java 基础知识之IO总结

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

FileInputStream：操作文件，经常和BufferedInputStream一起使用

PipedInputStream：可用于线程间通信

ObjectInputStream：可用于对象序列化

ByteArrayInputStream：用于处理字节数组的输入

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);

}

}

cVonmFjlatch(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;VonmFjl

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;

VonmFjl 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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