springboot-How to solve Error assembling WAR webxml attribute is required exception when building springboot wars

1. The purpose of this post

When build springboot app as war file, sometime we encounter this exception:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-war-plugin:2.2:war (default-war) on project sbjt1: Error assembling WAR: webxml attribute is required (or pre-existing WEB-INF/web.xml if executing in update mode) -> [Help 1]

2. Environments

• springboot 1.x and 2.x

3. The solution

3.1 The original pom

Before solve , we can look at the original pom.xml

<build>
    <finalName>${artifactId}</finalName>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>repackage</goal>
                    </goals>
                    <configuration>
                        <classifier>exec</classifier>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </build>

3.2 The right pom

We should add maven-war-plugin to build springboot as war file:

<build>
    <finalName>${artifactId}</finalName>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>repackage</goal>
                    </goals>
                    <configuration>
                        <classifier>exec</classifier>
                    </configuration>
                </execution>
            </executions>
        </plugin>

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-war-plugin</artifactId>
            <version>3.0.0</version>
        </plugin>
    </plugins>
</build>

And pay attention to the version of the maven-war-plugin, it must be 3.0.0+, or else you must add as follows:

<plugin>
  <artifactId>maven-war-plugin</artifactId>
  <version>2.6</version>
  <configuration>
    <failOnMissingWebXml>false</failOnMissingWebXml>
  </configuration>
</plugin>

Hope it helps for you.