Java常用基础技术

java得到文件路径下的所有文件名 ] /* * @param 声明File对象,指定参数filePath */  File dir = new File(filePath); //返回此抽象路径下的文件  File[] files = dir.listFiles(); if (files == null) return;  for (int i = 0; i < files.length; i++) { //判断此文件是否是一个文件  if (！files[i].isDirectory()) { System.out.println(files[i].getName()); } }  -------------------------------- 1.创建文件: /**        * 上传文件        *         * @param file 上传文件实体        * @param filename 上传文件新命名        * @param dir  上传文件目录        * @return        */       public static boolean uploadFile(File file, String dir, String filename) {            boolean ret = false;            try {                if (file != null) {                    java.io.File filePath = new java.io.File(dir);                    if (!filePath.exists()) {                        filePath.mkdir();                    }                    String target = dir + filename;                    FileOutputStream outputStream = new FileOutputStream(target);                    FileInputStream fileIn = new FileInputStream(file);                    byte[] buffer = new byte[1024];                    int len;                    while ((len = fileIn.read(buffer)) > 0) {                        outputStream.write(buffer, 0, len);                    }                    fileIn.close();                    outputStream.close();                    ret = true;                }            } catch (Exception ex) {                log.info("上传文件无法处理，请确认上传文件！");            }            return ret;        }   --------------------------------- 删除文件: /**        * 删除文件        *         * @param filePathAndName 删除文件完整路径:d:/filedir/filename        * @return        */       public static boolean delFile(String filePathAndName) {            boolean ret = false;            try {                new File(filePathAndName.toString()).delete();                ret = true;               } catch (Exception e) {                System.out.println("删除文件操作出错");                e.printStackTrace();            }            return ret;        }   ---------------------------------------- 删除目录下全部文件: /**        * 删除目录下的文件        *         * @param dir 文件目录 d:/filedir/        * @return        */       public static boolean delFiles(String dir) {            boolean ret = false;            try {                File filePath = new File(dir);// 查询路径                String[] files = filePath.list();// 存放所有查询结果                int i = 0;                for (i = 0; i < files.length; i++) {                    new java.io.File(dir + "/" + files[i]).delete();                }                ret = true;            } catch (Exception e) {                e.printStackTrace();            }            return ret;        }   -------------------------------------------- .判断文件是否存在 /**        * 判断文件是否存在        *         * @param filename        * @return        */       public static boolean isExist(String filename) {            boolean ret = false;            try {                File file = new File(filename.toString());                if (file.exists()) {                    ret = true;                }            } catch (Exception e) {                e.printStackTrace();            }            return ret;        }   ------------------------------------------------- 根据制定路径，可以获取当前正在操作的文件的大小，容量为byte.  import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; public class FileByte { private String filePath = "D:\\m07012600030000001_z.wav"; private void getFileByte(){           File f = new File(filePath)   ;              try{                FileInputStream fis = new FileInputStream(f) ;                try   {                 System.out.println(fis.available())   ;                }catch(IOException e1){                e1.printStackTrace();                }                }catch(FileNotFoundException e2){                e2.printStackTrace();                }          } public static void main(String[] args) {     FileByte fb = new FileByte();     fb.getFileByte(); } } ------------------------------------------------------- 如何用java获取网络文件的大小(多线程 import java.io.BufferedInputStream; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; public class saveToFile { public void saveToFile(String destUrl, String fileName) throws IOException  {      FileOutputStream fos = null;      BufferedInputStream bis = null;      HttpURLConnection httpUrl = null;      URL url = null;      byte[] buf = new byte[2];      int size = 0;      int s=0;      //建立链接     url = new URL(destUrl);      httpUrl = (HttpURLConnection) url.openConnection();      //连接指定的资源      httpUrl.connect();      //获取网络输入流      bis = new BufferedInputStream(httpUrl.getInputStream());      //建立文件      fos = new FileOutputStream(fileName);       System.out.println("正在获取链接[" + destUrl + "]的内容...\n将其保存为文件[" + fileName + "]");      //保存文件      while ( (size = bis.read(buf)) != -1)       {      fos.write(buf, 0, size);      //++s;      System.out.println(size);      //System.out.println(s/1024+"M");      }              fos.close();      bis.close();      httpUrl.disconnect();    }    //多线程文件下载程序: public class DownloadNetTest {      private File fileOut;      private java.net.URL url;      private long fileLength=0;      //初始化线程数      private int ThreadNum=5;      public DownloadNetTest(){      try{         System.out.println("正在链接URL");         url=new URL("http://211.64.201.201/uploadfile/nyz.mp3");         HttpURLConnection urlcon=(HttpURLConnection)url.openConnection();         //根据响应获取文件大小        fileLength=urlcon.getContentLength();         if(urlcon.getResponseCode()>=400){         System.out.println("服务器响应错误");         System.exit(-1);         }         if(fileLength<=0)         System.out.println("无法获知文件大小");         //打印信息         printMIME(urlcon);         System.out.println("文件大小为"+fileLength/1024+"K");         //获取文件名         