Servlet学习总结（二）

学习自孤傲苍狼的博客园

• ServletConfig
• ServletContext

ServletConfig的学习

ServletConfig的作用是让Servlet获得初始化的数据,在servlet的web.xml中可以通过<init-param>来为servlet配置初始化参数.

<servlet>
    <servlet-name>asda</servlet-name>
    <servlet-class>servleta.asda</servlet-class>
    <init-param>
        <param-name>name</param-name>
        <param-value>aaa</param-value>
    </init-param>
    <init-param>
        <param-name>pass</param-name>
        <param-value>aaaa</param-value>
    </init-param>
        <init-param>
        <param-name>acc</param-name>
        <param-value>aaaaaaa</param-value>
    </init-param>
</servlet>

当servlet配置好之后,创建一个servlet时会自动将这些数据初始化封装到ServletConfig中,调用
init方法时,数据会传给init的config参数中,通过ServletConfig的对象就可以取得数据.

@WebServlet("/asda")
public class asda extends HttpServlet {
    private static final long serialVersionUID = 1L;
    //通过ServletConfig接收参数
    private ServletConfig config;
    //init-param配置的数据会通过init方法中的config参数来获取
    @Override
    public void init(ServletConfig config) throws ServletException {
        this.config=config;
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取指定的一个数据
        String paramVal=this.config.getInitParameter("name");
        response.getWriter().print(paramVal);
        response.getWriter().print("</hr>");
        //获取所有数据
        Enumeration<String> e=config.getInitParameterNames();
        while(e.hasMoreElements()) {
            String name=e.nextElement();
            String value=config.getInitParameter(name);
            response.getWriter().println(name+"="+value);
        }
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

运行结果:

aaa

ccc=aaaaaaa

pass=aaaa

name=aaa

ServletContext的学习

ServletContext可以看做成一个被所有Servlet共享的全局容器,你可以通过Servletonfig.getServletContext获取ServletContext对象,来实现servlet之间的数据共享.
ServletContext的生命周期是整个web工程

实例:两个servlet通过ServletContext实现数据共享

public class ServletContextTest extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String data="傻狗！";
        //获取context实例
        ServletContext context=this.getServletConfig().getServletContext();
        //设置值到context中
        context.setAttribute("data", data);
        response.getWriter().println("aaa");

    }

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

public class ServletContextTest2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        //给获取的信息设置编码格式，这样就不会出现都是？？？的情况
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
                //获取context的实例
        ServletContext context=this.getServletContext();
        //获取“data”的数据
        String data=(String) context.getAttribute("data");
        response.getWriter().print(data);
        response.getWriter().println("aaa");
    }

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

web工程都是在tomcat下运行的,他们生命周期的运作都是基于开启同一个服务所产生的,所以运行第一个后关闭再重新开启运行第二个,tomcat里就不再存有第一个的值,第二个就会报null.

使用init方法必须重写写出父类方法super.init(config);去获取config,不然就会报空指针.

最后别忘了在web.xml下添加servlet的路径.