模板方法模式，定義一個操作中的算法的骨架，而將一些步驟延遲到子類中實現，使得子類可以不改變一個算法的結構即可重定義該算法的某些特定步驟。

UML示例

代碼示例

    package com.pattern;

public abstract class TemplateMethod {
	
	public static final String S1="method1";
	public static final String S2="method2";
	
	/**
	 * 模板方法
	 * @param methodName
	 */
	public final void Method(String methodName)
	{
		if(S1.equals(methodName))
		{
			Method1();
		}else if(S2.equals(methodName))
		{
			Method2();
		}
	}
	
	protected abstract void Method1();
	
	protected abstract void Method2();
	
}

  

    package com.pattern;

/**
 * 具體實現
 * @author jialin
 *
 */
public class Concrete extends TemplateMethod {

	protected void Method1() {
		System.out.println("Method1>>>>");
	}

	protected void Method2() {
		System.out.println("Method2>>>>");
	}
	

}

  

客戶端

    package com.pattern;

public class Client {
	public static void main(String[] args)
	{
		Concrete con=new Concrete();
		//con.Method("method1");
		con.Method("method2");
	}
}

  

模板方法在Servlet中有一個典型的應用就是HttpServlet

看一下它的源碼

把多余的代碼去掉，這是HttpServlet的部分代碼

    public abstract class HttpServlet extends GenericServlet {


    private static final String METHOD_DELETE = "DELETE";
    private static final String METHOD_GET = "GET";
    private static final String METHOD_POST = "POST";

    
    /**
     * Does nothing, because this is an abstract class.
     */
    public HttpServlet() {
        // NOOP
    }
    
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_get_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }



    protected void doHead(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        NoBodyResponse response = new NoBodyResponse(resp);

        doGet(req, response);
        response.setContentLength();
    }


    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_post_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }


   
    protected void doPut(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_put_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }


  
    protected void doDelete(HttpServletRequest req,
                            HttpServletResponse resp)
        throws ServletException, IOException {

        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_delete_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }
    
    protected void service(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        String method = req.getMethod();

        if (method.equals(METHOD_GET)) {
            long lastModified = getLastModified(req);
            if (lastModified == -1) {
                // servlet doesn't support if-modified-since, no reason
                // to go through further expensive logic
                doGet(req, resp);
            } else {
                long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
                if (ifModifiedSince < (lastModified / 1000 * 1000)) {
                    // If the servlet mod time is later, call doGet()
                    // Round down to the nearest second for a proper compare
                    // A ifModifiedSince of -1 will always be less
                    maybeSetLastModified(resp, lastModified);
                    doGet(req, resp);
                } else {
                    resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
                }
            }

        } else if (method.equals(METHOD_HEAD)) {
            long lastModified = getLastModified(req);
            maybeSetLastModified(resp, lastModified);
            doHead(req, resp);

        } else if (method.equals(METHOD_POST)) {
            doPost(req, resp);
            
        } else if (method.equals(METHOD_PUT)) {
            doPut(req, resp);        
            
        } else if (method.equals(METHOD_DELETE)) {
            doDelete(req, resp);
            
        } else if (method.equals(METHOD_OPTIONS)) {
            doOptions(req,resp);
            
        } else if (method.equals(METHOD_TRACE)) {
            doTrace(req,resp);
            
        } else {
            //
            // Note that this means NO servlet supports whatever
            // method was requested, anywhere on this server.
            //

            String errMsg = lStrings.getString("http.method_not_implemented");
            Object[] errArgs = new Object[1];
            errArgs[0] = method;
            errMsg = MessageFormat.format(errMsg, errArgs);
            
            resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
        }
    }

}

  

其中Service方法就是典型的模板方法，我們寫servlet的時候，一般要繼承HttpServlet,重新DoGet，DoPost等方法，跟模板方法模式思路一致。

模板方法模式（TemplateMethod）