Java基础学习之Servlet 运用学习

Servlet 简介

Servlet 是什么？

Java Servlet 是运行在 Web 服务器或应用服务器上的程序，它是作为来自 Web 浏览器或其他 HTTP 客户端的请求和 HTTP 服务器上的数据库或应用程序之间的中间层。

使用 Servlet，您可以收集来自网页表单的用户输入，呈现来自数据库或者其他源的记录，还可以动态创建网页。

servlet 的优势:

性能明显更好。
Servlet 在 Web 服务器的地址空间内执行。这样它就没有必要再创建一个单独的进程来处理每个客户端请求。
Servlet 是独立于平台的，因为它们是用 Java 编写的。
服务器上的 Java 安全管理器执行了一系列限制，以保护服务器计算机上的资源。因此，Servlet 是可信的。
Java 类库的全部功能对 Servlet 来说都是可用的。它可以通过 sockets 和 RMI 机制与 applets、数据库或其他软件进行交互。

servlet 的架构:

servlet 的配置对象

一对象获取方式

方式一:

声明一个成员变量保存该对象

通过init方法获取ServletConfig对象

public class Demo01 extends HttpServlet {// 声明一个成员变量保存该对象private ServletConfig config;//给成员变量赋值@Overridepublic void init(ServletConfig config) throws ServletException {// TODO Auto-generated method stubsuper.init(config);this.config=config;}}

方式二:

直接调用父类的getServletConfig()方法

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {(直接调用父类的方法)ServletConfig config2 = this.getServletConfig();String value2 = config2.getInitParameter("weige");System.out.println(value2);}

作用:

获取Servlet的配置信息此对象是每个Servlet 都具有的;可通过该对象获取servlet的配置信息

private void fun1() {System.out.println(this.config);//可以通过ServletConfig对象获取Servlet的配置信息String value = this.config.getInitParameter("wanglong");System.out.println(value);//获取多个配置信息Enumeration<String> names = this.config.getInitParameterNames();while (names.hasMoreElements()) {System.out.println(names.nextElement());}

servlet 的域对象

servletContext :作用范围最大的域对象,作用域整个工程项目,并且此对象是个单例对象;

作用:可以利用单例的特点用来传值.该对象内部维护了一个map集合,而且所有的域对象内部都是维护了一个map集合;

1.存值取值 setAttribute getAttribute

2.获取全局配置信息

3.可以获取服务器上所有的资源的真实路径 getrealpath()

4.可以进行请求转发

该对象的获取方法

方式一: 通过ServletConfig 对象获取

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {ServletContext context = this.getServletConfig().getServletContext();//向context 保存一个值context.setAttribute("username", "wanglong");}

方式二:通过父类获取该方法在ServletConfig 接口中

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {ServletContext context = this.getServletContext();context.setAttribute("user", "我是王老五");//获取ServletContext 配置信息String value = context.getInitParameter("kuner");System.out.println(value);}

取值:

public class Demo03 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//取出Context域中的值ServletContext context = this.getServletConfig().getServletContext();Object obj = context.getAttribute("username");System.out.println(obj);}public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}

该域对象作用于整个工程,因此在该工程的任意的一个servlet 都可以获取到设置的值.

2.获取服务器上的资源路径

如上图在工程下不同的位置新建 a b c 三个properties文件

public class Demo04 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//fun1();//读取b and c.properties文件String path2 = this.getServletContext().getRealPath("/WEB-INF/classes/com/lanou3g/b.properties");String path3 = this.getServletContext().getRealPath("/WEB-INF/c.properties");System.out.println(path2);System.out.println(path3);//读文件FileInputStream fis2 = new FileInputStream(path2);Properties properties2 = new Properties();properties2.load(fis2);   FileInputStream fis3 = new FileInputStream(path3);Properties properties3 = new Properties();properties3.load(fis3);System.out.println(properties2.getProperty("key"));System.out.println(properties3.getProperty("key"));}private void fun1() throws FileNotFoundException, IOException {//读取a.properties 文件//参数路径是相对于工程名String path = this.getServletContext().getRealPath("/WEB-INF/classes/a.properties");System.out.println(path);//读文件FileInputStream fis = new FileInputStream(path);Properties properties = new Properties();properties.load(fis);System.out.println(properties.getProperty("key"));}public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}

4.请求转发

1.用户只发起了一次请求

2.用户请求是并不知道网站内部做了什么

public class Demo05 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("借点钱,萧峰兄弟");System.out.println("老兄:我没有 ,你去找坤儿");//通过context对象获取请求转发器//转发: 请求转发只能是站内转发(本工程) //并且转发的路径是相对于你的工程RequestDispatcher dispatcher = this.getServletContext().getRequestDispatcher("/demo06");//转发器//请求转发dispatcher.forward(request, response);System.out.println("钱借到了,人傻好办事");}public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

public class Demo06 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("我是坤儿,我有随便花");}public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

打印结果如下:

可以看出demo05 的需求被转发到 demo06 但是浏览器上并没有跳转到demo06;

响应 response

响应行响应的状态码 200 http协议 1.1

响应头告诉浏览器我要做什么操作 ?

