7-1 渐行渐远的Servlet
Spring5开始支持WebFlux，把以前Java Web应用开发从Servlet必 选变成可选，一个是Servlet Web,另外一个是React Web(WebFlux)
技术回顾
传统Servlet部署
通过web.xml 传统Servlet组件
Servlet API本身FilterListener:ServletContextListener HandlerMethodReturnValueHandler
关于异步Servlet实现 DispatcherServletWeb自动装配
什么是 Servlet？
Servlet是一种基于Java技术的 Web组件，用于生成动态内容，由容器管理。类似于其他Java技术组件，Servlet是平台无关的 Java类组成，并且由 Java Web服务器加载执行。通常情况，由 Servlet 容器提供运行时环境。Servlet容器，有时候也称作为 Servlet引擎，作为Web服务器或应用服务器的一部分。通过请求和响应对话，提供Web客户端与 Servlets交互的能 力。容器管理Servlets实例以及它们的生命周期。 从功能上，Servlet介于 CGI（Common Gateway Interface）与服务扩展（如：Netscape Server API或 Apache模块）之间。 在体系上，Servlet技术（或者规范）属于Java EE技术（规范）的一部分。不过 Servlet 并非一开始就隶属于 J2EE或者Java EE。接下来的小节将会介绍 Servlet各个版本。
Servlet版本
规范版本发布时间Java 平台主要更新
Servlet 4.02017 年 9 月Java EE 8支持 HTTP/2Servlet 3.12013 年 5 月Java EE 7非阻塞 I/O、HTTP 协议更新机制（WebSocket）Servlet 3.02009 年 12 月Java EE 6可插拔、简化部署、异步 Servlet、安全、文件上传Servlet 2.52005 年 9 月Java EE 5Annotation 支持Servlet 2.42003 年 11月J2EE 1.4web.xml 支持 XML SchemeServlet 2.32001 年 8月J2EE 1.3新增 Filter、事件/监听器、WrapperServlet2.2 1999 年 8月J2EE 1.2作为 J2EE 的一部分， 以 .war 文件作为独立 web 应用
7-2 Servlet 核心 API
核心组件API 说明起始版本Spring Framework 代表实现
javax.servlet.Servlet动态内容组件1.0DispatcherServletjavax.servlet.FilterServlet 过滤器2.3CharacterEncodingFilterjavax.servlet.ServletContextServlet应用上下文javax.servlet.AsyncContext异步上下文3.0无javax.servlet.ServletContextListenerServletContext 生命周期监听器2.3ContextLoaderListenerjavax.servlet.ServletRequestListenerServletRequest生命周期监听器2.3RequestContextListenerjavax.servlet.http.HttpSessionListenerHttpSession 生命周期监听器2.3HttpSessionMutexListenerjavax.servlet.AsyncListener异步上下文监听器3.0StandardServletAsyncWebRequestjavax.servlet.ServletContainerInitializerServlet 容器初始化器3.0SpringServletContainerInitializer
7-4 Servlet 注册
注册方式传统方式注解方式编程方式
Servlet注册web.xml部署 <servlet> + <servlet-mapping>@WebServletServletContext#addServletFilter注册web.xml部署 <filter> + <filter-mapping>@WebFilterServletContext#addFilter*Listener注册web.xml部署 <listener>@WebListenerServletContext#addListener
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/webapp_2_5.xsd"
metadata-complete="true" version="2.5">
<context-param>
<description>
Spring 配置文件路径参数，该参数值将被 org.springframework.web.context.ContextLoaderListener 使用
</description>
<param-name>contextConfigLocation
</param-name>
<param-value>
classpath*:/META-INF/spring/spring-context.xml
</param-value>
</context-param>
<listener>
<description>
org.springframework.web.context.ContextLoaderListener 为可选申明Listener
</description>
<listener-class>
org.springframework.web.context.ContextLoaderListener
</listener-class>
</listener>
</web-app>
7-5 理解 Servlet 组件生命周期
理解 Servlet生命周期
初始化：init(ServletConfig)服务： service(ServletRequest,ServletResponse)销毁： destroy()
DispatcherServlet初始化过程
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.statediagram-cluster.statediagram-cluster-alt .inner{fill:#e0e0e0}#mermaid-svg-6AuZnnpzWmNqMSzy .statediagram-cluster .inner{rx:0;ry:0}#mermaid-svg-6AuZnnpzWmNqMSzy .statediagram-state rect.basic{rx:5px;ry:5px}#mermaid-svg-6AuZnnpzWmNqMSzy .statediagram-state rect.divider{stroke-dasharray:10,10;fill:#efefef}#mermaid-svg-6AuZnnpzWmNqMSzy .note-edge{stroke-dasharray:5}#mermaid-svg-6AuZnnpzWmNqMSzy .statediagram-note rect{fill:#fff5ad;stroke:#aa3;stroke-width:1px;rx:0;ry:0}:root{--mermaid-font-family: '"trebuchet ms", verdana, arial';--mermaid-font-family: "Comic Sans MS", "Comic