跳至主要内容

Servlet 4.0: Http Trailer

Http Trailer

Servlet 4.0 added Http Trailer(RFC 7230) supports, which is a specific collection of http headers comes after response body.
It is useful in some case, such as chunked transfer encoding or implements some specific protocols.
  • The reading side, HttpServletRequest has a method isTrailerFieldsReady() to check if the trailer fields are available, if it returns true, the trailer fields can be read via getTrailerFields() method.
  • The writing side, HttpServletResponse has a method setTrailerFields, which accpets a Supplier as it's parameter.
An example of Http Trailer to handle chunked tranfer encoding.
@WebServlet("/test")
public class TestServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        res.setContentType("text/plain");
        res.addHeader("Transfer-encoding", "chunked");
        res.addHeader("TE", "trailers");
        res.addHeader("Trailer", "bar");

        StringBuilder sb = new StringBuilder();

        final InputStream in = req.getInputStream();
        int b;
        while ((b = in.read()) != -1) {
            sb.append((char) b);
        }

        String foo = null;
        int size = -1;

        if (req.isTrailerFieldsReady()) {
            Map<String, String> reqTrailerFields = req.getTrailerFields();
            size = reqTrailerFields.size();
            foo = reqTrailerFields.get("foo");
        }

        final String finalFoo = foo;
        final int finalSize = size;
        res.setTrailerFields(() -> {
            Map<String, String> map = new HashMap<>();
            map.put("bar", finalFoo + finalSize);
            return map;
        });
        res.getWriter().write(sb.toString());
    }
}
A client to send chunked data.
@WebServlet("")
public class ClientServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        res.setContentType("text/plain");
        StringBuilder sb = new StringBuilder();

        String hostStr = req.getServerName();
        int port = req.getServerPort();

        try (
            Socket socket = new Socket(hostStr, port);
            OutputStream output = socket.getOutputStream();
            InputStream input = socket.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(input))
        ) {
            String reqStr = (new StringBuffer("POST /ee8-servlet-trailer/test HTTP/1.1\r\n")).
                append("Host: " + hostStr + "\r\n").
                append("Transfer-encoding: chunked\r\n").
                append("Connection: close\r\n").
                append("trailer: foo\r\n").
                append("\r\n").
                append("5\r\n").
                append("hello\r\n").
                append("0\r\n").
                append("foo: A\r\n").
                append("\r\n").
                toString();

            output.write(reqStr.getBytes(Charset.forName("US-ASCII")));

            String line = null;
            while ((line = reader.readLine()) != null) {
                if (line.startsWith("bar")) {
                    sb.append(line).append("\r\n");
                }
            }
        }

        res.getWriter().write(sb.toString());
    }
}
Grab the source codes from my github account, and have a try.

评论

此博客中的热门博文

Activating CDI in JSF 2.3

Activating CDI in JSF 2.3 When I upgraded my Java EE 7 sample to the newest Java EE 8, the first thing confused me is the CDI beans are not recoganized in Facelects template in a JSF 2.3 based web applicaiton, which is working in the development version, but in the final release version, they are always resolved as null. I filed an issue on Mojarra and discussed it with the developers from communities and the JSF experts. According to the content of README , In a JSF 2.3 application, to activate CDI support, declaring a 2.3 versioned faces-config.xml and adding javax.faces.ENABLE_CDI_RESOLVER_CHAIN in web.xml is not enough, you have to declare @FacesConfig annotated class to enable CDI. Here is the steps I created a workable JSF 2.3 applicatoin in Java EE 8. Create a Java web application, this can be done easily by NetBeans IDE, or generated by Maven archetype, for exmaple. $ mvn archetype:generate -DgroupId=com.example -DartifactId=demo -DarchetypeArtifactId=mav

JSF 2.3:Websocket support

Websocket support One of the most attractive features is JSF 2.3 added native websocket support, it means you can write real-time applications with JSF and no need extra effort. To enable websocket support, you have to add javax.faces.ENABLE_WEBSOCKET_ENDPOINT in web.xml . < context-param > < param-name >javax.faces.ENABLE_WEBSOCKET_ENDPOINT</ param-name > < param-value >true</ param-value > </ context-param > Hello Websocket Let's start with a simple example. @ViewScoped @Named ( " helloBean " ) public class HelloBean implements Serializable { private static final Logger LOG = Logger . getLogger( HelloBean . class . getName()); @Inject @Push PushContext helloChannel; String message; public void sendMessage () { LOG . log( Level . INFO , " send push message " ); this . sendPushMessage( " hello " ); } private

Build a Reactive application with Angular 5 and Spring Boot 2.0

I have created a post to describe Reactive programming supports in Spring 5 and its subprojects, all codes of this article are updated the latest Spring 5 RELEASE, check spring-reactive-sample under my Github account. In this post, I will create a simple blog system, including: A user can sign in and sign out. An authenticated user can create a post. An authenticated user can update a post. Only the user who has ADMIN role can delete a post. All users(including anonymous users) can view post list and post details. An authenticated user can add his comments to a certain post. The backend will be built with the latest Spring 5 reactive stack, including: Spring Boot 2.0, at the moment the latest version is 2.0.0.M7 Spring Data MongoDB supports reactive operations for MongoDB Spring Session adds reactive support for WebSession Spring Security 5 aligns with Spring 5 reactive stack The frontend is an Angular based SPA and it will be generated by Angular CLI. The so