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javaWeb03-请求转发和请求重定向【包含编码格式与路径问题】 - zwGitOne

 1 year ago
source link: https://www.cnblogs.com/zwgitOne123/p/17111194.html
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本文主要讲述javaWeb的请求转发和请求重定向的区别

一. 请求转发

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2. 代码示例

　　Servlet1的代码示例如下

public class Servlet1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Servlet1收到请求");
        req.setAttribute("key","Servlet1盖的章");
        req.getRequestDispatcher("/servlet2").forward(req,resp);
    }

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

    }
}

　　Servlet2的代码示例如下

public class Servlet2 extends HttpServlet {
    @Override
    // 请求转发，处理的是同一个请求
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object key = req.getAttribute("key");
        System.out.println("Servlet2收到了" + key);
        resp.getWriter().write("Servlet2响应的内容");
    }

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

    }
}

　　浏览器收到响应，显示结果如下

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　　响应response没有设置编码规则，导致默认的编码规则不支持中文字符，验证如下

public class Servlet2 extends HttpServlet {
    @Override
    // 请求转发，处理的是同一个请求
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object key = req.getAttribute("key");
        System.out.println("Servlet2收到了" + key);
        System.out.println(resp.getCharacterEncoding());
        resp.getWriter().write("Servlet2响应的内容");
    }

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

    }
}

　　tomcat日志如下

Servlet1收到请求
Servlet2收到了Servlet1盖的章
ISO-8859-1

　　由此看出，字符集是ISO-8859-1应该不支持中文字符

　　将resp的字符集设置为utf-8，声明如下

resp.setCharacterEncoding("utf-8");

　　浏览器收到响应，显示结果如下，仍是乱码

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　　resp响应设置了字符集utf-8，但是浏览器编码格式不是utf-8，而是windos-1252。字符集不相同，导致乱码

　　由思考和思考2，引出问题：如何保证浏览器和响应resp的字符集相同呢？

　　首先介绍Content-Type

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　　Servlet2声明如下

public class Servlet2 extends HttpServlet {
    @Override
    // 请求转发，处理的是同一个请求
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object key = req.getAttribute("key");
        System.out.println("Servlet2收到了" + key);
        // 解决浏览器与resp响应的编码格式不一致问题：
        // 方式一:
        resp.setHeader("Content-Type","text/html;charset=utf-8");
        // 方式二:
        resp.setContentType("text/html;charset=utf-8");
        resp.getWriter().write("Servlet2响应的内容");
    }

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

    }
}

　　① 请求转发，一直是同一个请求【请求的数据可以共享】

　　② 在resp响应浏览器内容时，如果有中文字符，则在响应之前，需要设置content-type，即 resp.setContentType("text/html;charset=utf-8");

二. 请求重定向

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2. 代码示例

　　Servlet1的代码示例如下

public class Servlet1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Servlet1收到请求");
        System.out.println("Servlet1请求重定向给Servlet2");
        resp.sendRedirect("/servlet2");
    }

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

    }
}

　　Servlet2的代码示例如下

public class Servlet2 extends HttpServlet {
    @Override
    // 请求转发，处理的是同一个请求
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Servlet2收到请求");
        System.out.println("请求路径为: ");
        StringBuffer requestURL = req.getRequestURL();
        System.out.println(requestURL);
    }

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

    }
}

　　浏览器收到响应，结果如下

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　　请求重定向的路径写的不对，下面解释一下 " / "

　　在浏览器中，" / "是指 http://localhost:8080，即http://ip地址:端口号

　　在web项目中，" / "是指http://localhost:8080/javaWeb03，即http://ip地址:端口号/项目名称 

　　Servlet1声明如下

public class Servlet1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Servlet1收到请求");
        System.out.println("Servlet1请求重定向给Servlet2");// 解决方式1：相对路径
        resp.sendRedirect("/javaWeb02/servlet2");
        // 解决方式2：绝对路径
        resp.sendRedirect("http://localhost:8080/javaWeb02/servlet2");
    }

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

    }
}

　　tomcat日志结果如下

Servlet1收到请求
Servlet1请求重定向给Servlet2
Servlet2收到请求
请求路径为: 
http://localhost:8080/javaWeb02/servlet2

　　① 注意浏览器和web项目中的" / "的不同含义；

　　② 请求重定向是浏览器向服务器发了两次请求


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