Java回顾之I/O
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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();
- }
- }
- 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();
- }
#p#
- 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();
- }
接下里，我们来看一些其他的常用操作
- 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
- 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
- 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
- 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();
- }
- }
- 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();
- }
原文链接：http://www.cnblogs.com/wing011203/archive/2013/05/03/3056535.html
名称栏目：Java回顾之I/O
标题链接：http://zsjierui.cn/article/coedpjp.html