Sans", cursive}#mermaid-svg-6AuZnnpzWmNqMSzy .error-icon{fill:#522}#mermaid-svg-6AuZnnpzWmNqMSzy .error-text{fill:#522;stroke:#522}#mermaid-svg-6AuZnnpzWmNqMSzy .edge-thickness-normal{stroke-width:2px}#mermaid-svg-6AuZnnpzWmNqMSzy .edge-thickness-thick{stroke-width:3.5px}#mermaid-svg-6AuZnnpzWmNqMSzy .edge-pattern-solid{stroke-dasharray:0}#mermaid-svg-6AuZnnpzWmNqMSzy .edge-pattern-dashed{stroke-dasharray:3}#mermaid-svg-6AuZnnpzWmNqMSzy .edge-pattern-dotted{stroke-dasharray:2}#mermaid-svg-6AuZnnpzWmNqMSzy .marker{fill:#333}#mermaid-svg-6AuZnnpzWmNqMSzy .marker.cross{stroke:#333}
:root { --mermaid-font-family: "trebuchet ms", verdana, arial;}
#mermaid-svg-6AuZnnpzWmNqMSzy {
color: rgba(0, 0, 0, 0.75);
font: ;
}
HttpServlet.init()
HttpServletBean.init()
FrameworkServlet.initServletBean()
FrameworkServlet.initWebApplicationContext()
DispatcherServlet.onRefresh()
DispatcherServlet.initStrategies()
Servlet 初始化生命周期调用
将 ServletConfig 参绑定到Servlet 字段
初始化 Servlet 关联的 WebApplicationContext
触发 DispatcherServlet onRefresh
初始化 DispatcherServlet 各种组件
HttpServlet.init()
HttpServletBean.init()
FrameworkServlet.initServletBean()
FrameworkServlet.initWebApplicationContext()
DispatcherServlet.onRefresh()
DispatcherServlet.initStrategies()
DispatcherServlet 初始化过程
理解 Filter生命周期
初始化： init(FilterConfig)服务： doFilter(ServletRequest,ServletResponse,FilterChain)销毁： destroy()
理解 ServletContext生命周期
初始化： contextInitialized(ServletContextEvent)销毁： contextDestroyed(ServletContextEvent）
7-6 Servlet 异步支持
DeferredResult支持
DeferredResult——异步请求处理
新建项目spring-servlet
配置pom文件
pom.xml
<packaging>war
</packaging>
<dependencies>
<dependency>
<groupId>javax.servlet
</groupId>
<artifactId>javax.servlet-api
</artifactId>
<scope>provided
</scope>
</dependency>
<dependency>
<groupId>org.springframework
</groupId>
<artifactId>spring-webmvc
</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.tomcat.maven
</groupId>
<artifactId>tomcat7-maven-plugin
</artifactId>
<version>2.1
</version>
<executions>
<execution>
<id>tomcat-run
</id>
<goals>
<goal>exec-war-only
</goal>
</goals>
<phase>package
</phase>
<configuration>
<path>/
</path>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
配置文件
DefaultAnnotationConfigDispatcherServletInitializer.java
@ComponentScan(basePackages
= "com.whaleson.web.controller")
public class DefaultAnnotationConfigDispatcherServletInitializer extends
AbstractAnnotationConfigDispatcherServletInitializer {
@Override
protected Class
<?>[] getRootConfigClasses() {
return new Class[0];
}
@Override
protected Class
<?>[] getServletConfigClasses() {
return new Class[]{
getClass()
};
}
@Override
protected String
[] getServletMappings() {
return new String[]{"/"};
}
}
Controller
HelloWorldAsyncController.java
@RestController
public class HelloWorldAsyncController {
@GetMapping("/show/msg")
public DeferredResult
<String> showAsync(){
DeferredResult
<String> result
= new DeferredResult<>();
result
.onCompletion(()->{
println("I'm Completion!");
});
println("Hello Everyone!!!");
result
.setResult("Hello Everyone!!!");
return result
;
}
public static void println(Object object
){
String threadName
= Thread
.currentThread().getName();
System
.out
.println("当前线程的名称是[" + threadName
+ "]内容是:" + object
);
}
}
运行
打包
mvn -Dmaven.skip.test -U clean package
运行
java -jar target\spring-servlet-0.0.1-SNAPSHOT-war-exec.jar
浏览器输入Get请求地址
http://localhost:8080/show/msg
浏览器输出结果
Hello Everyone!!!
