4.2.2 获取初始化参数

可以用来配置一些web应用初始化参数

注意：实际工作中一般不在web.xml中放参数，而用properties文件等存全局参数

happyContextParam


admin




setByConf


setByConfValue



package com.happy.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class GetInitParamsServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
ServletContext servletCOntext= this.getServletContext();
String setByCOnf= (String)servletContext.getInitParameter("setByConf");
response.setCharacterEncoding("utf-8");
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.println("setByConf："+setByConf);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}
}


4.2.3 请求转发

实际工作中一般不用ContextServlet对象的dispatcher，而用response对象的dispatcher方法

package com.happy.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class ContextDispatcherServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
ServletContext servletCOntext= this.getServletContext();
servletContext.getRequestDispatcher("/get").forward(request,response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}
}



ContextDispatcherServlet
com.happy.servlet.ContextDispatcherServlet


ContextDispatcherServlet
/cds



4.2.4 读取项目资源文件

实际工作中一般不用这个api，而是用反射和类加载等加载资源文件

前景补充知识

关于classpath

• java目录，作为source目录


• resources目录，作为resources目录

对回被打包到同一个路径下：classes，我们俗称这个路径为classpath：

maven构建时候，部分source目录下面资源文件不能打包问题

解决方案：在build中配置resources.来防止我们资源导出失败的问题




src/main/resources

**/*.properties
**/*.xml

true


src/main/java

**/*.properties
**/*.xml

true





获取资源文件

写一个servlet调用context对象的获取资源文件的api方法getResourceAsStream

InputStream is = servletContext.getResourceAsStream("/WEB-INF/classes/db.properties");


PropertiesServlet
com.happy.servlet.PropertiesServlet


PropertiesServlet
/ps



package com.happy.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
public class PropertiesServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
ServletContext servletCOntext= this.getServletContext();
InputStream is = servletContext.getResourceAsStream("/WEB-INF/classes/db.properties");
Properties prop = new Properties();
prop.load(is);
String url = prop.getProperty("url");
String username = prop.getProperty("username");
String password = prop.getProperty("password");
response.getWriter().println(url+" "+username+" "+password);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}
}


效果如下：

4.3 HttpServletResponse

web服务器接收到客户端的http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的一个httpServeletResponse。

• 如果要获取客户端请求过来的参数：找HttpServeletRequest


• 如果要给客户端响应一些信息：找HttpServeletResponse

4.3.1 HttpServletResponse简单分类

负责向浏览器发送数据的方法

ServletOutputStream getOutputStream() throws IOException; //其他，如果老用中文会造成字符窜丢失
PrintWriter getWriter() throws IOException; //中文


负责向浏览器设置响应头方法

void setCharacterEncoding(String var1);
void setContentLength(int var1);
void setContentLengthLong(long var1);
void setContentType(String var1);
void setBufferSize(int var1);
void setDateHeader(String var1, long var2);
void addDateHeader(String var1, long var2);
void setHeader(String var1, String var2);
void addHeader(String var1, String var2);
void setIntHeader(String var1, int var2);
void addIntHeader(String var1, int var2);
void setStatus(int var1);


