Servlet入门学习（三）

2023-11-16 12:29:10

经过前两篇的学习，我们知道了我们需要继承一个HttpServlet类，并且需要重写do Post与
do Get方法

public class ServletDemo extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

}

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

在重写过后会出现HttpServletRequest request与 HttpServletResponse response这么一串串东西；它们就是我们今天主要学习的请求对象与响应对象。

请求对象和响应对象，由服务器创建，管理，和销毁，服务器传给你，你只是拿来用

HttpServletResponse response：响应对象

HttpServletResponse response的意思是：响应对象；用来将响应的数据，封装进response 然后做出响应；
ServletRequest(接口) < --------继承 < -------HttpServletRequest(接口) < --------实现；

响应字符串数据：

获取字符打印流
在响应文本数据之前，设置响应编码
response.setCharacterEncoding(“utf-8”);
在告诉浏览器你用utf-8去解码
通过http协议来告诉浏览器，说白了就是，设置一个响应头
Content - Type: 键
text / html;charset = GB2312-- 告诉浏览器，服务器返回的文本采用什么编码值
response.setHeader(“Content-Type”,“text/html; charset=utf-8”);
以上两行代码，可以综合成一行,来设置响应中文的编码：
response.setContentType(“text/html; charset=utf-8”);

	@WebServlet(name = "ServletDemo2")
public class ServletDemo2 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("请求来了");

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

    PrintWriter writer = response.getWriter();
    writer.write("<h1 style='color:red'>Hello Welecome</h1>");

}

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

响应中文乱码的问题：

中文乱码：客户端和服务端的编码不一致
tomcat 服务器默认使用的编码是 ISO-8859-1

使用响应对象给浏览器响应字节数据：

来读取 WEB-INF 下的 xingye.jpg文件，然后使用字节流，把图片的字节数据，响应给浏览器

大体上分为三步走：
1：动态获取服务器路径；
2：获取字节输出流；
3：读写文件；

	@WebServlet(name = "ServletImage")
public class ServletImage extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    //动态获取服务器路径
    String realPath = this.getServletContext().getRealPath("/");
    System.out.println(realPath);
    FileInputStream in = new FileInputStream(realPath+"/WEB-INF/xingye.jpg");

    //获取字节输出流
    ServletOutputStream out = response.getOutputStream();

    //读写文件
    int len=0;
    byte[] bytes = new byte[1024];
    while ((len=in.read(bytes))!=-1){
        out.write(bytes,0,len);
        out.flush();
    }

    in.close();
    out.close();
}

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

HttpServletRequest request：请求对象

HttpServletRequest request的意思是：响应对象；由服务器创建管理和销毁，你只是拿来用；request 用来封装请求的信息，我们通过request就可以获取这些请求信息；

获取请求对象：

通过String queryString = request.getQueryString();

获取请求信息的一些方法:

获取客户端的ip:

String ip = request.getRemoteAddr();

获取协议:

String protocol = request.getProtocol();

获取请求的路径:

URI:统一资源标识符
URL:统一资源定位符
String requestURI = request.getRequestURI();
StringBuffer requestURL = request.getRequestURL();

动态获取项目的上下文路径:

String contextPath = request.getContextPath();

获取请求方式:

String method = request.getMethod();

@WebServlet(urlPatterns = "/demo2")
public class ServletDemo2 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=utf-8");
  
    //获取请求参数
    String queryString = request.getQueryString();
    System.out.println(queryString);
 
//获取客户端的ip
    String ip = request.getRemoteAddr();
    if(ip.equals("192.168.11.233")){
        response.getWriter().write("张三 你好");
    }else if(ip.equals("192.168.3.232")){
        response.getWriter().write("李四 你好");
    }else{
        response.getWriter().write("其他人 你好");
    }

    //获取协议
    String protocol = request.getProtocol();
    System.out.println(protocol);
    //获取请求的路径
    //URI:统一资源标识符
    //URL:统一资源定位符

    String requestURI = request.getRequestURI();
    StringBuffer requestURL = request.getRequestURL();
    System.out.println(requestURI);
    System.out.println(requestURL);


    //URL:协议：主机：端口：//资源
 
    //动态获取项目的上下文路径
    String contextPath = request.getContextPath();
    System.out.println(contextPath);

    //获取请求方式
    String method = request.getMethod();
    System.out.println(method);


 /*   1. 获取请求行:
    GET / MyServlet / index.jsp ? name = zhangsan & age = 23 HTTP / 1.1

    request.getMethod();//获取请求方式
    request.getContextPath();//获取项目名称
    request.getRequestURI();//获取URI
    request.getRequestURL();//获取URL
    request.getRemoteAddr();//获取IP地址
    request.getQueryString();//获取请求参数
    request.getProtocol();//获取协议版本*/



}

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

}

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