告诉浏览器你需要使用什么编码格式来解析我的响应

响应体响应浏览器的内容

响应头设置应用

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//Tomcat默认的编码格式是 ISO-8859-1 不支持中文;/*response.setCharacterEncoding("utf-8");//设置响应头告诉浏览器你需要使用什么编码格式来解析数据response.setHeader("Content-type", "text/html;character=UTF-8");*///合并写法 (写Servlet 是第一句先写编码格式)response.setContentType("text/html;charset=UTF-8");//接到请求后向浏览器写个字符串//通过响应对象中的流对象回写//注意:;如果你当前在servlet中使用的字符流//那么就不能在写字节流了PrintWriter writer = response.getWriter();writer.write("wanglong你好啊");}

响应浏览器内容下载一张图片;

添加一张图片到工程内;

package com.lanou3g;import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.file.Path;import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/** 从服务器中下载图片*获取服务器的图片路径*读文件*通过respose 获取字节流回写**告诉浏览器(添加响应头)*1.我给的这个图片是下载用的*2.文件名 文件类型* content-disposition attachment;filename=content-type image/jpeg/png...*/
public class Demo08 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String path = this.getServletContext().getRealPath("/WEB-INF/classes/宝宝心里苦.png");File file = new File(path);String name = file.getName();//修改文件名的编码格式name = new String(name.getBytes(), "iso-8859-1");//添加响应头response.setHeader("content-disposition", "attachment;filename="+name);response.setHeader("content-type", "image/png");//读文件FileInputStream fis = new FileInputStream(path);ServletOutputStream out = response.getOutputStream();int len = 0;byte [] b = new byte [1024];while ((len = fis.read(b))!=-1) {out.write(b, 0, len);}fis.close();}public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

请求重定向

public class Demo09 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//fun1(response);//3秒后 跳转一个页面//添加一个刷新头//response.setHeader("refresh", "3;url=/sh-web-02/demo10");response.setIntHeader("refresh", 1);PrintWriter writer = response.getWriter();writer.write(Math.random()+"  ");}private void fun1(HttpServletResponse response) {System.out.println("我借钱");System.out.println("你去找demo10");//添加请求重定向  响应头//参数二是重定向的 路径(站内站外网址都可以)  站内路径需要带上工程名//response.setHeader("location", "/sh-web-02/demo10");response.setHeader("location", "http://baidu.com");//添加状态码302response.setStatus(302);System.out.println("借完了");}public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}

public class Demo10 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("我是demo10---找我借钱吗,门都没有");}public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

请求重定向

注意: 请求重定向是两次请求

第二次请求是接到第一次请求的响应头之后发生的可以看到浏览器中denmo09跳转到了demo10

请求 request

请求中的方法

     //获取请求的方式String method = request.getMethod();System.out.println(method);//获取请求的URLStringBuffer requestURL = request.getRequestURL();System.out.println(requestURL);//获取请求的URIString requestURI = request.getRequestURI();System.out.println(requestURI);//获取请求网址的相对路径String contextPath = request.getContextPath();System.out.println(contextPath);

使用 Servlet 读取表单数据并连接访问数据库

getParameter()：您可以调用 request.getParameter() 方法来获取表单参数的值。

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获取表单提交的数据//通过表单中 name属性 来获取输入框中的数据String username = request.getParameter("username");String password = request.getParameter("password");System.out.println(username);System.out.println(password);//连接数据库查询Connection conn = null;PreparedStatement statement  = null;ResultSet resultSet = null;String sql = "select * from user where username=? and password =?";try {conn = JDBCUtil.getConnection();statement = conn.prepareStatement(sql);statement.setObject(1, username);statement.setObject(2, password);resultSet = statement.executeQuery();if (resultSet.next()) {System.out.println("登录成功 欢迎" + username);}} catch (ClassNotFoundException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (SQLException e) {// TODO Auto-generated catch blocke.printStackTrace();}finally {//关闭资源JDBCUtil.closeAll(resultSet, statement, conn);}}