响应的状态码：

int SC_COnTINUE= 100;
int SC_SWITCHING_PROTOCOLS = 101;
int SC_OK = 200;
int SC_CREATED = 201;
int SC_ACCEPTED = 202;
int SC_NON_AUTHORITATIVE_INFORMATION = 203;
int SC_NO_COnTENT= 204;
int SC_RESET_COnTENT= 205;
int SC_PARTIAL_COnTENT= 206;
int SC_MULTIPLE_CHOICES = 300;
int SC_MOVED_PERMANENTLY = 301;
int SC_MOVED_TEMPORARILY = 302;
int SC_FOUND = 302;
int SC_SEE_OTHER = 303;
int SC_NOT_MODIFIED = 304;
int SC_USE_PROXY = 305;
int SC_TEMPORARY_REDIRECT = 307;
int SC_BAD_REQUEST = 400;
int SC_UNAUTHORIZED = 401;
int SC_PAYMENT_REQUIRED = 402;
int SC_FORBIDDEN = 403;
int SC_NOT_FOUND = 404;
int SC_METHOD_NOT_ALLOWED = 405;
int SC_NOT_ACCEPTABLE = 406;
int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
int SC_REQUEST_TIMEOUT = 408;
int SC_COnFLICT= 409;
int SC_GOnE= 410;
int SC_LENGTH_REQUIRED = 411;
int SC_PRECONDITION_FAILED = 412;
int SC_REQUEST_ENTITY_TOO_LARGE = 413;
int SC_REQUEST_URI_TOO_LOnG= 414;
int SC_UNSUPPORTED_MEDIA_TYPE = 415;
int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
int SC_EXPECTATION_FAILED = 417;
int SC_INTERNAL_SERVER_ERROR = 500;
int SC_NOT_IMPLEMENTED = 501;
int SC_BAD_GATEWAY = 502;
int SC_SERVICE_UNAVAILABLE = 503;
int SC_GATEWAY_TIMEOUT = 504;
int SC_HTTP_VERSION_NOT_SUPPORTED = 505;


4.3.2 HttpServletResponse常见应用

1. 向浏览器输出消息

2.下载文件resp.setHeader("Content-disposition","attachment;filename"+filename);

核心：

resp.setHeader("Content-disposition","attachment;filename="+filename);


URLEncoder.encode(filename,"utf-8")) //解决文件名乱码


1. 要获取下载文件的路径


2. 下载文件名是啥


3. 设置想办法让浏览器能够支持下载我们需要的东西


4. 获取下载文件的输入流


5. 创建缓存区


6. 获取OutputStream对象


7. 将FIleOutputStream流写入到buffer缓冲区


8. 使用outputstream将缓冲区中的数据输出到客户端

package com.happy.servlet;
import org.apache.commons.lang3.StringUtils;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
public class DownServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/* 1. 要获取下载文件的路径
2. 下载文件名是啥
3. 设置想办法让浏览器能够支持下载我们需要的东西
4. 获取下载文件的输入流
5. 创建缓存区
6. 获取OutputStream对象
7. 将FIleOutputStream流写入到buffer缓冲区
8. 使用outputstream将缓冲区中的数据输出到客户端*/
String realPath = this.getServletContext().getRealPath("/WEB-INF/classes/书.jpg");
System.out.println(realPath);
String filename = realPath.substring(realPath.lastIndexOf("\\") + 1);
System.out.println(filename);
// resp.setHeader("Content-disposition","attachment;filename"+filename);
String userAgent = req.getHeader("USER-AGENT");
if (StringUtils.contains(userAgent, "MSIE") || StringUtils.contains(userAgent, "Edge")) {
// IE浏览器
filename = URLEncoder.encode(filename, "UTF-8");
} else if (StringUtils.contains(userAgent, "Firefox") || StringUtils.contains(userAgent, "Chrome") || StringUtils.contains(userAgent, "Safari")) {
// google,火狐浏览器
// filename = new String(filename.getBytes(), "ISO-8859-1");
filename = URLEncoder.encode(filename, "UTF-8");
} else {
filename = URLEncoder.encode(filename, "UTF-8");
// 其他浏览器
}
System.out.println(filename);
resp.setHeader("Content-disposition", "attachment;filename=" + filename);
// 创建输入流,把文件变成流
FileInputStream is = new FileInputStream(realPath);
// 创建输出流
ServletOutputStream os = resp.getOutputStream();
// 创建缓存区，new 一个byte【】作为byte
byte[] buff = new byte[1024];
int len = 0;
try {
System.out.println("开始读取数据");
while ((len = is.read(buff)) > 0) {
os.write(buff, 0, len);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
is.close();
os.close();
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}


