郑州java培训
郑州文化路中心

400-017-8985

热门课程

郑州java培训:这些java程序片段让你学java不难

  • 时间:2018-06-07 15:37
  • 发布:郑州达内
  • 来源:郑州java培训网

怎么样学java呢,为何都说java编程比较难呢?

其实学习java也是需要窍门的,如果你正在学习java的路上,那你还等什么呢,赶紧来看看20个非常有用的Java程序片段,好好的学习下java吧!郑州java培训班小编祝你在学习java的路上顺风顺水!

1. 字符串有整型的相互转换

String a = String.valueOf(2);   //integer to numeric string   int i = Integer.parseInt(a); //numeric string to an int

2. 向文件末尾添加内容

BufferedWriter out = null;   try {       out = new BufferedWriter(new FileWriter(”filename”, true));       out.write(”aString”);   } catch (IOException e) {       // error processing code   } finally {       if (out != null) {           out.close();       }   }

3. 得到当前方法的名字

String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();

4. 转字符串到日期

java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);

或者是:

SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );   Date date = format.parse( myString );

5. 使用JDBC链接Oracle

public class OracleJdbcTest   {       String driverClass = "oracle.jdbc.driver.OracleDriver";       Connection con;       public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException       {           Properties props = new Properties();           props.load(fs);           String url = props.getProperty("db.url");           String userName = props.getProperty("db.user");           String password = props.getProperty("db.password");           Class.forName(driverClass);           con=DriverManager.getConnection(url, userName, password);       }       public void fetch() throws SQLException, IOException       {           PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");           ResultSet rs = ps.executeQuery();           while (rs.next())           {               // do the thing you do           }           rs.close();           ps.close();       }       public static void main(String[] args)       {           OracleJdbcTest test = new OracleJdbcTest();           test.init();           test.fetch();       }   }

6. 把 Java util.Date 转成 sql.Date

java.util.Date utilDate = new java.util.Date();   java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());

7. 使用NIO进行快速的文件拷贝

public static void fileCopy( File in, File out )               throws IOException       {           FileChannel inChannel = new FileInputStream( in ).getChannel();           FileChannel outChannel = new FileOutputStream( out ).getChannel();           try          {   //          inChannel.transferTo(0, inChannel.size(), outChannel);      // original -- apparently has trouble copying large files on Windows               // magic number for Windows, 64Mb - 32Kb)               int maxCount = (64 * 1024 * 1024) - (32 * 1024);               long size = inChannel.size();               long position = 0;               while ( position < size )               {                  position += inChannel.transferTo( position, maxCount, outChannel );               }           }           finally          {               if ( inChannel != null )               {                  inChannel.close();               }               if ( outChannel != null )               {                   outChannel.close();               }           }       }

8. 创建图片的缩略图

private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)           throws InterruptedException, FileNotFoundException, IOException       {           // load image from filename           Image image = Toolkit.getDefaultToolkit().getImage(filename);           MediaTracker mediaTracker = new MediaTracker(new Container());           mediaTracker.addImage(image, 0);           mediaTracker.waitForID(0);           // use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny());           // determine thumbnail size from WIDTH and HEIGHT           double thumbRatio = (double)thumbWidth / (double)thumbHeight;           int imageWidth = image.getWidth(null);           int imageHeight = image.getHeight(null);           double imageRatio = (double)imageWidth / (double)imageHeight;           if (thumbRatio < imageRatio) {               thumbHeight = (int)(thumbWidth / imageRatio);           } else {               thumbWidth = (int)(thumbHeight * imageRatio);           }           // draw original image to thumbnail image object and           // scale it to the new size on-the-fly           BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);           Graphics2D graphics2D = thumbImage.createGraphics();           graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);           graphics2D.drawImage(image, 0, 0, thumbWidth, thumbHeight, null);           // save thumbnail image to outFilename           BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFilename));           JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);           JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);           quality = Math.max(0, Math.min(quality, 100));           param.setQuality((float)quality / 100.0f, false);           encoder.setJPEGEncodeParam(param);           encoder.encode(thumbImage);           out.close();       }

9. 创建 JSON 格式的数据

请先阅读这篇文章了解一些细节,

并下面这个JAR 文件:json-rpc-1.0.jar (75 kb)

import org.json.JSONObject;   ...   ...   JSONObject json = new JSONObject();   json.put("city", "Mumbai");   json.put("country", "India");   ...   String output = json.toString();   ...

