跳至主要内容

Servlet 4.0: Runtime Discovery of Servlet Mappings

Runtime Discovery of Servlet Mappings

When a servlet is activated, the mapping info can be discoverable at runtime.
Described in the Servlet spcefication.
The method getHttpServletMapping() on HttpServletRequest returns an HttpServletMapping implementation that provides information for the mapping that caused the current Servlet to be invoked. Please see the javadocs for the normative specification. Please see sections Section 9.3.1, “Included Request Parameters” on page 9-101Section 9.4.2, “Forwarded Request Parameters” on page 9-102 and Section 9.7.2, “Dispatched Request Parameters” on page 9-104 for relevant request attributes.
But please notice:
As with the included and forwarded request parameters, the HttpServletMapping is not available for servlets that have been obtained with a call to ServletContext.getNamedDispatcher().
An sample to print the mapping information of a servlet.
@WebServlet(name = "MyServlet",
        urlPatterns = {
            "/MyServlet",
            "/",
            "/path/*",
            "*.extension"
        }
)
public class MyServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {
        
          
        HttpServletMapping mapping = request.getHttpServletMapping();
         
        response.getWriter()
                .append("Mapping match:")
                .append(mapping.getMappingMatch().name())
                .append("\n")
                .append("Match value:")
                .append(mapping.getMatchValue())
                .append("\n")
                .append("Pattern:")
                .append(mapping.getPattern());
    }
}
Here is an example for demonstrating forward, async dispatch, and include.
@WebServlet(name = "ServletA",
        urlPatterns = {
            "/ServletA",
            "/AForwardToB",
            "/AIncludesB",
            "/AAsyncDispatchToB",
            "*.a"
        },
        asyncSupported = true
)
public class ServletA extends HttpServlet {

    public static void printCurrentMappingDetails(HttpServletRequest request,
            PrintWriter out) throws IOException {
            HttpServletMapping forwardMapping = (HttpServletMapping) request.getAttribute(RequestDispatcher.FORWARD_MAPPING);
            HttpServletMapping includeMapping = (HttpServletMapping) request.getAttribute(RequestDispatcher.INCLUDE_MAPPING);
            HttpServletMapping asyncMapping = (HttpServletMapping) request.getAttribute(AsyncContext.ASYNC_MAPPING);

            out.print("<p> " + request.getHttpServletMapping() + "</p>");
            out.print("<p> FORWARD_MAPPING: " + forwardMapping + "</p>");
            out.print("<p> INCLUDE_MAPPING: " + includeMapping + "</p>");
            out.print("<p> ASYNC_MAPPING: " + asyncMapping + "</p>");
            out.print("<hr />");


    }

    /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        HttpServletMapping mapping = request.getHttpServletMapping();

        if (mapping.getPattern().equals("/AForwardToB")) {
            RequestDispatcher rd = request.getRequestDispatcher("/ServletB");
            rd.forward(request, response);
            return;
        }

        if (mapping.getPattern().equals("/AAsyncDispatchToB")) {
            AsyncContext asyncContext = request.startAsync();
            asyncContext.dispatch("/ServletB");
            return;
        }

        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
            out.println("<!DOCTYPE html>");
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet ServletA</title>");
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Servlet ServletA at " + request.getContextPath() + "</h1>");

            printCurrentMappingDetails(request, out);

            if (mapping.getPattern().equals("/AIncludesB")) {
                RequestDispatcher rd = request.getRequestDispatcher("/ServletB");
                rd.include(request, response);
            }

            out.println("</body>");
            out.println("</html>");
        } finally {
            out.close();
        }
    }

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /**
     * Handles the HTTP <code>GET</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Handles the HTTP <code>POST</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Returns a short description of the servlet.
     *
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>

}

//Servlet B is a generic servlet.

@WebServlet(name = "ServletB", urlPatterns = {
    "/ServletB",
    "*.b"
})
public class ServletB extends HttpServlet {

    /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
            /* TODO output your page here. You may use following sample code. */
            out.println("<!DOCTYPE html>");
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet ServletB</title>");
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Servlet ServletB at " + request.getContextPath() + "</h1>");

            ServletA.printCurrentMappingDetails(request, out);

            out.println("</body>");
            out.println("</html>");
        } finally {
            out.close();
        }
    }

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /**
     * Handles the HTTP <code>GET</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Handles the HTTP <code>POST</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Returns a short description of the servlet.
     *
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>

}
Try to access ServletA with different urls(urlPatterns of WebServlet annotation on ServletA), which results in different mappings.
Grab the source codes from my github account, and have a try.
发表评论

此博客中的热门博文

JPA 2.1: Attribute Converter

JPA 2.1: Attribute Converter If you are using Hibernate, and want a customized type is supported in your Entity class, you could have to write a custom Hibernate Type. JPA 2.1 brings a new feature named attribute converter, which can help you convert your custom class type to JPA supported type. Create an Entity Reuse thePostentity class as example. @Entity @Table(name="POSTS") public class Post implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.AUTO) @Column(name="ID") private Long id; @Column(name="TITLE") private String title; @Column(name="BODY") private String body; @Temporal(javax.persistence.TemporalType.DATE) @Column(name="CREATED") private Date created; @Column(name="TAGS") private List<String> tags=new ArrayList<>(); } Create an attribute converter In this example…

Auditing with Hibernate Envers

Auditing with Hibernate Envers The approaches provided in JPA lifecyle hook and Spring Data auditing only track the creation and last modification info of an Entity, but all the modification history are not tracked. Hibernate Envers fills the blank table. Since Hibernate 3.5, Envers is part of Hibernate core project. Configuration Configure Hibernate Envers in your project is very simple, just need to addhibernate-enversas project dependency. <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-envers</artifactId> </dependency> Done. No need extra Event listeners configuration as the early version. Basic Usage Hibernate Envers provides a simple@Auditedannotation, you can place it on an Entity class or property of an Entity. @Audited private String description; If@Auditedannotation is placed on a property, this property can be tracked.

Spring Data Mongo: bridge MongoDB and Spring

Spring Data Mongo: bridge MongoDB and SpringMongoDBis one of the most popular NoSQL products, Spring Data Mongo(Maven archetype id is spring-data-mongodb) tries to provides a simple approach to access MongoDB. Configuration Add the following code fragments in your Spring configuration. <!-- Mongo config --> <mongo:db-factory id="mongoDbFactory" host="localhost" port="27017" dbname="conference-db" /> <bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate"> <constructor-arg ref="mongoDbFactory" /> </bean> <mongo:repositories base-package="com.hantsylabs.example.spring.mongo" /> Firstly, declare aDbFactorywhich is responsible for connecting to the MongoDB server. Then, register theMongoTemplateobject which envelop the data operations on MongoDB. Lastly addmongo:repositorieswith an essentialbase-packageattribute, Spring will discovery your d…