设计模式-模板方法(十三)

• 抽象类实现部分逻辑并定义抽象方法迫使子类实现剩余的逻辑,
  不同的子类只需完成抽象方法的不同实现,但是整个通用的逻辑已经在父类实现

模板方法使用的频率还是比较多的,比如我们导出一个文件或读取一个文件,总是会按照一定的流程的,比如一定要打开一个文件,最后可能都要关闭文件,可能还要记录一下日志,如果不用模板方法就会发现很多逻辑都要重新一遍,变动起来所有的地方也要改一下,模板方法就是为了解决这种对方法逻辑的共性抽象的.

• 上类图

  
  
  模板方法.png

• 代码示例:

1. 定义模板方法,这是模板方法的核心,里面会完成主要的逻辑骨架

package com.byedbl.template;

/**
 *  An abstract class which can get content from a file or a HTTP URL 
 *  or other resource  
 */
public abstract class AbstractRead {
    protected String resource;

    /**
     * 
     * 定义个模板方法,完成功能逻辑骨架,具体实现留到子类去实现
     * 完成逻辑的抽象
     **/
    public void getContent() {
        if(open()) {
            readContent();
            close();
        }
    }
    public void setResource(String s) {
        resource = s;
    }

    /**
     * 定义子类需要实现的抽象方法
     **/
    protected abstract boolean open();
    protected abstract void readContent();
    protected abstract void close();
}


子类实现其需要实现的抽象方法,

package com.byedbl.template;
/**
 * A concrete class extends AbstractRead
 * This class can read from a file
 */
import org.springframework.util.ClassUtils;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

/**
 * 一种实现,读文本
 * @author : zengzhijun
 * @date : 2018/5/25 13:57
 **/
public class ReadFile extends AbstractRead {
    private BufferedReader in = null;

    public ReadFile() {
    }

    public ReadFile(String fileName) {
        resource = fileName;
    }

    protected boolean open() {
        try {
            String file = ClassUtils.getDefaultClassLoader().getResource(this.resource).getFile();

            in = new BufferedReader(new FileReader(file));
        } 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 !");
            }
        }
    }
}

另一种实现
package com.byedbl.template; /**
 *  A concrete class extends AbstractRead
 *  This class can read HTML from a HTTP URL
 */
import java.io.*;
import java.net.*;

/**
 * 另一种实现,读URL
 * @author : zengzhijun
 * @date : 2018/5/25 13:57
 **/
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 !");
            }
        }
    }
    
}


客户端调用,客户端调getContent方法

package com.byedbl.template;

/**
 *  A test client
 */
public class Test  {
    public static void main(String[] args) {
        String fileName = "test.txt";
        String url = "http://www.baidu.com";
        
        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();
    }
}