Oracle Java Magazine：探索Java EE 8，Servlet 4.0与Microprofile

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"Oracle Java Magazine 的 November/December 2017 期，这是一本专为Java开发者设计的杂志，涵盖了Java技术的最新发展和深入解析。本期主要讨论了Java方法动态调用、Java Card平台介绍、Java EE 8的新特性、CDI 2.0的依赖注入改进以及JPA 2.2的更新内容。" 在本期《Java Magazine》中，Java社区的专家们分享了一系列关键知识点： 1. **动态方法调用**：文章"Understanding Java Method Invocation with Invokedynamic"由Ben Evans撰写，深入探讨了Java 7引入的`invokedynamic`指令。这个新特性使得程序能够在运行时动态解析方法调用，极大地提高了代码的灵活性和效率，尤其在处理反射和动态语言支持时表现突出。 2. **Java Card平台**：Nicolas Ponsini和Florian Tournier介绍了Java Card的基础知识。Java Card是最小型的Java平台，广泛应用于智能卡和其他安全设备。文章揭示了其与传统应用程序开发的区别，让读者了解如何在受限环境中进行编程。 3. **Java EE 8**：Java Enterprise Edition 8 (Java EE 8) 是企业级Java应用的标准。文中详细阐述了Servlet 4.0、CDI 2.0、JPA 2.2以及MicroProfile等核心组件的新特性，为开发者提供了更强大的工具和框架来构建现代Web应用。 - **Servlet 4.0**：增强了对HTTP/2的支持，改进了API，使得服务器推送和WebSocket集成变得更加简单。 - **CDI 2.0**：Arjan Tijms的文章讲解了如何通过新的规范、功能和注解使依赖注入变得更简单，提升了开发者的生产力。 - **JPA 2.2**：Josh Juneau展示了Java Persistence API的新特性，如结果流式处理、日期转换的改进和新的注解，这些都显著提升了数据操作的便利性。 4. **Java Quiz**：Simon Roberts设计了一次挑战，测试读者的中级到高级Java语言知识，帮助他们巩固并提升Java编程技能。这期杂志全面覆盖了Java开发的各个方面，无论是对于刚接触Java的初学者，还是经验丰富的开发者，都能从中受益匪浅，了解最新的技术趋势和最佳实践。

ORACLE.COM/JAVAMAGAZINE /////////////////////////////// NOVEMBER/DECEMBER 2017

//java ee 8 /

request.newPushBuilder()

.path("images/coffee-cup.jpg")

.push();

getServletContext()

.getRequestDispatcher("/coffee-cup.jsp")

.forward(request, response); }}

Listing 2 shows the JSP web page:

Listing 2.

<html>

<head>

<title>Coffee-Cup</title>

</head>

<body>

</body>

</html>

In Listing 1, I have a servlet called SimplestExample and a JSP to which the servlet dispatches.

As you can see, the JSP page requires only one resource, the

coffee-cup.jpg image. When the

doGet() request handling method is invoked, it creates a new PushBuilder instance, sets the

image’s location, and calls the

push() method to send the resource to the client.

As the image is making its way to the client, the servlet is forwarding the request to the JSP

that requires the

coffee-cup.jpg resource. By the time the browser has received the rendered



another request.

To see Server Push in action, you can use the developer’s tools provided by Google’s Chrome



to the

SimplestExample servlet. You should see a result similar to that shown in Figure 1. You can

ORACLE.COM/JAVAMAGAZINE /////////////////////////////// NOVEMBER/DECEMBER 2017

//java ee 8 /

clearly see that the protocol it uses is h2 (short for “HTTP/2”) and the image was initiated via



TLS Required for HTTP/2

You might have noticed in Figure 1 that the scheme of the request is HTTPS. This is because all



-

cessful HTTP/2 communication. Browser vendors have made that decision on our behalf.

Care must be taken when using a new

PushBuilder object. A call to newPushBuilder() will

return

null if the connection is not secure, if the client does not support Server Push, or if the



SETTINGS frame.

If you want to try this example for yourself, you can clone the code from the GitHub

repository.

Anatomy of a PushBuilder

Each new instance of

PushBuilder created by calling newPushBuilder() is based upon the cur-

rent

HttpServletRequest instance. It is initiated with the HTTP GET method, and all headers are

stripped out except for

conditional, range, expect, authorization, and referrer headers.

PushBuilder implements the builder pattern where chained method calls are used to mutate

the instance before calling the

push()

Figure 1: Resource request satisﬁed by Server Push

ORACLE.COM/JAVAMAGAZINE /////////////////////////////// NOVEMBER/DECEMBER 2017

//java ee 8 /

this does not mean that your JSP web

applications are doomed to HTTP 1.1



bespoke solution.

You know that JSP pages are translated

into servlets and requests to those servlets



this knowledge, you can create a solution that allows you to harness the power of Server Push.



-

quent requests, the resources the page requires are pulled from the cache and pushed to the cli-







-

rer header and matching the referrer page name to the name of the initial page request, thus

building up a cache of page-to-resource locations.

-





The

HttpServletRequest



HttpServletRequest instance you can use a new instance of PushBuilder and start

pushing resources.

Runtime Discovery of Mappings



. Frameworks that need to know the exact map-



The runtime discovery of the URL mapping

that causes a servlet to be activated has been

reﬁned, thanks to the new Servlet Mapping API.

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