Servlet 3.1实践

Servlet 3.1 新特性详解

参考:
- IBM developerworks: Servlet 3.0 新特性详解
- 开涛的博客: Servlet3.1规范（最终版）
关键特性
- Asynchronization(异步支持): 通过AsyncContext另起异步线程处理业务逻辑, 不再阻塞Filter或Servlet线程. 可以实现Reactor模式.
- Pluggability(插拨支持): 通过Annotation(@WebServlet, @WebFilter, @WebListener, @WebInitParam, @MultipartConfig, @ServletSecurity, @HttpConstraint, @HttpMethodConstraint)或/META-INF/web-fragment.xml充分解耦组件,实现插拨机制.
  注意: 在web.xml设置metadata-complete="true"可以关闭Pluggability特性. 但不影响@HandlesTypes+ServletContainerInitializer的动态注册机制.
- Fileupload(文件上传): 通过@MultipartConfig+Part实现文件上传. 不再需要apache-fileupload.
- Dynamic Registration(动态注册):
  - 通过ServletContext.addXXX()+Registration实现.
  - 相关API只能在ServletContextListener.contextInitialized()或者ServletContainerInitializer.onStartup()中调用. 后者是基于java服务API机制实现, 需要在(/META-INF/services/javax.servlet.ServletContainerInitializer)配置实现类.
  - 动态注册不受web.xml中metadata-complete="true"影响,但优先级低于web.xml, 相同设置会被覆盖.
以上4点是Servlet 3.0/3.1的关键特性, 其中
- Pluggabilityr的目标是"充分解耦,实现插拨"
- Dynamic Registration的目标是"动态注册,编程"
- Asynchronization的目标是提高并发性能
- FileUpload, Annotation是增加编程方便

Servlet 3.1 新特性练习

Jetty9对于Servlet 3.1的支持很不友善, 配置起来令人不舒服! 在Tomcat 7/8/9都支持Embedded. 后面使用Tomcat8(要求JDK7, 支持Servlet3.1/JSP2.3)练习.

准备工具: 配置嵌入式Tomcat

Maven依赖:

<properties>
	<spring.version>4.2.7.RELEASE</spring.version>
	<tomcat.version>8.5.5</tomcat.version>
</properties>

<dependencies>
	<!-- ================================ -->
	<!-- spring test frameworks -->
	<!-- ================================ -->
	<dependency>
	<groupId>org.springframework</groupId>
	<artifactId>spring-test</artifactId>
	<version>${spring.version}</version>
	</dependency>

	<!-- ================================ -->
	<!-- junit frameworks -->
	<!-- ================================ -->
	<!-- https://mvnrepository.com/artifact/junit/junit -->
	<dependency>
	<groupId>junit</groupId>
	<artifactId>junit</artifactId>
	<version>4.12</version>
	</dependency>

	<!-- https://mvnrepository.com/artifact/com.github.stefanbirkner/system-rules -->
	<dependency>
	<groupId>com.github.stefanbirkner</groupId>
	<artifactId>system-rules</artifactId>
	<version>1.16.1</version>
	</dependency>


	<!-- ================================ -->
	<!-- tomcat frameworks -->
	<!-- ================================ -->
	<!-- https://devcenter.heroku.com/articles/create-a-java-web-application-using-embedded-tomcat#add-a-launcher-class -->
	<dependency>
	<groupId>org.apache.tomcat.embed</groupId>
	<artifactId>tomcat-embed-core</artifactId>
	<version>${tomcat.version}</version>
	</dependency>
	<dependency>
	<groupId>org.apache.tomcat.embed</groupId>
	<artifactId>tomcat-embed-jasper</artifactId>
	<version>${tomcat.version}</version>
	</dependency>
	<dependency>
	<groupId>org.apache.tomcat.embed</groupId>
	<artifactId>tomcat-embed-websocket</artifactId>
	<version>${tomcat.version}</version>
	</dependency>
	<dependency>
	<groupId>org.apache.tomcat</groupId>
	<artifactId>tomcat-jasper</artifactId>
	<version>${tomcat.version}</version>
	</dependency>
	<dependency>
	<groupId>org.apache.tomcat</groupId>
	<artifactId>tomcat-jasper-el</artifactId>
	<version>${tomcat.version}</version>
	</dependency>
	<dependency>
	<groupId>org.apache.tomcat</groupId>
	<artifactId>tomcat-jsp-api</artifactId>
	<version>${tomcat.version}</version>
	</dependency>
</dependencies>
<build>
	<plugins>
		<plugin>
			<artifactId>maven-compiler-plugin</artifactId>
			<version>3.3</version>
			<configuration>
				<source>1.7</source>
				<target>1.7</target>
				<encoding>UTF-8</encoding>
			</configuration>
		</plugin>
		<plugin>
			<artifactId>maven-source-plugin</artifactId>
			<version>2.4</version>
			<executions>
				<execution>
					<id>attach-sources</id>
					<goals>
					<goal>jar</goal>
					</goals>
				</execution>
			</executions>
		</plugin>
	</plugins>
</build>

