Template

模板模式：定义一个操作的骨架。把一些其它操作延迟到子类中（例子：servlet中sevkce方法中定义了[doPost(),doGet(),doPut(),doDelete(),doTrace(),doHead()]）

 比如：

/**
 *  An abstract class which can get content from a file or a HTTP URL
 *  or other resource
 */
public abstract class AbstractRead {
    protected String resource;
    public void getContent() { // Template Method
        if(open()) {
            readContent();
            close();
        }
    }
    public void setResource(String s) {
        resource = s;
    }
    protected abstract boolean open();
    protected abstract void readContent();
    protected abstract void close();
//定义一个算法的骨架。把一些操作在子类中
}

/**
 *  A concrete class extends AbstractRead
 *  This class can read from a file
 */
import java.io.*;

public class ReadFile extends AbstractRead {
    private BufferedReader in = null;
    public ReadFile() {
    }
    public ReadFile(String fileName) {
        resource = fileName;
    }
    protected boolean open() {
        try {
            in = new BufferedReader(new FileReader(resource));
        } catch(IOException e) {
            System.out.println("Can not open file!");
            return false;
        }
        return true;
    }
    protected void readContent() {
        try {
            if(in != null) {
                String str;
                while((str = in.readLine()) != null) {
                     System.out.println(str); 
                }
            }
        } catch(IOException e) {
            System.out.println("Read file error !");
        }
    }
    protected void close() {
        if(in != null) {
            try {
                in.close();
            } catch(IOException e) {
                System.out.println("IO error !");
            }
        }
    }
}

/**
 *  A concrete class extends AbstractRead
 *  This class can read HTML from a HTTP URL
 */
import java.io.*;
import java.net.*;

public class ReadHtml extends AbstractRead {
    private URLConnection conn;
    private BufferedReader in;

    public ReadHtml() {
    }
    public ReadHtml(String s) {
        resource = s;
    }

    public boolean open() {
        try {
            URL url = new URL(resource);
            conn = url.openConnection();
            in = new BufferedReader (
                            new InputStreamReader(conn.getInputStream()));
        } catch (MalformedURLException e) {
            System.out.println("Uable to connect URL:" + resource);
            return false;
        } catch (IOException e) {
            System.out.println("IOExeption when connecting to URL" + resource);
            return false;
        }
        return true;
    }
    protected void readContent() {
        try {
            if(in != null) {
                String str;
                while((str = in.readLine()) != null) {
                     System.out.println(str);
                }
            }
        } catch(IOException e) {
            System.out.println("Read file error !");
        }
    }
    protected void close() {
        if(in != null) {
            try {
                in.close();
            } catch(IOException e) {
                System.out.println("IO error !");
            }
        }
    }

}

 

/**
 *  A test client
 */
public class Test  {
    public static void main(String[] args) {
        // You should change the path of "test.txt" in your local machine
        String fileName = "d://test.txt";
        String url = "http://www.sina.com.cn";

        AbstractRead fileRead = new ReadFile();
        AbstractRead htmlRead = new ReadHtml();

        fileRead.setResource(fileName);
        htmlRead.setResource(url);

        System.out.println("-----  Read from a file  -----");
        fileRead.getContent();
        System.out.println("-----  Read from a url  -----");
        htmlRead.getContent();
    }
}