學(xué)習(xí)自孤傲蒼狼的博客園

• ServletConfig
• ServletContext

ServletConfig的學(xué)習(xí)

ServletConfig的作用是讓Servlet獲得初始化的數(shù)據(jù),在servlet的web.xml中可以通過<init-param>來為servlet配置初始化參數(shù).

<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>

當(dāng)servlet配置好之后,創(chuàng)建一個servlet時會自動將這些數(shù)據(jù)初始化封裝到ServletConfig中,調(diào)用
init方法時,數(shù)據(jù)會傳給init的config參數(shù)中,通過ServletConfig的對象就可以取得數(shù)據(jù).

@WebServlet("/asda")
public class asda extends HttpServlet {
    private static final long serialVersionUID = 1L;
    //通過ServletConfig接收參數(shù)
    private ServletConfig config;
    //init-param配置的數(shù)據(jù)會通過init方法中的config參數(shù)來獲取
    @Override
    public void init(ServletConfig config) throws ServletException {
        this.config=config;
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //獲取指定的一個數(shù)據(jù)
        String paramVal=this.config.getInitParameter("name");
        response.getWriter().print(paramVal);
        response.getWriter().print("</hr>");
        //獲取所有數(shù)據(jù)
        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);
    }
}

運行結(jié)果:

aaa

ccc=aaaaaaa

pass=aaaa

name=aaa

ServletContext的學(xué)習(xí)

ServletContext可以看做成一個被所有Servlet共享的全局容器,你可以通過Servletonfig.getServletContext獲取ServletContext對象,來實現(xiàn)servlet之間的數(shù)據(jù)共享.
ServletContext的生命周期是整個web工程

實例:兩個servlet通過ServletContext實現(xiàn)數(shù)據(jù)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="傻狗铭乾！";
        //獲取context實例
        ServletContext context=this.getServletConfig().getServletContext();
        //設(shè)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");
        //給獲取的信息設(shè)置編碼格式乳乌，這樣就不會出現(xiàn)都是耍群？沐旨？巴席？的情況
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
                //獲取context的實例
        ServletContext context=this.getServletContext();
        //獲取“data”的數(shù)據(jù)
        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下運行的,他們生命周期的運作都是基于開啟同一個服務(wù)所產(chǎn)生的,所以運行第一個后關(guān)閉再重新開啟運行第二個,tomcat里就不再存有第一個的值,第二個就會報null.

使用init方法必須重寫寫出父類方法super.init(config);去獲取config,不然就會報空指針.

最后別忘了在web.xml下添加servlet的路徑.