1.下载源码

wget https://repo1.maven.org/maven2/org/apache/tomcat/embed/tomcat-embed-core/9.0.43/tomcat-embed-core-9.0.43-sources.jar -O tomcat-embed-core-9.0.43-sources.jar

2.新建maven工程

3.解压tomcat-embed-core-9.0.43-sources.jar并将源码拷贝到项目中
4.修改pom.xml

<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>
    <groupId>org.apache.tomcat.embed</groupId>
    <artifactId>tomcat-embed-core</artifactId>
    <version>9.0.43</version>
    <description>Core Tomcat implementation</description>
    <url>http://tomcat.apache.org/</url>
    <properties>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

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

    <dependencies>

        <dependency>
            <groupId>biz.aQute.bnd</groupId>
            <artifactId>biz.aQute.bndlib</artifactId>
            <version>5.2.0</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>javax.mail</groupId>
            <artifactId>javax.mail-api</artifactId>
            <version>1.6.2</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>wsdl4j</groupId>
            <artifactId>wsdl4j</artifactId>
            <version>1.6.3</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.apache.geronimo.specs</groupId>
            <artifactId>geronimo-jaxrpc_1.1_spec</artifactId>
            <version>2.1</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.glassfish</groupId>
            <artifactId>javax.ejb</artifactId>
            <version>3.1.1</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>javax.persistence</groupId>
            <artifactId>javax.persistence-api</artifactId>
            <version>2.2</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>