Spring Boot应用程序除了生成JAR文件直接运行外，也可以创建成一个WAR文件部署到Web服务器中。在本章节中，我将为你展示如何使用Spring Boot创建WAR文件并在Tomcat Web容器中进行部署。

1. Spring Boot Servlet初始化程序

如果想要在Tomcat Web服务器中部署Spring Boot应用程序，需要让被@SpringBootApplication注解注释的的主类继承SpringBootServletInitializer类，并覆盖configure方法。

下面的代码片段是使用JAR文件运行Spring Boot应用程序的主文件代码：

package com.ramostear.spring.boot.deploytomcat;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

/**
 * @author ramostear
 */
@SpringBootApplication
public class DeployTomcatApplication {

    public static void main(String[] args) {
        SpringApplication.run(DeployTomcatApplication.class, args);
    }

}

现在，我们需要扩展SpringBootServletInlitializer类以支持WAR文件部署。扩展后的主类代码如下：

package com.ramostear.spring.boot.tutorial2;

@SpringBootApplication
public class Application extends SpringBootServletInitializer{
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder){
        return builder.sources(Application.class,args);
    }
    public static void main(String[]args){
        SpringBootApplication.run(Application.class,args);
    }
}

2. 设置主类

对于Spring Boot应用程序，你需要明确的指出在maven构建项目是主类的位置。你需要在pom.xml文件加入如下的代码：

<start-class>com.ramostear.spring.boot.tutorial2.Application</start-class>

3. 更新打包方式

想要将Spring Boot应用程序从jar包更换为war包，还需要修改pom.xml中的packaging配置：

<packaging>war</packaging>

现在，我们可以编写一个简单的REST Endpoint来返回字符串“Hey Spring Boot,I am from tomcat server.”。为了演示此功能，我们还需要将Spring Boot Web Starter添加到pom.xml文件中：

<dependencies>
    ...
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    ...
</dependencies>

接下来，我们将在主类中编写一个简单的REST Endpoint:

package com.ramostear.spring.boot.deploytomcat;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author ramostear
 */
@SpringBootApplication
@RestController
public class DeployTomcatApplication extends SpringBootServletInitializer {

    public static void main(String[] args) {
        SpringApplication.run(DeployTomcatApplication.class, args);
    }

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return builder.sources(DeployTomcatApplication.class);
    }

    @GetMapping("/")
    public String sayHello(){
        return "Hey Spring Boot,I am from tomcat server.";
    }
}

4. 打包Spring Boot应用程序

我们将使用Maven打包命令创建一个可以在Tomcat服务器中运行的WAR文件。使用Maven命令：mvn:package打包应用程序。你可以在当前工程下的target目录中找到war文件：

C:\~projectdir> mvn package

控制台输出：

[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building deploy-tomcat 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-resources-plugin:3.1.0:resources (default-resources) @ deploy-tomcat ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 1 resource
[INFO] Copying 0 resource

.....


[INFO] 
[INFO] --- spring-boot-maven-plugin:2.1.3.RELEASE:repackage (repackage) @ deploy-tomcat ---
[INFO] Replacing main artifact with repackaged archive
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 10.273 s
[INFO] Finished at: 2019-03-04T23:34:12+08:00
[INFO] Final Memory: 38M/288M
[INFO] ------------------------------------------------------------------------

Process finished with exit code 0

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5 . 部署到Tomcat

现在，运行Tomcat服务器，并在webapps目录下部署准备好的war文件。你也可以登录Tomcat的管理界面上传war文件并部署：

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成功部署war文件后，代开浏览器，并在浏览器地址栏输入：http://localhost:8080/deploy-tomcat-0.0.1-SNAPSHOT/ ,观察页面输出结果：

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6 . 主要代码

pom.xml代码：

<?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">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.ramostear</groupId>
    <artifactId>deploy-tomcat</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>deploy-tomcat</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
    <packaging>war</packaging>
</project>

DeployTomcatApplication.java文件：

package com.ramostear.spring.boot.deploytomcat;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author ramostear
 */
@SpringBootApplication
@RestController
public class DeployTomcatApplication extends SpringBootServletInitializer {

    public static void main(String[] args) {
        SpringApplication.run(DeployTomcatApplication.class, args);
    }

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return builder.sources(DeployTomcatApplication.class);
    }

    @GetMapping("/")
    public String sayHello(){
        return "Hey Spring Boot,I am from tomcat server.";
    }
}