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
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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();} |
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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
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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(); }} |
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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(); }} |
感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！
原文链接：http://www.cnblogs.com/wing011203/archive/2013/05/03/3056535.html