Java实现:

public final class EmbedTomcat extends RiseJUnitTester {

	public static final String WEBAPP_DIRECTORY = "src/main/webapp/";
	public static final String ROOT_CONTEXT = "";
	public static final int HTTP_PORT = 80;
	public static final int HTTPS_PORT = 443;
	public static final int OFF = -1;

	public static void start() {
		start(ROOT_CONTEXT, HTTP_PORT, OFF, null, null, null);
	}

	public static void start(int httpPort) {
		start(ROOT_CONTEXT, httpPort, OFF, null, null, null);
	}

	public static void start(String keyAlias, String password, String keystorePath) {
		start(ROOT_CONTEXT, OFF, HTTPS_PORT, keyAlias, password, keystorePath);
	}

	public static void start(int httpsPort, String keyAlias, String password, String keystorePath) {
		start(ROOT_CONTEXT, OFF, httpsPort, keyAlias, password, keystorePath);
	}

	public static void start(int httpPort, int httpsPort, String keyAlias, String password, String keystorePath) {
		start(ROOT_CONTEXT, httpPort, httpsPort, keyAlias, password, keystorePath);
	}

	public static void start(String contextPath, int httpPort, int httpsPort, String keyAlias, String password, String keystorePath) {

		// FIX: A context path must either be an empty string or start with a '/' and do not end with a '/'.
		if (contextPath == null || contextPath.equals("/")) {
			contextPath = ROOT_CONTEXT;
		}
		try {
			// initial
			processSystemEnvironment();

			Tomcat tomcat = new Tomcat();

			if (httpsPort > 0) {
				tomcat.setPort(httpsPort);
				Connector httpsConnector = tomcat.getConnector();
				httpsConnector.setSecure(true);
				httpsConnector.setScheme("https");
				httpsConnector.setAttribute("keyAlias", keyAlias);
				httpsConnector.setAttribute("keystorePass", password);
				httpsConnector.setAttribute("keystoreFile", keystorePath);
				httpsConnector.setAttribute("clientAuth", "false");
				httpsConnector.setAttribute("sslProtocol", "TLS");
				httpsConnector.setAttribute("SSLEnabled", true);

				if (httpPort > 0) {
					Connector httpConnector = new Connector();
					httpConnector.setPort(httpPort);
					httpConnector.setRedirectPort(httpsPort);
					tomcat.getService().addConnector(httpConnector);
				}
			} else if (httpPort > 0) {
				tomcat.setPort(httpPort);
			}

			StandardContext ctx = (StandardContext) tomcat.addWebapp(contextPath, new File(WEBAPP_DIRECTORY).getAbsolutePath());
			// Declare an alternative location for your "WEB-INF/classes" dir Servlet 3.0 annotation will work
			WebResourceRoot resources = new StandardRoot(ctx);
			resources.addPreResources(new DirResourceSet(resources, "/WEB-INF/classes", new File("target/classes").getAbsolutePath(), "/"));
			ctx.setResources(resources);
			ctx.setJarScanner(new WebappStandardJarScanner());
			ctx.setDefaultWebXml(new File("src/main/webapp/WEB-INF/web.xml").getAbsolutePath());
			// FixBug: no global web.xml found
			for (LifecycleListener ll : ctx.findLifecycleListeners()) {
				if (ll instanceof ContextConfig) {
					((ContextConfig) ll).setDefaultWebXml(ctx.getDefaultWebXml());
				}
			}

			tomcat.start();
			tomcat.getServer().await();
		} catch (Exception e) {
			throw new RuntimeException("tomcat launch failed", e);
		}
	}

}

代码功能:

支持http启动
支持https启动, 需用keytool创建keystore.
支持http + https启动, 其中http转发https.
以上用于测试

另外Tomcat自带的StandardJarScanner的processManifest()在jar的META-INF/manif.mf含有"Class-Path"项时处理不大正确. 复制其源码保存为WebappStandardJarScanner.java(package相同),并注释下述语句:

    private static final Set<ClassLoader> CLASSLOADER_HIERARCHY;

    static {
        Set<ClassLoader> cls = new HashSet<>();
		// FixBug: fail to scan
		// ClassLoader cl = WebappStandardJarScanner.class.getClassLoader();
		// while (cl != null) {
		// cls.add(cl);
		// cl = cl.getParent();
		// }

        CLASSLOADER_HIERARCHY = Collections.unmodifiableSet(cls);
    }

准备工作: 创建war项目

Maven配置

<dependencies>
		<!-- https://mvnrepository.com/artifact/org.eclipse.jetty.aggregate/jetty-all -->

