Servlet

转发【重点】

浏览器发送HTTP请求 => 服务器
服务器接收到请求之后内部资源处理跳转 => 服务器其他资源
服务器其他资源处理完毕之后，才通过原始的请求和响应返回数据 => 客户端

特征：

• ​ 转发是服务器行为
• ​ 转发情况下浏览器有且只发送了一次请求
• ​ 转发情况下浏览器的地址栏没有发生任何改变
• ​ 转发情况下，浏览器的请求数据是被保存的，是通过 request 进行传递的
• ​ 转发情况下有且只能转发 WEB Application 整个项目的内容资源

起始页

/**
 * 测试转发起始页
 */
@WebServlet("/TestForwardServletFrom")
public class TestForwardServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {
        // 设置自定义请求参数，保存到 request 中
        request.setAttribute("Forward", "转发成功");

        // 获取请求调度并器将 request 和 response 转发给 TestForWardServlet2
        request.getRequestDispatcher("TestForwardServletTo").forward(request, response);
    }
}

目的页

/**
 * 测试转发目的页
 */
@WebServlet("/TestForwardServletTo")
public class TestForwardServlet2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {
        // 获取请求参数
        Object context = request.getAttribute("Forward");

        System.out.println(context);

        response.setContentType("text/html; charset=utf-8");

        response.getWriter().append("我是目的页，这是从起始页传来的数据：" + context);
    }
}

URL 匹配原则

url-pattern匹配原则：
    1、精确匹配
        /具体名字
        
    2、后缀名匹配
        *.do *.action 
        *.xxx  
        主要是按照规定结尾的url-pattern都可以触发对应的Servlet程序
    
    3、通配符匹配
        /* 匹配所有请求，服务器端所有资源都可以匹配

精准匹配

案例代码

/**
 * 精准查询
 */
@WebServlet("/PreciseServlet")
public class PreciseServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {
        response.setContentType("text/html; charset=utf-8");
        response.getWriter().append("测试URL的精准查询：通过完整的协议+域名+端口+资源+参数");
    }
}

后缀名匹配

案例代码

/**
 * 后缀名匹配
 */
@WebServlet("*.do")
public class SuffixServlet  extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {
        response.setContentType("text/html; charset=utf-8");
        response.getWriter().append("测试URL的后缀名匹配，通过指定的后缀名即可");
    }
}

通配符匹配

/**
 * 通配符匹配
 */
@WebServlet("/*")
public class WildcardServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html; charset=utf-8");
        response.getWriter().append("通过通配符*的方式，所有路径都可以访问到");
    }
}

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