前言
上一篇文章介绍了SpringBoot的@Conditional的使用和原理，这里在介绍一下EmbeddedServletContainer。
EmbeddedServletContainer是实现内置Web容器的重要实现，这里介绍原理并自定义实现相应的功能。
EmbeddedServletContainer
SpringBoot的Web容器是通过META-INF/spring.factories注入了EmbeddedServletContainerAutoConfiguration。
以tomcat为例，这里判断如果存在Tomcat等类，就会注入TomcatEmbeddedServletContainerFactory，
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(EmbeddedServletContainerCustomizerBeanPostProcessorRegistrar.class)
public class EmbeddedServletContainerAutoConfiguration {
@Configuration
@ConditionalOnClass({ Servlet.class, Tomcat.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedTomcat {
@Bean
public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
return new TomcatEmbeddedServletContainerFactory();
}
}
}
TomcatEmbeddedServletContainerFactory实现了EmbeddedServletContainerFactory
public interface EmbeddedServletContainerFactory {
EmbeddedServletContainer getEmbeddedServletContainer(ServletContextInitializer... initializers);
}
初始化Tomcat并根据ServletContextInitializer对servletContext进行初始化。
public EmbeddedServletContainer getEmbeddedServletContainer(
ServletContextInitializer... initializers) {
Tomcat tomcat = new Tomcat();
File baseDir = (this.baseDirectory != null ? this.baseDirectory
: createTempDir("tomcat"));
tomcat.setBaseDir(baseDir.getAbsolutePath());
Connector connector = new Connector(this.protocol);
tomcat.getService().addConnector(connector);
customizeConnector(connector);
tomcat.setConnector(connector);
tomcat.getHost().setAutoDeploy(false);
tomcat.getEngine().setBackgroundProcessorDelay(-1);
for (Connector additionalConnector : this.additionalTomcatConnectors) {
tomcat.getService().addConnector(additionalConnector);
}
prepareContext(tomcat.getHost(), initializers);
return getTomcatEmbeddedServletContainer(tomcat);
}
EmbeddedServletContainer是具体的Web容器，提供http的服务。
public interface EmbeddedServletContainer {
void start() throws EmbeddedServletContainerException;
void stop() throws EmbeddedServletContainerException;
int getPort();
}
自定义EmbeddedServletContainer
所以自定义需要实现EmbeddedServletContainer和EmbeddedServletContainerFactory两个接口，
另外SpringWeb强依赖ServletContext所以必须自定义一个简单的ServletContext，完整的代码还是放在Github上了。
- 自定义EmbeddedServletContainer，这里使用Java内置的HttpServer提供http服务。
接收到请求后转发给DispatcherServlet进行处理。然后把response转换成HttpServer的输出结果。
public class MyEmbeddedServletContainer implements EmbeddedServletContainer {
private DispatcherServlet dispatcherServlet;
private HttpServer httpServer;
private MyHttpHandler httpHandler;
public MyEmbeddedServletContainer(DispatcherServlet dispatcherServlet) {
this.dispatcherServlet = dispatcherServlet;
this.httpHandler = new MyHttpHandler(dispatcherServlet);
}
public void start() throws EmbeddedServletContainerException {
try {
httpServer = HttpServer.create();
httpServer.bind(new InetSocketAddress("127.0.0.1", getPort()), 0);
httpServer.createContext("/", httpHandler);
httpServer.start();
System.out.println("start http server");
} catch (IOException e) {
e.printStackTrace();
}
}
public void stop() throws EmbeddedServletContainerException {
httpServer.stop(1);
}
public int getPort() {
return 8080;
}
public static class MyHttpHandler implements HttpHandler {
private DispatcherServlet dispatcherServlet;
public MyHttpHandler(DispatcherServlet dispatcherServlet) {
this.dispatcherServlet = dispatcherServlet;
}
public void handle(HttpExchange httpExchange) throws IOException {
MockHttpServletRequest httpServletRequest = new MockHttpServletRequest();
httpServletRequest.setPathInfo(httpExchange.getRequestURI().getPath());
httpServletRequest.setRequestURI(httpExchange.getRequestURI().toString());
MockHttpServletRequest request = new MockHttpServletRequest(httpExchange.getRequestMethod(), httpExchange.getRequestURI().getPath());
MockHttpServletResponse httpServletResponse = new MockHttpServletResponse();
try {
dispatcherServlet.service(request, httpServletResponse);
} catch (ServletException e) {
e.printStackTrace();
}
for (String name : httpServletResponse.getHeaderNames()) {
httpExchange.getResponseHeaders().put(name, httpServletResponse.getHeaders(name));
}
byte[] content = httpServletResponse.getContentAsByteArray();
httpExchange.sendResponseHeaders(200, content.length);
OutputStream outputStream = httpExchange.getResponseBody();
outputStream.write(content);
outputStream.close();
httpExchange.close();
}
}
}
- 自定义EmbeddedServletContainerFactory，注入DispatcherServlet。
因为SpringWeb强依赖ServletContext，所以这里实现了MyMockServletContext继承了MockServletContext，
并简单实现了MockServletContext不支持的功能，具体代码太长了，就不贴了，可以看Github上的完整的代码。
@Configuration
public static class MyEmbeddedServletContainerFactory implements EmbeddedServletContainerFactory {
@Resource
private DispatcherServlet dispatcherServlet;
public EmbeddedServletContainer getEmbeddedServletContainer(ServletContextInitializer... initializers) {
ServletContext servletContext = new MyMockServletContext();
MockServletConfig mockServletConfig = new MockServletConfig();
for (ServletContextInitializer initializer : initializers) {
try {
initializer.onStartup(servletContext);
dispatcherServlet.init(mockServletConfig);
} catch (ServletException e) {
e.printStackTrace();
}
}
return new MyEmbeddedServletContainer(dispatcherServlet);
}
}
public static class MyMockServletContext extends MockServletContext {
......
}
- 程序入口，这里简单定义了一个Controller。
@Configuration
@EnableAutoConfiguration
public class CustomizeServletContainer {
public static void main(String[] args) {
SpringApplication springApplication = new SpringApplication(CustomizeServletContainer.class);
springApplication.run(args);
}
@Controller
public static class MyController {
@RequestMapping("/")
@ResponseBody
public Map index() {
Map msg = new HashMap();
msg.put("hello", "world");
return msg;
}
}
}
运行程序，正常访问就可以输出hello world。
结语
Spring基本覆盖了主流的JavaServlet容器，自己实现就太过复杂了，就没法模拟完整的Servlet的功能，但基本的原理是一致的。