IO操作
一、File类：
定义：文件描述符，用于描述在磁盘上的一个文件，或目录
File 类构造器：
二、io读取xxx.properties文件
public class PropDemo{ public vo test(){ Properties prop = new Properties(); //1.绝对路径 File file = new File("/users/kechunwang/BaiCe/config.properties"); prop.load(new FileInputStream(file)); //读取key的value Object obj = prop.get("driver"); obj.sout; //2.相对于resources目录的相对路径 Properties prop1 = new Properties(); prop1.load(PropDemo.getClassLoader().getResourceAsStream("db/config.properties")); Object obj1 = prop.get("driver"); obj1.sout; } }
三、FileReader读取文件标准写法：
public class FileReaderDemo { public static void main(String[] args) { FileReader reader = null; try{ //文件描述 File file = new File("test.log"); //定义文件取流 reader = new FileReader(file); //文件读取 char[] buf = new char[256]; int len = 0; while ((len = reader.read(buf)) != -1){ System.out.println("len:"+len); //String构造，注意边界 String val = new String(buf,0,len); System.out.println(val); } // 理解的读取过程 // // while (len != -1) { // // len = reader.read(buf); // // if (len != -1) { // // String val = new String(buf, 0, len); // // System.out.println(val); // // } // } }catch (FileNotFoundException fnfe){ fnfe.printStackTrace(); }catch (IOException ioe){ ioe.printStackTrace(); }finally { //关流 if (null != reader){ try { reader.close(); }catch (IOException ioe){ ioe.printStackTrace(); } } } } }
四、OutputStream
public class OutputStreamDemo { public static void main(String[] args) throws IOException { FileOutputStream outputStream = null; try{ //定位文件描述 File file = new File("test.log"); //实例化要写文件的基本类FileOutputStream outputStream = new FileOutputStream(file); String str = "hello world111"; //写数据 outputStream.write(str.getBytes()); }catch (FileNotFoundException ffe){ System.out.println("文件没有"); }catch (IOException ioe){ System.out.println("写入失败"); }finally { //关流，千万要记得关闭 try { if (null != outputStream){ outputStream.close(); } }catch (IOException e){ e.printStackTrace(); } outputStream.close(); } } }
五、InputStream
public class IPDemo01 { public static void main(String[] args) { File file = new File("test.log"); // try (FileInputStream ins = new FileInputStream(file)){ byte[] buf = new byte[512]; int len = 0; while ((len=ins.read(buf))!= -1){ String val = new String(buf,0,len); System.out.println(val); } }catch (IOException ex){ throw new IllegalStateException(ex); } } public void test01(){ File file = new File("test.log"); try (InputStream ins = new FileInputStream(file)){ byte[] buf = new byte[512]; int len = 0; while ((len = ins.read(buf))!= -1){ String val = new String(buf,0,len); System.out.println(val); } }catch (IOException ioe){ throw new IllegalStateException(ioe); } } }
六、常用方法：
@Test public void test1(){ File file = new File("test.log"); //是否可读 boolean canRead = file.canRead(); //是否可写 boolean canWrite = file.canWrite(); //是否可执行： boolean canExecute = file.canExecute(); //给文件赋值读权限 file.setReadable(true); //获取文件名字 String fileName = file.getName(); //获取绝对路径： File fileAbsouluteFile = file.getAbsoluteFile(); //返回String类型的绝对路径： String fileAbsolutePath = file.getAbsolutePath(); //返回父目录 String fileParent = file.getParent(); System.out.println("fileParent:"+fileParent); // File fileParentFile = file.getParentFile(); System.out.println("fileParentFile:"+fileParentFile); // String filePath = file.getPath(); System.out.println("filePath:"+filePath); //判断是否为文件 boolean isFiled = file.isFile(); //判断是否为目录 boolean isDirectoryd = file.isDirectory(); }
七、复制：
public class CopyFile { public static void main(String[] args) throws Exception { String src = "test.log"; String dst = "test1.log"; //读 BufferedReader bufferedReader = new BufferedReader(new FileReader(src)); String val = null; String data = ""; while ((val = bufferedReader.readLine()) != null){ data += val + "\n"; } //写 BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(dst)); bufferedWriter.write(data); bufferedWriter.flush(); } }
八、遍历本地一个目录下，找到后缀名是.log的，且占用空间最大的那个文件删除
@Test public void test1(){ File dir = new File("/user"); //找到目录下的文件： File[] files = dir.listFiles(); //定义最小文件大小 long maxFileSize = 0; //定义最小文件 File maxFile = null; //遍历循环 for (File file:files){ String fileName = file.getName(); //判断名字结尾 if (fileName.endsWith(".log")){ long len = file.length(); if (len > maxFileSize){ maxFileSize = len; maxFile = file; } } } maxFile.delete(); }
九、BufferedReader
public class BufferedReaderDemo2 { public static void main(String[] args) { //文件描述 File file = new File("test.log"); BufferedReader bufferedReader = null; //定义文件读取流 try { //相比FileReader的区别 bufferedReader = new BufferedReader(new FileReader(file)); } catch (FileNotFoundException e) { e.printStackTrace(); } //文件读取 String val = null; try { while ((val = bufferedReader.readLine()) != null){ System.out.println(val); } } catch (IOException e) { e.printStackTrace(); }finally { //关流 if (bufferedReader != null){ try { bufferedReader.close(); } catch (IOException e) { e.printStackTrace(); } } } } }
public class BufferedReaderDemo { public static void main(String[] args) { Reader reader = null; try { //文件描述 File file = new File("test.log"); //定义文件读取流 reader = new BufferedReader(new FileReader(file)); //读取文件 char[] buf = new char[256]; int len = 0; while ((len = reader.read(buf)) != -1){ String val = new String(buf,0,len); System.out.println("val:"+val); } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException ioe){ ioe.printStackTrace(); } finally { //关流 if (reader != null){ try { reader.close(); } catch (IOException e) { e.printStackTrace(); } } } } }
十、BufferedOutputStream
public class BufferedOutputStreamDemo { public static void main(String[] args) { BufferedOutputStream bufferedOutputStream = null; //定义文件描述，文件名称和路径 File file = new File("test2.log"); try { //定义文件写入流 bufferedOutputStream = new BufferedOutputStream(new FileOutputStream(file)); String wirete = "hello workd a "; bufferedOutputStream.write(wirete.getBytes()); }catch (FileNotFoundException fnfe){ fnfe.printStackTrace(); }catch (IOException ioe){ ioe.printStackTrace(); }finally { //关流 if (bufferedOutputStream != null){ try { bufferedOutputStream.close(); }catch (IOException ioe){ ioe.printStackTrace(); } } } } }