		<!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
		<dependency>
			<groupId>javax.servlet</groupId>
			<artifactId>javax.servlet-api</artifactId>
			<version>3.1.0</version>
		</dependency>
		<!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
		<dependency>
			<groupId>javax.servlet.jsp</groupId>
			<artifactId>javax.servlet.jsp-api</artifactId>
			<version>2.3.1</version>
		</dependency>
        
        <!-- 准备工作: 嵌入式Tomcat -->
		<dependency>
			<groupId>com.yy.risedev</groupId>
			<artifactId>risedev-test</artifactId>
			<version>2.0.0</version>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>

		<plugins>
			<!-- compiler plugin -->
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.3</version>
				<configuration>
					<source>1.7</source>
					<target>1.7</target>
					<encoding>UTF-8</encoding>
				</configuration>
			</plugin>
			<!-- source plugin -->
			<plugin>
				<artifactId>maven-source-plugin</artifactId>
				<version>2.4</version>
				<executions>
					<execution>
						<id>attach-sources</id>
						<goals>
							<goal>jar</goal>
						</goals>
					</execution>
				</executions>
			</plugin>
			<plugin>
				<artifactId>maven-war-plugin</artifactId>
				<version>2.2</version>
				<configuration>
				    <!-- 无web.xml时maven检测错误 -->
					<failOnMissingWebXml>false</failOnMissingWebXml>
				</configuration>
			</plugin>
		</plugins>

	</build>

注意failOnMissingWebXml需要配置为false, 否则maven会显示表示错误的红叉叉...

练习1: web.xml 与 ServletContainerIntializer同时存在

在web.xml配置/test的Servlet,其类型为TestServlet2

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	version="3.0" metadata-complete="true">

	<servlet>
		<servlet-name>test</servlet-name>
		<servlet-class>servlet.TestServlet2</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>test</servlet-name>
		<url-pattern>/test</url-pattern>
	</servlet-mapping>

</web-app>

ServletContainerIntializer实现

在/META-INF/services/javax.servlet.ServletContainerInitializer设置实现类. 嗯! 就是一句话

servlet.MyServletContainerInitializer

MyServletContainerInitializer代码:

package servlet;

import java.util.Set;

import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.HandlesTypes;

@HandlesTypes(WebAppIntializer.class)
public class MyServletContainerInitializer implements ServletContainerInitializer {

	@Override
	public void onStartup(Set<Class<?>> arg0, ServletContext arg1) throws ServletException {
		for (Class<?> c : arg0) {
			if (WebAppIntializer.class.isAssignableFrom(c)) {
				try {
					((TestWebAppIntializer) (c.newInstance())).onStartup(arg1);
				} catch (InstantiationException | IllegalAccessException e) {
					e.printStackTrace();
				}
			}
		}
	}

}

WebAppIntializer代码:

package servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;

public interface WebAppIntializer {
	void onStartup(ServletContext ctx) throws ServletException;
}

TestWebAppIntializer代码:

package servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;

public class TestWebAppIntializer implements WebAppIntializer {

	public void onStartup(ServletContext ctx) throws ServletException {
		ServletRegistration.Dynamic dyna = ctx.addServlet("testServlet", "servlet.TestServlet");
		dyna.addMapping("/test");
	}

}

通过java服务API,会扫描@HandlesTypes的类型,然后传递给MyServletContainerInitializer.onStartup()执行. 假意相识的感觉? 这是Spring IOC的DI特性. 看来Spring的影响不小哦!

执行结果: 在访问http://localhost/test时,执行的是TestServlet的逻辑, 而非TestServlet2. 即web.xml配置覆盖了动态注册. 若改成/test2, 则能访问到动态注册的TestServlet2了. 同时, 也可看到metadata-complete="true"不影响动态注册.

练习2: web.xml与web-fragment.xml同时存在

/META-INF/web-fragment.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-fragment xmlns="http://java.sun.com/xml/ns/javaee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-fragment_3_0.xsd"
	version="3.0" metadata-complete="true">

	<servlet>
		<servlet-name>test</servlet-name>
		<servlet-class>servlet.TestServlet2</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>test</servlet-name>
		<url-pattern>/test2</url-pattern>
	</servlet-mapping>

</web-fragment>

/WEB-INF/web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	version="3.0" metadata-complete="false">

</web-app>

注意: metadata-complete="false", 否则pluggability特性会被关闭.

执行结果: 访问http://localhost/test,调用TestServlet2的业务逻辑,证明web-fragment.xml也会覆盖动态注册的

后续练习...

随时有想法都可以快速尝试

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原文地址：https://www.cnblogs.com/zolo/p/5912185.html