通过Java代码获取多个maven模块的类路径

可以使用以下代码，通过Maven API获取多个模块的类路径：

import org.apache.maven.project.MavenProject;
import org.codehaus.plexus.util.DirectoryScanner;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

public class ClasspathUtil {

    public static List<String> getClasspath(List<MavenProject> projects) {
        List<String> classpath = new ArrayList<>();

        for (MavenProject project : projects) {
            classpath.add(project.getBuild().getOutputDirectory());
            classpath.addAll(project.getRuntimeClasspathElements());
        }

        return classpath;
    }

    public static List<File> getClasses(List<MavenProject> projects) {
        List<File> classes = new ArrayList<>();

        for (MavenProject project : projects) {
            DirectoryScanner scanner = new DirectoryScanner();
            scanner.setBasedir(project.getBuild().getOutputDirectory());
            scanner.setIncludes(new String[] { "**/*.class" });
            scanner.scan();
            String[] files = scanner.getIncludedFiles();
            for (String file : files) {
                classes.add(new File(project.getBuild().getOutputDirectory(), file));
            }
        }

        return classes;
    }

}

其中，`getClasspath`方法返回多个模块的类路径列表，`getClasses`方法返回多个模块的所有类文件列表。需要在`pom.xml`中配置`maven-compiler-plugin`插件，如下所示：

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
                <encoding>UTF-8</encoding>
            </configuration>
        </plugin>
    </plugins>
</build>

此外，需要将Maven项目的依赖添加到classpath中，可以使用以下代码：

List<MavenProject> projects = new ArrayList<>();
MavenProject project1 = new MavenProject();
project1.setGroupId("com.example");
project1.setArtifactId("project1");
project1.setVersion("1.0.0");
project1.setDependencies(Arrays.asList(new Dependency[] { new Dependency() {
    {
        setGroupId("com.example");
        setArtifactId("dependency1");
        setVersion("1.0.0");
    }
} }));
projects.add(project1);

List<String> classpath = ClasspathUtil.getClasspath(projects);
for (String path : classpath) {
    URL url = new File(path).toURI().toURL();
    // add url to classpath
}