控制台输出结果
当前线程的名称是[http-bio-8080-exec-2]内容是:Hello Everyone!!! 当前线程的名称是[http-bio-8080-exec-2]内容是:I'm Completion!
结论
当前程序还是同步的，因为是同一个线程。
7-9 DeferredResult 异步执行
实现方式
激活()将结果放到另外一个线程
DefaultAnnotationConfigDispatcherServletInitializer.java -)AbstractAnnotationConfigDispatcherServletInitializer.java -)AbstractDispatcherServletInitializer.registerDispatcherServlet() -) registration.setAsyncSupported(this.isAsyncSupported());
代码实现
HelloWorldAsyncController.java
@RestController
@EnableScheduling
public class HelloWorldAsyncController {
private final BlockingQueue
<DeferredResult
<String>> queue
= new ArrayBlockingQueue<DeferredResult
<String>>(5);
private final Random random
= new Random();
@Scheduled(fixedRate
= 5000)
public void process() throws InterruptedException
{
DeferredResult
<String> result
= null
;
do{
result
= queue
.take();
long timeout
= random
.nextInt(3000);
Thread
.sleep(timeout
);
result
.setResult("Happy Every Day!");
println("执行计算结果"+ timeout
+ "ms");
}while (result
!= null
);
}
@GetMapping("/show/msg")
public DeferredResult
<String> showAsync() throws Exception
{
DeferredResult
<String> result
= new DeferredResult<>(50L
);
queue
.offer(result
);
println("Hello Everyone!!!");
result
.onCompletion(()->{
println("I'm Completion!");
});
result
.onTimeout(()->{
println("I'm Timeout");
});
return result
;
}
public static void println(Object object
){
String threadName
= Thread
.currentThread().getName();
System
.out
.println("当前线程的名称是[" + threadName
+ "]内容是:" + object
);
}
}
执行结果
当前线程的名称是[http-bio-8080-exec-1]内容是:Hello Everyone!!! 当前线程的名称是[http-bio-8080-exec-3]内容是:I'm Timeout 十月 24, 2020 3:05:15 下午 org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver logException警告: Resolved [org.springframework.web.context.request.async.AsyncRequestTimeoutException] 当前线程的名称是[http-bio-8080-exec-3]内容是:I'm Completion! 当前线程的名称是[pool-1-thread-1]内容是:执行计算结果2000ms
7-10 Callable 异步执行
@GetMapping("/callable")
public Callable
<String> callableHelloWorld(){
println("Hello World ! My girl!");
long startTime
= System
.currentTimeMillis();
return () ->{
println("执行程序消耗时间\t" + (System
.currentTimeMillis() -startTime
));
return "hello world";
};
}
缺点
没有回调；需要回调建议使用ListenableFutureCallback
7-11 CompletionStage 异步执行
关于CompletionStage<T>接口
它的实现有CompletableFuture<T>
HelloWorldAsyncController
@GetMapping("/completable")
public CompletionStage
<String> completionStageHelloWorld(){
long startTime
= System
.currentTimeMillis();
println("Hello CompletableFuture ! ");
return CompletableFuture
.supplyAsync(()-> {
println("执行程序消耗时间\t" + (System
.currentTimeMillis() -startTime
));
return "Goodbye CompletableFuture !";
});
}
浏览器地址
http://localhost:8080/completable
输出结果
当前线程的名称是[http-bio-8080-exec-4]内容是:Hello CompletableFuture ! 当前线程的名称是[ForkJoinPool.commonPool-worker-1]内容是:执行程序消耗时间17
7-12 MVC 异步支持原理分析
Spring Web MVC异步Servlet实现原理
HandlerMethodReturnValueHandlerServlet 3.0 AsyncContextDispatcherServlet整合
7-13 异步 Servlet 实现
Java Specification Requests (JSR)
自定义Servlet继承HttpServlet
public class AsyncServlet extends HttpServlet {
}
添加类注解WebServlet
@WebServlet
激活异步特性
asyncSupported = true
添加映射
urlPatterns = "/async-servlet"
重写service方法
判断当前请求是否支持异步
req.isAsyncSupported()
创建AsyncContext
AsyncContext asyncContext = req.startAsync();
添加监听器
asyncContext.addListener()
@WebServlet(
asyncSupported
= true,
urlPatterns
= "/async-servlet"
)
public class AsyncServlet extends HttpServlet {
@Override
public void service(HttpServletRequest req
, HttpServletResponse resp
) throws ServletException
, IOException
{
if (req
.isAsyncSupported()) {
println("Hey man.");
AsyncContext asyncContext
= req
.startAsync();
asyncContext
.setTimeout(50L
);
asyncContext
.addListener(new AsyncListener() {
@Override
public void onComplete(AsyncEvent event
) throws IOException
{
println("complete");
}
@Override