10. 使用iText JAR生成PDF

阅读这篇文章了解更多细节

import java.io.File;   import java.io.FileOutputStream;   import java.io.OutputStream;   import java.util.Date;   import com.lowagie.text.Document;   import com.lowagie.text.Paragraph;   import com.lowagie.text.pdf.PdfWriter;   public class GeneratePDF {       public static void main(String[] args) {           try {               OutputStream file = new FileOutputStream(new File("C:\\Test.pdf"));               Document document = new Document();               PdfWriter.getInstance(document, file);               document.open();               document.add(new Paragraph("Hello Kiran"));               document.add(new Paragraph(new Date().toString()));               document.close();               file.close();           } catch (Exception e) {               e.printStackTrace();           }       }   }

11. HTTP 代理设置

阅读这篇 文章了解更多细节。

System.getProperties().put("http.proxyHost", "someProxyURL");   System.getProperties().put("http.proxyPort", "someProxyPort");   System.getProperties().put("http.proxyUser", "someUserName");   System.getProperties().put("http.proxyPassword", "somePassword");

12. 单实例Singleton 示例

请先阅读这篇文章了解更多信息

public class SimpleSingleton {       private static SimpleSingleton singleInstance =  new SimpleSingleton();       //Marking default constructor private       //to avoid direct instantiation.       private SimpleSingleton() {       }       //Get instance for class SimpleSingleton       public static SimpleSingleton getInstance() {           return singleInstance;       }   }

另一种实现

public enum SimpleSingleton {       INSTANCE;       public void doSomething() {       }   }   //Call the method from Singleton:   SimpleSingleton.INSTANCE.doSomething();

13. 抓屏程序

阅读这篇文章获得更多信息。

import java.awt.Dimension;   import java.awt.Rectangle;   import java.awt.Robot;   import java.awt.Toolkit;   import java.awt.image.BufferedImage;   import javax.imageio.ImageIO;   import java.io.File;   ...   public void captureScreen(String fileName) throws Exception {      Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();      Rectangle screenRectangle = new Rectangle(screenSize);      Robot robot = new Robot();      BufferedImage image = robot.createScreenCapture(screenRectangle);      ImageIO.write(image, "png", new File(fileName));   }   ...

14. 列出文件和目录

File dir = new File("directoryName");     String[] children = dir.list();     if (children == null) {         // Either dir does not exist or is not a directory     } else {         for (int i=0; i < children.length; i++) {             // Get filename of file or directory             String filename = children[i];         }     }     // It is also possible to filter the list of returned files.     // This example does not return any files that start with `.'.     FilenameFilter filter = new FilenameFilter() {         public boolean accept(File dir, String name) {             return !name.startsWith(".");         }     };     children = dir.list(filter);     // The list of files can also be retrieved as File objects     File[] files = dir.listFiles();     // This filter only returns directories     FileFilter fileFilter = new FileFilter() {         public boolean accept(File file) {             return file.isDirectory();         }     };     files = dir.listFiles(fileFilter);

15. 创建ZIP和JAR文件

import java.util.zip.*;   import java.io.*;   public class ZipIt {       public static void main(String args[]) throws IOException {           if (args.length < 2) {               System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");               System.exit(-1);           }           File zipFile = new File(args[0]);           if (zipFile.exists()) {               System.err.println("Zip file already exists, please try another");               System.exit(-2);           }           FileOutputStream fos = new FileOutputStream(zipFile);           ZipOutputStream zos = new ZipOutputStream(fos);           int bytesRead;           byte[] buffer = new byte[1024];           CRC32 crc = new CRC32();           for (int i=1, n=args.length; i < n; i++) {               String name = args[i];               File file = new File(name);               if (!file.exists()) {                   System.err.println("Skipping: " + name);                   continue;               }               BufferedInputStream bis = new BufferedInputStream(                   new FileInputStream(file));               crc.reset();               while ((bytesRead = bis.read(buffer)) != -1) {                   crc.update(buffer, 0, bytesRead);               }               bis.close();               // Reset to beginning of input stream               bis = new BufferedInputStream(                   new FileInputStream(file));               ZipEntry entry = new ZipEntry(name);               entry.setMethod(ZipEntry.STORED);               entry.setCompressedSize(file.length());               entry.setSize(file.length());               entry.setCrc(crc.getValue());               zos.putNextEntry(entry);               while ((bytesRead = bis.read(buffer)) != -1) {                   zos.write(buffer, 0, bytesRead);               }               bis.close();           }           zos.close();       }   }

16. 解析/读取XML 文件

XML文件

<?xml version="1.0"?>  <students>      <student>          <name>John</name>          <grade>B</grade>          <age>12</age>      </student>      <student>          <name>Mary</name>          <grade>A</grade>          <age>11</age>      </student>      <student>          <name>Simon</name>          <grade>A</grade>          <age>18</age>      </student>  </students>

