嵌入式 Tomcat 作为嵌入 Java 应用程序的库, 你可以在 mvnrepository 下载 发行版Jar 以及源码

https://mvnrepository.com/search?q=embed+tomcat

作为最基本的依赖, 你需要以下几个库

• Tomcat Embed Core
• Tomcat Embed Logging JULI
• Tomcat Annotations API

现在, 让我们把 tomcat 跑起来

package develon.test;import java.io.File;
import java.io.IOException;
import java.io.Writer;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import org.apache.catalina.Context;
import org.apache.catalina.LifecycleException;
import org.apache.catalina.connector.Connector;
import org.apache.catalina.startup.Tomcat;public final class Main {File tmpDir = new File("F:\\Game\\tomcat");Tomcat tomcat = new Tomcat();public static void main(String[] args) throws Throwable {new Main().init();}private void init() throws Throwable {Runtime.getRuntime().addShutdownHook(new Thread(() -> {try {tomcat.destroy();} catch (LifecycleException e) {e.printStackTrace();}}));test();}private void test() throws Throwable {tomcat.setBaseDir(tmpDir.getAbsolutePath()); // 设置工作目录tomcat.setHostname("localhost"); // 主机名, 将生成目录: {工作目录}/work/Tomcat/{主机名}/ROOTSystem.out.println("工作目录: " + tomcat.getServer().getCatalinaBase().getAbsolutePath());tomcat.setPort(80);Connector conn = tomcat.getConnector(); // Tomcat 9.0 必须调用 Tomcat#getConnector() 方法之后才会监听端口System.out.println("连接器设置完成: " + conn);// contextPath要使用的上下文映射，""表示根上下文// docBase上下文的基础目录，用于静态文件。相对于服务器主目录必须存在 ({主目录}/webapps/{docBase})Context ctx = tomcat.addContext("", /*{webapps}/~*/ "/ROOT");Tomcat.addServlet(ctx, "globalServlet", new HttpServlet() {private static final long serialVersionUID = 1L;@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setCharacterEncoding("UTF-8");response.setContentType("text/plain");response.setHeader("Server", "Embedded Tomcat");try (Writer writer = response.getWriter()) {writer.write("Hello, Embedded Tomcat!");writer.flush();}}});ctx.addServletMappingDecoded("/", "globalServlet");tomcat.start();System.out.println("tomcat 已启动");tomcat.getServer().await();}}

tomcat 嵌入正常, 让我们继续, 如何令 tomcat 加载 Spring Framework ?

嵌入式 tomcat 集成 Spring 框架

package develon.tomc;import java.util.HashSet;import org.apache.catalina.Context;
import org.apache.catalina.LifecycleEvent;
import org.apache.catalina.LifecycleListener;
import org.apache.catalina.LifecycleState;
import org.apache.catalina.startup.Tomcat;
import org.springframework.web.SpringServletContainerInitializer;public class Main {Tomcat tomcat;{tomcat = new Tomcat();
//      tomcat.setAddDefaultWebXmlToWebapp(false);
//      tomcat.noDefaultWebXmlPath();}public void run() throws Throwable {tomcat.setBaseDir("F:\\Game\\tomcat");tomcat.setHostname("localhost");tomcat.setPort(80);
//      tomcat.enableNaming();//      tomcat.getHost().setAutoDeploy(false);
//      tomcat.getEngine().setBackgroundProcessorDelay(-1);Context ctx = tomcat.addContext("", "ROOT");ctx.addLifecycleListener(new LifecycleListener() {public void lifecycleEvent(LifecycleEvent event) {
//              System.out.println(event.getLifecycle().getState().name());if (event.getLifecycle().getState() == LifecycleState.STARTING_PREP) {try {new SpringServletContainerInitializer().onStartup(new HashSet<Class<?>>() {private static final long serialVersionUID = 1L;{add(WebAppInitializer.class);}}, ctx.getServletContext());} catch (Throwable e) {e.printStackTrace();}}}});//      tomcat.init();tomcat.getConnector();tomcat.start();tomcat.getServer().await();}public static void main(String[] args) throws Throwable {new Main().run();}
}