String trueurl=urlcon.getURL().toString();         String filename=trueurl.substring(trueurl.lastIndexOf('/')+1);         fileOut=new File("D://",filename);      }      catch(MalformedURLException e){         System.err.println(e);      }      catch(IOException e){         System.err.println(e);      }      init();  }      private void init(){         DownloadNetThread [] down=new DownloadNetThread[ThreadNum];      try {         for(int i=0;i<ThreadNum;i++){            RandomAccessFile randOut=new RandomAccessFile(fileOut,"rw");            randOut.setLength(fileLength);            long block=fileLength/ThreadNum+1;            randOut.seek(block*i);            down[i]=new DownloadNetThread(url,randOut,block,i+1);            down[i].setPriority(7);            down[i].start();         }      //循环判断是否下载完毕      boolean flag=true;      while (flag) {         Thread.sleep(500);         flag = false;         for (int i = 0; i < ThreadNum; i++)         if (!down[i].isFinished()) {         flag = true;         break;         }     }// end while      System.out.println("文件下载完毕，保存在"+fileOut.getPath() );     } catch (FileNotFoundException e) {            System.err.println(e);            e.printStackTrace();      }      catch(IOException e){         System.err.println(e);         e.printStackTrace();      }      catch (InterruptedException e) {      System.err.println(e);      }  }  private void printMIME(HttpURLConnection http){      for(int i=0;;i++){      String mine=http.getHeaderField(i);      if(mine==null)      return;      System.out.println(http.getHeaderFieldKey(i)+":"+mine);      }  }  //线程类 public class DownloadNetThread extends Thread{  private InputStream randIn;  private RandomAccessFile randOut;  private URL url;  private long block;  private int threadId=-1;  private boolean done=false;      public DownloadNetThread(URL url,RandomAccessFile out,long block,int threadId){      this.url=url;      this.randOut=out;      this.block=block;      this.threadId=threadId;  }    public void run(){      try{         HttpURLConnection http=(HttpURLConnection)url.openConnection();         http.setRequestProperty("Range","bytes="+block*(threadId-1)+"-");         randIn=http.getInputStream();      }      catch(IOException e){         System.err.println(e);      }      ////////////////////////      byte [] buffer=new byte[1024];      int offset=0;      long localSize=0;      System.out.println("线程"+threadId+"开始下载");      try {         while ((offset = randIn.read(buffer)) != -1&&localSize<=block) {         randOut.write(buffer,0,offset);         localSize+=offset;         }         randOut.close();         randIn.close();         done=true;         System.out.println("线程"+threadId+"完成下载");         this.interrupt();      }      catch(Exception e){         System.err.println(e);      }  }     public boolean isFinished(){        return done;     }  } } /*public static void main(String[] args) {          DownloadNetTest app=new DownloadNetTest();  } */ } ---------------------------- pom.xml里面声明java的jar  dependency>              <groupId>com.sun</groupId>              <artifactId>tools</artifactId>              <version>1.6.0< ersion>              <scope>system</scope>              <systemPath>C:/Program Files/Java k1.6.0_05 b/tools.jar</systemPath>       </dependency> ---------------------------------------------- 获取的路径里有空格变成20%以后，用什么把这个还原 String path = "111120%"; path=path.replace（"20%"," "）; 13795111413 ---------------------------------------- 70 到 110  之间怎么随机呢？   int ss=(int)(71+Math.random()*(100-71+1));     System.out.println(ss); ------------------------------------------ 使用Calendar 处理时间格式 public static long parse(String dstr) { if (dstr == null || dstr.length() == 0) { return 0; } if (NumberUtils.isNumber(dstr)) { return Long.parseLong(dstr) * 86400000; } String year = ""; String month = ""; String day = ""; int flag = 1; char prech = 0; dstr=dstr.trim(); for (char ch : dstr.toCharArray()) { if (ch <= '9' && ch >= '0') { switch (flag) { case 1: year += ch; break; case 2: month += ch; break; case 3: day += ch; break; } } else { if (prech <= '9' && prech >='0') flag++; } prech = ch; } int y = year.equals("") ? 1970 : Integer.parseInt(year); int m = month.equals("") ? 1 : Integer.parseInt(month); int d = day.equals("") ? 1 : Integer.parseInt(day); Calendar cal = Calendar.getInstance(); cal.set(Calendar.YEAR, y); cal.set(Calendar.MONTH, m-1); cal.set(Calendar.DAY_OF_MONTH, d); return cal.getTimeInMillis(); }  ------------------------------- 输出任何格式的时间 截取时间 public void InterceptionTime() {     //先制造一个完整的时间.     DateFormat allTimeFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");     Date allTime = null;     try {       allTime = allTimeFormat.parse("2009-06-05 10:12:24.577");     } catch (Exception e) {       // TODO Auto-generated catch block       e.printStackTrace();     }     //截取时间,也可以使用下边的SimpleDateFormat     DateFormat format = new SimpleDateFormat("HH:mm:ss.SSS");     String value = format.format(allTime);     System.out.println(value);          SimpleDateFormat  dateFormat = new SimpleDateFormat ("yyyy-MM-dd");     String value2=dateFormat.format(allTime);     System.out.println(value2);   } --------------------------------- 转换2进制， lang包中Integer类中有个static String toBinaryString(int i) ---------------------------------------------- oracle怎么判断表是否存在  select count(*) into num from USER_TABLES where TABLE_NAME='T2'  if num>0 then    --存在  end if; ------------------------------------------------------ 记住帐号和密码 JS   //   存cookie       Cookie   user   =   new   Cookie("User_Name",   "hsyd");       Cookie   pass   =   new   Cookie("Password",   "hsyd");       response.addCookie(user);       response.addCookie(pass);              //   取cookie       Cookie[]   cookies   =   request.getCookies();       //   ...找到匹配的cookie即可。