Java代码

package net.viralpatel.java.xmlparser;   import java.io.File;   import javax.xml.parsers.DocumentBuilder;   import javax.xml.parsers.DocumentBuilderFactory;   import org.w3c.dom.Document;   import org.w3c.dom.Element;   import org.w3c.dom.Node;   import org.w3c.dom.NodeList;   public class XMLParser {       public void getAllUserNames(String fileName) {           try {               DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();               DocumentBuilder db = dbf.newDocumentBuilder();               File file = new File(fileName);               if (file.exists()) {                   Document doc = db.parse(file);                   Element docEle = doc.getDocumentElement();                   // Print root element of the document                   System.out.println("Root element of the document: "                          + docEle.getNodeName());                   NodeList studentList = docEle.getElementsByTagName("student");                   // Print total student elements in document                   System.out                           .println("Total students: " + studentList.getLength());                   if (studentList != null && studentList.getLength() > 0) {                       for (int i = 0; i < studentList.getLength(); i++) {                           Node node = studentList.item(i);                           if (node.getNodeType() == Node.ELEMENT_NODE) {                               System.out                                       .println("=====================");                               Element e = (Element) node;                               NodeList nodeList = e.getElementsByTagName("name");                               System.out.println("Name: "                                      + nodeList.item(0).getChildNodes().item(0)                                               .getNodeValue());                               nodeList = e.getElementsByTagName("grade");                               System.out.println("Grade: "                                      + nodeList.item(0).getChildNodes().item(0)                                               .getNodeValue());                               nodeList = e.getElementsByTagName("age");                               System.out.println("Age: "                                      + nodeList.item(0).getChildNodes().item(0)                                               .getNodeValue());                           }                       }                   } else {                       System.exit(1);                   }               }           } catch (Exception e) {               System.out.println(e);           }       }       public static void main(String[] args) {           XMLParser parser = new XMLParser();           parser.getAllUserNames("c:\\test.xml");       }   }

17. 把 Array 转换成 Map

import java.util.Map;   import org.apache.commons.lang.ArrayUtils;   public class Main {     public static void main(String[] args) {       String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },           { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };       Map countryCapitals = ArrayUtils.toMap(countries);       System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));       System.out.println("Capital of France is " + countryCapitals.get("France"));     }   }

18. 发送邮件

import javax.mail.*;   import javax.mail.internet.*;   import java.util.*;   public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException   {       boolean debug = false;        //Set the host smtp address        Properties props = new Properties();        props.put("mail.smtp.host", "smtp.example.com");       // create some properties and get the default Session       Session session = Session.getDefaultInstance(props, null);       session.setDebug(debug);       // create a message       Message msg = new MimeMessage(session);       // set the from and to address       InternetAddress addressFrom = new InternetAddress(from);       msg.setFrom(addressFrom);       InternetAddress[] addressTo = new InternetAddress[recipients.length];       for (int i = 0; i < recipients.length; i++)       {           addressTo[i] = new InternetAddress(recipients[i]);       }       msg.setRecipients(Message.RecipientType.TO, addressTo);       // Optional : You can also set your custom headers in the Email if you Want       msg.addHeader("MyHeaderName", "myHeaderValue");       // Setting the Subject and Content Type       msg.setSubject(subject);       msg.setContent(message, "text/plain");       Transport.send(msg);   }

19. 发送代数据的HTTP 请求

import java.io.BufferedReader;   import java.io.InputStreamReader;   import java.net.URL;   public class Main {       public static void main(String[] args)  {           try {               URL my_url = new URL("http://coolshell.cn/");               BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));               String strTemp = "";               while(null != (strTemp = br.readLine())){               System.out.println(strTemp);           }           } catch (Exception ex) {               ex.printStackTrace();           }       }   }

20. 改变数组的大小

/**  * Reallocates an array with a new size, and copies the contents  * of the old array to the new array.  * @param oldArray  the old array, to be reallocated.  * @param newSize   the new array size.  * @return          A new array with the same contents.  */  private static Object resizeArray (Object oldArray, int newSize) {      int oldSize = java.lang.reflect.Array.getLength(oldArray);      Class elementType = oldArray.getClass().getComponentType();      Object newArray = java.lang.reflect.Array.newInstance(            elementType,newSize);      int preserveLength = Math.min(oldSize,newSize);      if (preserveLength > 0)         System.arraycopy (oldArray,0,newArray,0,preserveLength);      return newArray;   }   // Test routine for resizeArray().   public static void main (String[] args) {      int[] a = {1,2,3};      a = (int[])resizeArray(a,5);      a[3] = 4;      a[4] = 5;      for (int i=0; i<a.length; i++)         System.out.println (a[i]);   }
21.java操作excel
工具类:

