Servlet——ServletContext

一、ServletConfig：javax.servlet.ServletContext包；

　　// in the corresponding application jsp

　　// which defines a number of methods that can exchange data and Servlet exchange Rocchi and Tomcat;

　　// ServletContext jvm current web application and only allows sharing of data among a plurality of the Servlet;

Second, get ServletContext objects:

　　(1 ) by GenericServlet provided GetServletContext ();

　　　　//this.getServletContext()；

　　(2 ) by ServletConfig provided GetServletContext ();

　　　　//this.getServletConfig().getServletContext()；

　　(3 ) by obtaining the HttpServletRequest;

　　　　//req.getServletContext()；

　　(4 ) by acquiring the HttpSession;

　　　　//req.getSession().getServletContext()；

 Fourth, the method of operation of the data: // domain method includes the property method;

　　1. Set the properties: void setAttribute (String name, Object Object); // call with a name attribute more than once will be covered;

　　2. acquiring property: Object getAttribute (String name); // Gets the property name had not set return null;

　　3. Delete Attribute: void removeAttribute (String name);

　　4. Get all the domain of attribute names: the Enumeration getAttributeNames ();

@WebServlet("/test")
public class Test extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取ServletContext对象
        ServletContext servletContext = getServletContext();
        //设置属性
        servletContext.setAttribute("name", "zs");
        servletContext.setAttribute("name", "ww");
        servletContext.setAttribute("age", 14);
        //获取指定属性
        System.out.println(servletContext.getAttribute("name"));
        //删除属性
        servletContext.removeAttribute("name");
        //获取所有属性
        Enumeration<String> attributeNames = servletContext.getAttributeNames();
        while (attributeNames.hasMoreElements()) {
            String name = attributeNames.nextElement();
            Object value = servletContext.getAttribute(name);
            System.out.println(name+":"+value);
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

Fifth, access to resources Method : 

　　( 1 ) get the project name: String getContextPath ();

　　　　// Returns the name of the beginning of the project include / slash;

　　( 2 ) obtain the real path: String getRealPath (String path);

　　　　// incoming path before must contain slashes; "/a.txt"

　　( 3 all resources path) Gets the path: the Set getResourcePaths ( "/ the WEB-INF");

　　( 4 ) access to resources stream: the InputStream the getResourceAsStream ( "/ the WEB-INF / b.txt");

　　(5 ) acquires a parameter value: String the getInitParameter (String name);

　　　　// returns the current value of the initialization parameter in accordance with a program name included; <context-param>

　　(6 ) obtain the parameter values: the Enumeration <String> the getInitParameterNames ()  

　　　　// returns a reference to the current enumeration of all the names in the program initialization parameters (collection);

　　(7 ) obtains the encoded: String getRequestCharacterEncoding ();

　　(8 ) set the encoding: void setRequestCharacterEncoding (String encoding);

@WebServlet ( "Test" )
 public  class the Test the extends the HttpServlet { 
    @Override 
    protected  void the doGet (the HttpServletRequest REQ, the HttpServletResponse RESP) throws ServletException, IOException {
         // Get ServletContext object; 
        ServletContext where servletContext = GetServletContext ();
         // returns the name of the project, with / slash; / Review 
        String contextPath = servletContext.getContextPath (); 
        System.out.println (contextPath); 
        // returns true path of the file; E: \ JavaProject \ review2 \ Web \ index.jsp 
        String = realpath ServletContext.getRealPath ( "/index.jsp" );
        System.out.println(realPath);
        //返回路径下所有资源路径；
        Set<String> resourcePaths = servletContext.getResourcePaths("/WEB-INF");
        for (Iterator<String> iterator = resourcePaths.iterator(); iterator.hasNext(); ) {
            String next = iterator.next();
            System.out.println(next);
        }
        //获取资源流
        InputStream stream = servletContext.getResourceAsStream("/WEB-INF/b.txt");
        System.out.println(stream);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}