javaweb开发（六）：servlet请求转发、重定向、EL表达式

• 构建1个web项目，导入依赖

• 编写TestServlet

@WebServlet(name = "testServlet",urlPatterns = {"/test"})
public class TestServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter printWriter = resp.getWriter();
        printWriter.write("<div> TestServlet doGet </div>");
    }

}

• 配置端口
  

• 测试
  

• 请求转发

• 新建1个admin.jsp

• 编写DispatchServlet

@WebServlet("/forward")
public class DispatchServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("DispatchServlet doGet");
        req.getRequestDispatcher("/WEB-INF/admin.jsp").forward(req,resp);
    }

}

• 启动项目测试

# 访问http://localhost:8080/index.jsp可以访问到页面
# 访问http://localhost:8080/admin.jsp无法访问页面
# 访问http://localhost:8080/WEB-INF/admin.jsp无法访问页面
# 访问http://localhost:8080/forward可以访问页面admin.jsp

# servlet内部转发

• 转发到其他servlet

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("DispatchServlet doGet");
        req.getRequestDispatcher("request").forward(req,resp);
    }

• 测试

http://localhost:8080/forward?userName=jack&age=11&sport=ball&sport=sleep

• 控制台打印

DispatchServlet doGet
应用上下文路径 getContextPath=
客户端发出请求时的完整URL getRequestURL=http://localhost:8080/request
请求行中的资源名部分 getRequestURI=/request
请求行中的参数部分 getQueryString=userName=jack&age=11&sport=ball&sport=sleep
发出请求的客户机的IP地址 getRemoteAddr=0:0:0:0:0:0:0:1
客户机发请求使用的网络端口号 getRemotePort=51171
获取请求头 getHeader(Accept)=text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
客户端请求参数 getParameter=jack
客户端请求参数列表,多个值 getParameterValues=[Ljava.lang.String;@57d4dac
客户端请求参数封装成的map类型 getParameterMap=org.apache.catalina.util.ParameterMap@68a7bf4d

• EL表达式

# DispatchServlet中编写入下
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("DispatchServlet doGet");
        req.setAttribute("name","xdclass");
        req.getRequestDispatcher("/index.jsp").forward(req,resp);
    }

• index.jsp中获取领域对象中值

name = ${name}

• 启动测试

# 直接访问index.jsp不能获取到领域对象中的值
http://localhost:8080/index.jsp
# 访问时使用重定向可获取到领域对象中值
http://localhost:8080/forward

• 新建1个实体类

public class User {
    private int id;
    private String name;
    private String host;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getHost() {
        return host;
    }

    public void setHost(String host) {
        this.host = host;
    }

}

• 编写servlet

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("DispatchServlet doGet");
        User user = new User();
        user.setHost("https://xdclass.net");
        user.setId(1);
        user.setName("老王");
        req.setAttribute("user",user);
        req.getRequestDispatcher("/index.jsp").forward(req,resp);
    }

• 编写index.jsp

  name = ${user.name}
  id= ${user.id}
  host= ${user.host}

• 启动测试

http://localhost:8080/forward

• 重定向，是一个外部的转发，有2次请求，无法获取到领域对象中的值

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("DispatchServlet doGet");
        req.setAttribute("name","jack");
        resp.sendRedirect("/index.jsp");
    }

• 测试