package com.xxxxx.cnnvd.util;

import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.util.ArrayList; import java.util.Iterator;

import org.apache.poi.hssf.usermodel.HSSFCell; import org.apache.poi.hssf.usermodel.HSSFRow; import org.apache.poi.hssf.usermodel.HSSFSheet; import org.apache.poi.hssf.usermodel.HSSFWorkbook; import org.apache.poi.poifs.filesystem.POIFSFileSystem; import org.apache.poi.xssf.usermodel.XSSFCell; import org.apache.poi.xssf.usermodel.XSSFRow; import org.apache.poi.xssf.usermodel.XSSFSheet; import org.apache.poi.xssf.usermodel.XSSFWorkbook;

public class ReadExcelTool {    public ArrayList<ArrayList<String>> readExcel(String fileName,String path) {   ArrayList<ArrayList<String>> Row =new ArrayList<ArrayList<String>>();   try {        FileInputStream fileIn = new FileInputStream(new File(path,fileName));             POIFSFileSystem fs = new POIFSFileSystem(fileIn);             HSSFWorkbook wb = new HSSFWorkbook(fs);        for (int numSheet = 0; numSheet < wb.getNumberOfSheets(); numSheet++) {     HSSFSheet xssfSheet = wb.getSheetAt(numSheet);     if (xssfSheet == null) {      continue;     }     // 循环行Row     for (int rowNum = 1; rowNum <= xssfSheet.getLastRowNum(); rowNum++) {      HSSFRow xssfRow = xssfSheet.getRow(rowNum);      if (xssfRow == null) {       continue;      }            // 循环列Cell      ArrayList<String> cell =new ArrayList<String>();      for (int cellNum = 0; cellNum <= xssfRow.getLastCellNum(); cellNum++) {       HSSFCell xssfCell = xssfRow.getCell(cellNum);       if (xssfCell == null) {        continue;       }       cell.add(getValue(xssfCell));      }      Row.add(cell);     }    }   } catch (IOException e) {    e.printStackTrace();   }     return Row;  }

private String getValue(HSSFCell xssfCell) {   if (xssfCell.getCellType() == xssfCell.CELL_TYPE_BOOLEAN) {    return String.valueOf(xssfCell.getBooleanCellValue());   } else if (xssfCell.getCellType() == xssfCell.CELL_TYPE_NUMERIC) {    return String.valueOf(xssfCell.getNumericCellValue());   } else {    return String.valueOf(xssfCell.getStringCellValue());   }  }    /**

//测试类  public static void main(String[] args) {   ReadExcelTool ret = new ReadExcelTool();   ArrayList<ArrayList<String>> datas = ret.readExcel(“template.xls”, “D:\\java\\tomcat60\\webapps\\zyst\\impfiles”);   for (Iterator iterator = datas.iterator(); iterator.hasNext();) {    ArrayList<String> datas2 = (ArrayList<String>) iterator.next();    for (Iterator iterator2 = datas2.iterator(); iterator2.hasNext();) {     String name = (String) iterator2.next();     System.out.print(name);    }    System.out.println();       }  }  **/   }

使用工具类

/**   * 检查文件的后缀名称是否xls   *   * @param fileFileName2   * @return 返回文件后缀名xls,若不符合则返回null   */  private String checkSuffix(String fileFileName2) {   if (fileFileName2 == null) {    return null;   }   String fileName = fileFileName2.substring(fileFileName2.lastIndexOf(“.”) + 1);   if (fileName.equals(“xls”)) {    return “xls”;   }   return null;  }

