2.深入学习Servlet的ServletContext对象
一.建立项目servlet01
在入门Servlet项目中建立一个子项目模块(此处不再赘述如何建立),补全maven项目中的java和resources文件夹,添加类HelloServlet.java,添加web.xml中的映射关系,添加tomcat (注意保持只有一个jar包方式把所有项目的jar都打进来了,删除其他项目的jar包,添加自己的jar包),运行验证是否搭建正确!
二.ServletContext对象
在web容器启动时,它会为每一个web程序创建一个对应的ServletContext对象,用来代表当前的web的应用。
ServletContext对象的几个重点所用:
共享数据:对于几个不同的Servlet之间可以相互传递数据
获取初始化参数:在web.xml中配置的参数,可以被或得到
请求转发:获得请求转发给别的Servlet
读取资源文件:此处需要注意配置资源过滤防止读取不了资源文件
1.共享数据: 在servlet中保存的数据可以在另一个servlet中被访问
例子:
在HelloServlet中代码
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // this.getInitParameter(); 初始化参数
// this.getServletConfig(); Servlet配置
// this.getServletContext(); Servlet上下文 ServletContext context = this.getServletContext(); String username = "小王";
context.setAttribute("username",username); //将数据存入ServletContext中 }
在GetServlet中的代码
public class GetServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletContext context = this.getServletContext(); String username = (String) context.getAttribute("username"); //获取别的Servlet所保存的参数,实现数据共享 resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
resp.getWriter().println("名字"+ username); } @Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
配置web.xml
<!--注册Servlet-->
<servlet>
<servlet-name>getc</servlet-name>
<servlet-class>ustc.wzh.servlet.GetServlet</servlet-class>
</servlet> <!--Servlet的请求路径-->
<servlet-mapping>
<servlet-name>getc</servlet-name>
<url-pattern>/getc</url-pattern>
</servlet-mapping>
启动tomcat执行程序
先执行http://localhost:8080/servlet01/hello 此时已经存入数据了,在执行http://localhost:8080/servlet01/getc 显示数据
执行成功!
2.获取初始化参数配置
新建Java类为GetParam
public class GetParam extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletContext context = this.getServletContext(); String url = (String) context.getInitParameter("url");
resp.getWriter().println(url); } @Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
在web.xml中编写初始化配置项和映射路径
<!--配置一些web应用初始化参数-->
<context-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
</context-param> <!--注册Servlet-->
<servlet>
<servlet-name>getParam</servlet-name>
<servlet-class>ustc.wzh.servlet.GetParam</servlet-class>
</servlet> <!--Servlet的请求路径-->
<servlet-mapping>
<servlet-name>getParam</servlet-name>
<url-pattern>/getParam</url-pattern>
</servlet-mapping>
重新部署tomcat,获取参数成功!
3.请求转发
新建Java类为GetRequestForward
public class GetRequestForward extends HttpServlet { @Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println("开始请求转发!");
ServletContext context = this.getServletContext(); //设置请求转发路径,再调用forward实现请求转发
context.getRequestDispatcher("/getParam").forward(req,resp); System.out.println("转发成功!");
} @Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
在web.xml中编写映射路径
<!--注册Servlet-->
<servlet>
<servlet-name>getReqFor</servlet-name>
<servlet-class>ustc.wzh.servlet.GetRequestForward</servlet-class>
</servlet> <!--Servlet的请求路径-->
<servlet-mapping>
<servlet-name>getReqFor</servlet-name>
<url-pattern>/getReqFor</url-pattern>
</servlet-mapping>
重新部署tomcat,转发成功!
4.读取资源文件
预处理:
由于我们在java目录下建立的properties和resources目录下建立的properties都被打报道同一路径下:classes,我们俗称这个路径为classpath;
1.建立properties文件:在resources目录下建立db.properties,在java目录下建立aa.properties
username=wzh password=123456
username=wzh02 password=123456890
2.修改当前项目下的pom.xml文件,添加配置
<!--在build中配置resources,来防止我们资源导出失败的问题-->
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
</resources>
3.编写读取配置文件的类:GetText
public class GetText extends HttpServlet { @Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //读取resources目录下的db.properties内容
InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties"); Properties properties = new Properties();
properties.load(in);
String username = properties.getProperty("username");
String password = properties.getProperty("password"); resp.getWriter().println(username + ":" + password); //读取java目录下的aa.properties内容
InputStream in2 = this.getServletContext().getResourceAsStream("/WEB-INF/classes/ustc/wzh/servlet/aa.properties"); Properties properties2 = new Properties();
properties2.load(in2);
String username2 = properties2.getProperty("username");
String password2 = properties2.getProperty("password"); resp.getWriter().println(username2 + ":" + password2); } @Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
注意:两个文件名是Rebuild project之后产生的
修改web.xml中的映射关系
<!--注册Servlet-->
<servlet>
<servlet-name>getText</servlet-name>
<servlet-class>ustc.wzh.servlet.GetText</servlet-class>
</servlet> <!--Servlet的请求路径-->
<servlet-mapping>
<servlet-name>getText</servlet-name>
<url-pattern>/getText</url-pattern>
</servlet-mapping>
重新部署tomcat,读取资源文件成功!
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