其中 WebAppInitializer 是继承 AbstractAnnotationConfigDispatcherServletInitializer 的一个配置类
由于 AbstractAnnotationConfigDispatcherServletInitializer 继承了 SpringServletContainerInitializer, 所以可以简写为

        Context ctx = tomcat.addContext("", "ROOT");ctx.addLifecycleListener(new LifecycleListener() {public void lifecycleEvent(LifecycleEvent event) {if (event.getLifecycle().getState() == LifecycleState.STARTING_PREP) {try {new WebAppInitializer().onStartup(ctx.getServletContext());} catch (Throwable e) {e.printStackTrace();}}}});

这种方式好像会报一个错误, 不过可以忽略它, 但是注意这是一个运行时异常, 我们最好捕获 Throwable, 否则程序直接退出了
(经查, 是由于注射 dispacherServlet 两次造成的, 实际上第一次已经注射完成了)

java.lang.IllegalStateException: Failed to register servlet with name 'dispatcher'. Check if there is another servlet registered under the same name.at org.springframework.web.servlet.support.AbstractDispatcherServletInitializer.registerDispatcherServlet(AbstractDispatcherServletInitializer.java:90)at org.springframework.web.servlet.support.AbstractDispatcherServletInitializer.onStartup(AbstractDispatcherServletInitializer.java:63)at develon.tomc.Main$1.lifecycleEvent(Main.java:37)

然后我们还能用闭包进一步简化程序, 并且把烦人的栈痕迹删除

        ctx.addLifecycleListener((LifecycleEvent event) -> {if (event.getLifecycle().getState() == LifecycleState.STARTING_PREP) {try {new WebAppInitializer().onStartup(ctx.getServletContext());} catch (Throwable e) {
//                  e.printStackTrace();}}});

我用 kotlin 简单地封装了一个 EmbeddedTomcat 类

import org.apache.catalina.startup.Tomcat
import org.apache.catalina.Context
import org.apache.catalina.LifecycleStateclass EmbeddedTomcat {var tomcat: Tomcat = Tomcat()var ctx: Context? = nullinit {}/** 初始化嵌入式 tomcat */fun init() {tomcat.setBaseDir("""F:\\Game\\tomcat""")tomcat.setHostname("localhost")tomcat.setPort(80)ctx = tomcat.addContext("", "ROOT")}/** 开始监听服务 */fun run() {tomcat.getConnector()tomcat.start()tomcat.getServer().await()}/** 启动 Spring 框架, 注射 DispatcherServlet */fun spring() {var tyusya = falsectx?.addLifecycleListener {if (tyusya == false && it.getLifecycle().getState() == LifecycleState.STARTING_PREP) {println("开始注射 -> ${ it.getLifecycle().getState() }")val sctx = ctx?.getServletContext()try {WebAppInitializer().onStartup(sctx)println("完成")tyusya = true} catch(e: Throwable) {println("失败: ${ e.message }")}}}}fun spring2() { // 调用了 removeLifecycleListener 移除 tomcat 生命周期监听器ctx?.addLifecycleListener(object : LifecycleListener {override fun lifecycleEvent(it: LifecycleEvent) {if (it.getLifecycle().getState() == LifecycleState.STARTING_PREP) {println("开始注射 DispatcherServlet -> ${ it.getLifecycle().getState() }")try {WebAppInitializer().onStartup(ctx?.getServletContext())println("注射完成")ctx?.removeLifecycleListener(this)} catch(e: Throwable) {println("注射失败: ${ e.message }")}}}})}
}fun main() {val tomcat = EmbeddedTomcat()tomcat.init()tomcat.spring()tomcat.run()
}

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer
import org.springframework.context.annotation.ComponentScan@ComponentScan(basePackageClasses = [DefController::class])
class WebAppInitializer : AbstractAnnotationConfigDispatcherServletInitializer() {override fun getRootConfigClasses() = nulloverride fun getServletMappings() = arrayOf("/")override fun getServletConfigClasses() = arrayOf(WebAppInitializer::class.java)
}