/**   * 把excel数据导入数据库   *   * @return   */  public String cnnvdImportSave() {   String path = sRequest.getSession().getServletContext().getRealPath(“/uploadfiles”);  // System.out.println(path);   //必须是符合格式的excel文件   if (“xls”.equals(checkSuffix(fileFileName))) {    //路径    // ServletActionContext.getServletContext().getRealPath(“/”);    File savefile = new File(new File(path), fileFileName);    if (!savefile.getParentFile().exists()) {     savefile.getParentFile().mkdirs();    }    try {     FileUtils.copyFile(file, savefile);    } catch (IOException e) {     // TODO Auto-generated catch block     e.printStackTrace();    }    //读取excel文件    ReadExcelTool ret = new ReadExcelTool();    ArrayList<ArrayList<String>> datas = ret.readExcel(fileFileName, path);    //    SimpleDateFormat sdf = new SimpleDateFormat(“yyyy-MM-dd”);    if (datas != null && datas.size() > 0) {     for (int i = 0; i < datas.size(); i++) {      List temp = datas.get(i);      if (temp != null && temp.size() > 0) {        String vulname = (String) temp.get(3);        String levelid = (String) temp.get(30);        String vultype = (String) temp.get(39);        String vulpubtime = (String) temp.get(13);        String vulreptime = (String) temp.get(14);        Date vulpubtimeDate = null;        Date vulreptimeDate = null;        try {         vulpubtimeDate = sdf.parse(vulpubtime);         vulreptimeDate = sdf.parse(vulreptime);        } catch (ParseException e) {         // TODO Auto-generated catch block         e.printStackTrace();        }        String vulorg = (String) temp.get(40);        String vulsummary = (String) temp.get(4);        String pub = (String) temp.get(55);        String refurl = (String) temp.get(19);        String cnnvdid = (String) temp.get(1);        String cveid = (String) temp.get(9);        String bid = (String) temp.get(10);        //通过cnnvdid判断该条数据是否已存在,存在就先删除,再新增        if (vulnerabilityService.checkCnnvdIdExist(cnnvdid) != null) {         String sql4delete = “delete from t_cnnvd_vulnerability where cnnvdid = ?”;         jdbcTemplate.update(sql4delete,cnnvdid);        }        String sql = “insert into t_cnnvd_xxxxxxx(vulname,levelid,vultype,vulpubtime,vulreptime,vulorg,vulsummary,pub,refurl,cnnvdid,cveid,bid) values(?,?,?,?,?,?,?,?,?,?,?,?)”;        jdbcTemplate.update(sql,vulname,levelid,vultype,vulpubtime,vulreptime,vulorg,vulsummary,pub,refurl,cnnvdid,cveid,bid);      }     }    }    //把生成的临时文件删除    savefile.delete();    request.put(“cnnvdImportResult”, “success”);    return SUCCESS;    }   return ERROR;  }

22.java操作csv,使用CsvReader,需要下载使用javacsv.jar

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;
import org.apache.log4j.Logger;
import com.csvreader.CsvReader;
import com.csvreader.CsvWriter;
/**
* CSV测试类
*
*/
public class CSVTest {
protected static Logger logger = Logger.getLogger(CSVTest.class); /**
* 读取CSV文件
* @param file
* @return
*/
public static List<String[]> readCsv(String file) {
List<String[]> list = new ArrayList<String[]>();
CsvReader reader = null;
try {
// 初始化CsvReader并指定列分隔符和字符编码
reader = new CsvReader(file, ‘,’, Charset.forName(“GBK”));
while (reader.readRecord()) {
// 读取每行数据以数组形式返回
String[] str = reader.getValues();
if (str != null && str.length > 0) {

//reader.getCurrentRecord()得到当前记录的行号,第一行是头,不使用                     if ((reader.getCurrentRecord() != 0) && (str != null) && (str.length > 0)) {                         System.out.println(str.length);                         System.out.println(str[1]);                         list.add(str);                     }                 }             }         } catch (FileNotFoundException e) {             logger.error(e.getMessage(), e);         } catch (IOException e) {             logger.error(e.getMessage(), e);         } finally {             if (reader != null) {                 reader.close();             }         }         return list;     }

/**   * 写入CSV文件   */  public static void writeCsv(List<String[]> content, String path) {  CsvWriter writer = null;  try {  writer = new CsvWriter(path, ‘,’, Charset.forName(“GBK”));  if(content != null && content.size() != 0) {  for(String[] strArray : content) {  writer.writeRecord(strArray);  }  } else {  // 做异常处理  }  } catch (IOException e) {  logger.error(e.getMessage(), e);  } finally {  if(writer != null) {  writer.close(); }  }  }

/**   * @param args   * @throws Exception   */  public static void main(String[] args) throws Exception {  String readPath = “F:” + File.separator + “test” + File.separator + “muti-test.csv”; String writePath = “F:” + File.separator + “test” + File.separator + “muti-test-output.csv”;  List<String[]> result = readCsv(readPath);  for(String[] strArray : result) {  for(String s : strArray) {  System.out.print(s + “,”);  }  System.out.println();  }  writeCsv(result, writePath);  Thread.sleep(999999);  } }

整理了这些多,你能学的完吗,你能看的懂吗,如果自学java编程的路上遇到了坎,可别忘记了郑州java培训机构哦,这里等你来选择,等你来报名,毕竟学习java的路上有人陪才能学得快!

上一篇:郑州java培训:Java入门知识点全在这里了
下一篇:没有下一篇了

郑州java培训:Java入门知识点全在这里了

选择城市和中心
贵州省

广西省

海南省