插入源代码：（以下代码只是我用来测试cnblogs推荐的客户端中添加源代码的方法，效果还是比在线差了点，内容请忽略！！！！！）

/*
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* and open the template in the editor.
*/
package com.silianbo;

/**
*
* @author silianbo
*/
import java.awt.AWTException;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.image.BufferedImage;
import java.awt.image.RescaleOp;
import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JToolBar;
import javax.swing.JWindow;
import javax.swing.filechooser.FileNameExtensionFilter;
import javax.swing.filechooser.FileSystemView;
public class ScreenShot {
public static void main(String[] args) {

  EventQueue.invokeLater(() -> {
      try {
          ScreenShotWindow ssw=new ScreenShotWindow();
          ssw.setVisible(true);
      } catch (AWTException e) {
      }
  });
}
}
/*
* 截图窗口
*/
class ScreenShotWindow extends JWindow
{
private int orgx, orgy, endx, endy;
    private BufferedImage image=null;
    private BufferedImage tempImage=null;
    private BufferedImage saveImage=null;

    private ToolsWindow tools=null;

public ScreenShotWindow() throws AWTException{
   //获取屏幕尺寸
   Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
   this.setBounds(0, 0, d.width, d.height);

   //截取屏幕
   Robot robot = new Robot();
   image = robot.createScreenCapture(new Rectangle(0, 0, d.width,d.height));

   this.addMouseListener(new MouseAdapter() {
    @Override
   public void mousePressed(MouseEvent e) {
    //鼠标松开时记录结束点坐标，并隐藏操作窗口
             orgx = e.getX();
             orgy = e.getY();

             if(tools!=null){
              tools.setVisible(false);
             }
   }
   @Override
   public void mouseReleased(MouseEvent e) {
    //鼠标松开时，显示操作窗口
    if(tools==null){
     tools=new ToolsWindow(ScreenShotWindow.this,e.getX(),e.getY());
    }else{
     tools.setLocation(e.getX(),e.getY());
    }
    tools.setVisible(true);
    tools.toFront();
   }
  });

   this.addMouseMotionListener(new MouseMotionAdapter() {

   @Override
   public void mouseDragged(MouseEvent e) {
    //鼠标拖动时，记录坐标并重绘窗口
                endx = e.getX();
                endy = e.getY();

                //临时图像，用于缓冲屏幕区域放置屏幕闪烁
                Image tempImage2=createImage(ScreenShotWindow.this.getWidth(),ScreenShotWindow.this.getHeight());
                Graphics g =tempImage2.getGraphics();
                g.drawImage(tempImage, 0, 0, null);
                int x = Math.min(orgx, endx);
                int y = Math.min(orgy, endy);
                int width = Math.abs(endx - orgx)+1;
                int height = Math.abs(endy - orgy)+1;
                // 加上1防止width或height0
                g.setColor(Color.BLUE);
                g.drawRect(x-1, y-1, width+1, height+1);
                //减1加1都了防止图片矩形框覆盖掉
                saveImage = image.getSubimage(x, y, width, height);
                g.drawImage(saveImage, x, y, null);

                ScreenShotWindow.this.getGraphics().drawImage(tempImage2,0,0,ScreenShotWindow.this);
   }
  });
}

    @Override
    public void paint(Graphics g) {
        RescaleOp ro = new RescaleOp(0.8f, 0, null);
        tempImage = ro.filter(image, null);
        g.drawImage(tempImage, 0, 0, this);
    }
    //保存图像到文件
public void saveImage() throws IOException {
  JFileChooser jfc=new JFileChooser();
  jfc.setDialogTitle("保存");

  //文件过滤器，用户过滤可选择文件
  FileNameExtensionFilter filter = new FileNameExtensionFilter("JPG", "jpg");
  jfc.setFileFilter(filter);

  //初始化一个默认文件（此文件会生成到桌面上）
  SimpleDateFormat sdf = new SimpleDateFormat("yyyymmddHHmmss");
     String fileName = sdf.format(new Date());
     File filePath = FileSystemView.getFileSystemView().getHomeDirectory();
     File defaultFile = new File(filePath + File.separator + fileName + ".jpg");
     jfc.setSelectedFile(defaultFile);

  int flag = jfc.showSaveDialog(this);
  if(flag==JFileChooser.APPROVE_OPTION){
   File file=jfc.getSelectedFile();
   String path=file.getPath();
   //检查文件后缀，放置用户忘记输入后缀或者输入不正确的后缀
   if(!(path.endsWith(".jpg")||path.endsWith(".JPG"))){
    path+=".jpg";
   }
   //写入文件
   ImageIO.write(saveImage,"jpg",new File(path));
   System.exit(0);
  }
}
}
/*
* 操作窗口
*/
class ToolsWindow extends JWindow
{
private final ScreenShotWindow parent;

public ToolsWindow(ScreenShotWindow parent,int x,int y) {
  this.parent=parent;
  this.init();
  this.setLocation(x, y);
  this.pack();
  this.setVisible(true);
}

private void init(){

  this.setLayout(new BorderLayout());
  JToolBar toolBar=new JToolBar("Java 截图");

  //保存按钮
  JButton saveButton=new JButton(new ImageIcon("images/save.gif"));
  saveButton.addActionListener((ActionEvent e) -> {
      try {
          parent.saveImage();
      } catch (IOException e1) {
          e1.printStackTrace();
      }
  });
  toolBar.add(saveButton);

  //关闭按钮
  JButton closeButton=new JButton(new ImageIcon("images/close.gif"));
  closeButton.addActionListener((ActionEvent e) -> {
      System.exit(0);
  });
  toolBar.add(closeButton);

  this.add(toolBar,BorderLayout.NORTH);
}
}