【Servlet-2】HttpServletResponse接口

web服务器收到一个Http请求后，会针对每个请求创建一个HttpServletRequest对象和HttpServletResponse对象，如果需要获取客户端提交请求的相关信息，需要从HTTPServletRequest对象中获取，如果需要向客户端发送数据，则需要通过HttpServletResponse对象来文成。

1.向客户端发送数据

ServletResponse有一个方法getWriter()，用于获取到一个输出流对象PrintWriter，专门用于向客户端输出数据的，称为标准输出流。

package HttpServletResponse;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/ServletResponseDemo1")
public class ServletResponseDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取标准输出流
        PrintWriter out = response.getWriter();

        //向输出流中写入数据，客户端浏览器就会看到这些数据
        out.println("<h1>abc</h1>");
        out.print("我爱中国");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

可以通过设置响应的编码类型：
response.setContentType("text/html;charset=UTF-8");

	response.setContentType("text/html;charset=UTF-8");
      //获取标准输出流
      PrintWriter out = response.getWriter();

      //向输出流中写入数据，客户端浏览器就会看到这些数据
      out.println("<h1>abc</h1>");
      out.print("我爱中国");

2.请求转发与重定向

通过HTTPServletRequest获取到的RequestDispatcher对象的forward()方法，可以完成请求转发功能。而通过HttpServletResponse的sendRedirect()方法，可以完成重定向功能。


请求转发与重定向均是指请求的跳转方式：
请求转发也称为服务器内部跳转
重定向也称为服务器外部跳转

Forward文件：请求转发到OtherServlet文件
在里面设置域属性，在OtherServlet文件中可以取到域属性的值

package 请求转发;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/Forward")
public class Forward extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String age = request.getParameter("age");
        //设置域属性
        request.setAttribute("name",name);
        request.setAttribute("age",age);
        request.getRequestDispatcher("/OtherServlet").forward(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

OtherServlet文件：在转发的文件中取到域属性的值

package 请求转发;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/OtherServlet")
public class OtherServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        out.print("otherServlet......");

        Object name = request.getAttribute("name");
        Object age = request.getAttribute("age");
        out.println("name="+name);
        out.println("age="+age);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

重定向：

package 响应重定向;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/Redirect")
public class Redirect extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("执行Redirect。。。。");
        //重定向
        response.sendRedirect("/34/RedirectServlet");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

package 响应重定向;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/RedirectServlet")
public class RedirectServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.print("执行RedirectServlet.....");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

通过上面的视频可看出，重定向地址栏地址改变了。

请求转发：
　浏览器只发出一次请求，收到一次响应
　请求转发到的资源中可以直接获取请求中所携带的数据
　浏览器地址栏显示的用户所提交的请求路径
　只能跳转到当前应用的资源中
　
重定向：
　浏览器发出两次请求，接收到两次响应
　重定向到的资源不能直接获取到用户提交请求中所携带的数据
　浏览器地址栏显示的为重定向的请求路径，而非用户提交请求的路径
　重定向不仅可以跳转到当前应用的其他资源，也可以跳转到其他应用中资源