3.生成验证码

原生生成验证码方法：

package com.happy.servlet;
import org.junit.jupiter.api.Test;
import javax.imageio.ImageIO;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
public class ImageServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 前端刷新为windows.location.refresh
// 通过后端响应给前端设置头信息，响应可以设置前端所有东西
response.setHeader("refresh","8");
BufferedImage bufferedImage=drawNum();
// 告诉浏览器，这个请求的响应用图片方式打开
response.setContentType("image/png");
// 取消缓存
response.setDateHeader("expires",-1);
response.setHeader("Cache-Control","no-cache");
response.setHeader("Pragma","no-cache");
boolean jpg = ImageIO.write(bufferedImage, "jpg", response.getOutputStream());
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
@Test
public BufferedImage drawNum(){
// 在内存中创建一个空白的图片
BufferedImage bufferedImage = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
Graphics2D graphics = (Graphics2D) bufferedImage.getGraphics();
// 设置图片的背景颜色
graphics.setColor(Color.white);
// 画边框
graphics.fillRect(0,0,80,20);
// 给图片写数据
graphics.setColor(Color.blue);
graphics.setFont(new Font(null,Font.BOLD,20));
graphics.drawString(makeNum(),0,20);
return bufferedImage;
}
public String makeNum(){
Random random = new Random();
String num = String.valueOf(random.nextInt(999999+1));
StringBuffer sb = new StringBuffer(num);
for(int i=0;i<=5-num.length();i++){
sb.append(0);
}
return sb.toString();
}
}


4.实现重定向

本质上是302和location设置重定向地址

response.sendRedirect();


常见场景：

• 用户登陆

package com.happy.servlet;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
public class RedirectServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 方式一
// 可以直接重定向到外部网站
// response.sendRedirect("http://www.baidu.com");
// 也可以内部地址，要带项目名
response.sendRedirect("/response/image");
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}
}


所以本质上是302和location设置重定向地址

// 方式二，拆分两步
response.setHeader("Location","/response/image");
// response.setStatus(302);
response.setStatus(HttpServletResponse.SC_FOUND);


重定向和转发的区别

${pageContext.request.contextPath}

登陆跳转（重定向实战）

index.jsp作为登陆页面如下：

<%@ page cOntentType="text/html;charset=UTF-8" language="java" %>





<%--这里提交的路径，需要寻找项目的路径--%>
<%----%>

用户：
密码：






web.xml配置映射


FormServlet
com.happy.servlet.FormServlet


FormServlet
/login



处理servlet

package com.happy.servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class FormServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("进入这个请求了");
String username = request.getParameter("username");
String password = request.getParameter("password");
System.out.println(username+":"+password);
response.sendRedirect("/response/success.jsp");
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}
}


4.4 HttpServletRequest

4.4.1 响应重定向和请求转发

重定向和转发的区别

重定向response.sendRedirect

注意：重定地址（外部地址）要带项目名

获取方式：

1. 写死response.sendRedirect("projectContextName/success.jsp");

   
   



2. this.getServletContext().getContextPath()
response.sendRedirect(this.getServletContext().getContextPath()+"/success.jsp");

   




3. request.getContextPath()
response.sendRedirect(request.getContextPath()+"/success.jsp");

   

转发request.getRequestDispatcher

注意：转发地址（内部地址）不用带项目名

转发this.getServletContext().getRequestDispatcher

4.4.2 获取前端参数

package com.happy.servlet;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.util.Arrays;
public class LoginServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String username = request.getParameter("username");
String password = request.getParameter("password");
System.out.println(username+":"+password);
String[] hobbies = request.getParameterValues("hobbies");
System.out.println(Arrays.toString(hobbies));
System.out.println(this.getServletContext().getContextPath());
System.out.println(request.getContextPath());
// 方式一：response redirect转发
// response.sendRedirect(this.getServletContext().getContextPath()+"/success.jsp");
// 方式二：servletContext 重定向
// this.getServletContext().getRequestDispatcher("/success.jsp").forward(request,response);
//方式三：request 重定向
request.getRequestDispatcher("/success.jsp").forward(request,response);
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
}