xml中的參數獲取

由於在servlet創建時沒有構造函數，當我們需要參數時可以使用初始化參數來初始化一些參數

在web.xml中添加<init-param>

<param-name>param1</param-name>
<param-value>param1</param-value>
</init-param>但是這些參數的作用域僅限於這個sevlet 不可以在多個servlet間共享

我們有兩種方法獲取servlet初始化參數

1 使用servlet的getInitParameter(String )方法 如果有，則返回他的值 沒有返回null

2 使用servletConfig對象的getInitParameter(String ）方法 返回值同上

    <servlet>
        <servlet-name>FristServlet</servlet-name>
        <servlet-class>qdm.test.FirstServlet</servlet-class>
        <init-param>
        <param-name>param1</param-name>
        <param-value>param1</param-value>
        </init-param>
        <init-param>
            <param-name>param2</param-name>
            <param-value>param2</param-value>
        </init-param>
        <init-param>
            <param-name>param3</param-name>
            <param-value>param3</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>FristServlet</servlet-name>
        <url-pattern>/servlet/FirstServlet</url-pattern>
    </servlet-mapping>

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("第一種方法獲取servlet初始化參數");
        String param1=getInitParameter("param1");
        String param2=getInitParameter("param2");
        String param3=getInitParameter("param3");
        System.out.println("param1"+param1);
        System.out.println("param2"+param2);
        System.out.println("param3"+param3);
        System.out.println("第二種方法獲取servlet初始化參數");
        ServletConfig config=getServletConfig();
        String p1=config.getInitParameter("param1");
        String p2=config.getInitParameter("param2");
        String p3=config.getInitParameter("param3");
        System.out.println("param1"+p1);
        System.out.println("param2"+p2);
        System.out.println("param3"+p3);
    }

運行結果如下

 

如果想在多個servlet間共享一些參數 則需要在上下文（context）設置初始化參數

<context-param>
 <param-name>context-name1</param-name>
 <param-value>context-value1</param-value>
</context-param>
我們可以通過getServletConfig().getServletContext()來獲取Context對象
然后通過調用getInitParameter(String )來獲取指定的參數 getIniteParameterNames()來獲取全部參數名稱

    <context-param>
        <param-name>context-name1</param-name>
        <param-value>context-value1</param-value>
    </context-param>
    <context-param>
        <param-name>context-name2</param-name>
        <param-value>context-value2</param-value>

 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("獲取context參數");
        ServletContext context=getServletContext();

        System.out.println("獲取全部參數");
        Enumeration names=context.getInitParameterNames();
        while(names.hasMoreElements())
        {
            String paraname=(String)names.nextElement();
            String paravalue=context.getInitParameter(paraname);
            System.out.println("參數名："+paraname+"-----值："+paravalue);
        }
    }

 

運行效果如圖