexternalcommand(string command, string argument)
{
  process process = null;
  try
  {
    process = runtime.getruntime().exec(command + " " + argument);
    inputstream is = process.getinputstream();
    bufferedreader br = new bufferedreader(new inputstreamreader(is));
    string line = null;
    while((line = br.readline()) != null)
    {
      system.out.println(line);
    }
  }
  catch(exception ex)
  {
    system.err.println(ex.getmessage());
  }
  finally
  {
    if (process != null) process.destroy();
  }
}

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