public void onTimeout(AsyncEvent event
) throws IOException
{
println("timeout");
}
@Override
public void onError(AsyncEvent event
) throws IOException
{
println("error");
}
@Override
public void onStartAsync(AsyncEvent event
) throws IOException
{
println("start");
}
});
HttpServletResponse response
=(HttpServletResponse
) asyncContext
.getResponse();
response
.setContentType("text/plain;charset=UTF-8");
PrintWriter printWriter
= response
.getWriter();
printWriter
.println("Hello");
printWriter
.flush();
}
}
public static void println(Object object
) {
String threadName
= Thread
.currentThread().getName();
System
.out
.println("当前线程的名称是[" + threadName
+ "]内容是:" + object
);
}
}
浏览器地址
http://localhost:8080/async-servlet
浏览器内容
Hello
控制台内容
当前线程的名称是[http-bio-8080-exec-1]内容是:Hey man. 当前线程的名称是[http-bio-8080-exec-3]内容是:timeout 当前线程的名称是[http-bio-8080-exec-3]内容是:complete
7-14 DefferedResult 实现原理
DeferredResultMethodReturnValueHandler
7-15 Spring Boot 嵌入式 Servlet 容器限制
Servlet 特性兼容性解决方案
web.xml不支持RegistrationBean 或 @Bean 注册ServletContainerInitializer不支持ServletContextInitializer@WebServlet 等有限支持依赖 @ServletComponentScan
pom.xml
引入spring-servlet
<dependency>
<groupId>com.whaleson
</groupId>
<artifactId>spring-servlet
</artifactId>
<version>0.0.1-SNAPSHOT
</version>
</dependency>
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<parent>
<artifactId>demo
</artifactId>
<groupId>com.example
</groupId>
<version>0.0.1-SNAPSHOT
</version>
</parent>
<modelVersion>4.0.0
</modelVersion>
<groupId>com.whaleson
</groupId>
<artifactId>spring-boot-servlet
</artifactId>
<dependencies>
<dependency>
<groupId>com.whaleson
</groupId>
<artifactId>spring-servlet
</artifactId>
<version>0.0.1-SNAPSHOT
</version>
</dependency>
<dependency>
<groupId>org.springframework.boot
</groupId>
<artifactId>spring-boot-starter-web
</artifactId>
</dependency>
</dependencies>
</project>
SpringBootServletApplication.java
@EnableAutoConfiguration
public class SpringBootServletApplication {
public static void main(String
[] args
) {
SpringApplication
.run(SpringBootServletApplication
.class,args
);
}
@Bean
@Order(Ordered
.HIGHEST_PRECEDENCE
)
public ServletRegistrationBean
asyncServletRegistrationBean(){
ServletRegistrationBean servletRegistrationBean
= new ServletRegistrationBean(new AsyncServlet(),"/async-servlet");
return servletRegistrationBean
;
}
@Bean
public ServletContextInitializer
servletContextInitializer(){
return servletContext
-> {
CharacterEncodingFilter characterEncodingFilter
= new CharacterEncodingFilter();
FilterRegistration
.Dynamic filterRegistration
= servletContext
.addFilter("filter",characterEncodingFilter
);
filterRegistration
.addMappingForUrlPatterns(EnumSet
.of(DispatcherType
.REQUEST
),false,"/");
};
}
}
@ServletComponentScan
该注解扫描的是spring-servlet模块里AsyncServlet.java所在的包
@Order(Ordered.HIGHEST_PRECEDENCE)
asyncServletRegistrationBean()方法中，该注解添加与否都可以。
浏览器地址
http://localhost:8081/async-servlet
浏览器结果
Hello
控制台结果
当前线程的名称是[http-nio-8081-exec-4]内容是:Hey man. 当前线程的名称是[http-nio-8081-exec-3]内容是:timeout 当前线程的名称是[http-nio-8081-exec-3]内容是:complete
7-16 Spring Boot 嵌入式 Servlet 容器限制 原理分析
通过 RegistrationBean注册
ServletContextInitializer
RegistrationBean
ServletListenerRegistrationBean
@WebListener
FilterRegistrationBean
@WebFilter
ServletRegistrationBean
@WebServlet
@ServletComponentScan扫描 package-> @Web*-> RegistrationBean Bean定义 -> RegistrationBean Bean
7-17 Spring Boot 应用传统 Servlet 容器部署
不支持web.xml部署不支持ServletContainerInitialier接口注解驱动限制
Spring Boot Servlet注册
@Bean方式:RegistrationBean、Servlet组件注解方式:@ServletComponentScan编程方式:ServletContextInitializer
public class DefaultSpringBootServletInitializer extends SpringBootServletInitializer {
protected SpringApplicationBuilder
configure(SpringApplicationBuilder builder
) {
builder
.sources(SpringBootServletApplication
.class);
return builder
;
}
}
