以编程方式创建 Fat-Jar

Question

我正在尝试以编程方式创建一个fat-jar。到目前为止，我成功创建了一个包含我的代码的 Jar 文件。问题是，如果我运行这个，我会收到一个异常，说

Cannot load user class: org.company.bla.bla

。

这是我的代码

    private static void createJar() throws IOException {

        Manifest manifest = new Manifest();
        manifest.getMainAttributes().put(Attributes.Name.MANIFEST_VERSION, "1.0");
        JarOutputStream target = new JarOutputStream(new FileOutputStream("events.jar"), manifest);

        Path root = Paths.get(".").normalize().toAbsolutePath();
        System.out.println(root.toString());

        Files.walk(root).forEach(f -> add(f.toFile(), target));

        target.close();
    }

    private static void add(File source, JarOutputStream target)
    {
        BufferedInputStream in = null;
        try {
            if (source.isDirectory()) {
                String name = source.getPath().replace("\\", "/");
                if (!name.isEmpty()) {
                    if (!name.endsWith("/"))
                        name += "/";
                    JarEntry entry = new JarEntry(name);
                    entry.setTime(source.lastModified());
                    target.putNextEntry(entry);
                    target.closeEntry();
                }
                for (File nestedFile: source.listFiles())
                    add(nestedFile, target);
                return;
            }

            JarEntry entry = new JarEntry(source.getPath().replace("\\", "/"));
            entry.setTime(source.lastModified());
            target.putNextEntry(entry);
            in = new BufferedInputStream(new FileInputStream(source));

            byte[] buffer = new byte[1024];
            while (true) {
                int count = in.read(buffer);
                if (count == -1)
                    break;
                target.write(buffer, 0, count);
            }
            target.closeEntry();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

我怎样才能将依赖项添加到这个 Jar 中？或者依赖项所在的路径在哪里，以便我可以包含它们？

Answer 1

创建 Uber / Shadow JAR 意味着 Maven 或 Gradle 也用于处理所有库依赖项。

如果是这样，一种解决方案是从 Java 运行 Maven 或 Gradle 构建命令行参数（使用

Runtime.exec()

命令）。

以编程方式执行此操作的用例是作为 Java 集成测试的一部分，其中需要 Uber Jar（有关示例，请参阅使用测试容器测试自定义 Kafka Connect SMT）。

以下解决方案同时支持 Gradle / Maven。

Maven

确保

pom.xml

包含 Maven Shade Plugin 插件，例如

<?xml version="1.0" encoding="UTF-8"?>
<project>
    <modelVersion>4.0.0</modelVersion>

    <groupId>test</groupId>
    <artifactId>helloworld</artifactId>
    <version>1.0</version>
    <packaging>jar</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <jdk.version>1.11</jdk.version>
        <maven.compiler.plugin.version>3.8.1</maven.compiler.plugin.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.13.0</version>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>5.8.0</version>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.8.0</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.5.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

在项目上安装 Maven 包装器 也很有用（只需运行

mvn wrapper:wrapper

）。

摇篮

对于 Gradle，我们应该确保 Gradle Shadow 插件存在于

plugins

文件的

build.gradle

部分，例如

plugins {
    id("com.github.johnrengelman.shadow") version "6.0.0"
}

apply plugin: 'java'

java {
    sourceCompatibility = 1.11
    targetCompatibility = 1.11
}

repositories {
    mavenCentral()
}

test {
    useJUnitPlatform()
}

dependencies {
    implementation 'org.apache.commons:commons-lang3:3.13.0'

    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.8.0'
    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.8.0'
}

创建 UberJars 的代码如下：

public class UberJar {

    public static void createUberJarMaven() {
        createUberJar("mvnw.cmd", "./mvnw", "package -DskipTests", "BUILD SUCCESS");
    }

    public static void createUberJarGradle() {
        createUberJar("gradlew.bat", "./gradlew", "shadowJar", "BUILD SUCCESSFUL");
    }

    private static void createUberJar(String cmdWindows, String cmdLinux, String cmdBuild, String outputSuccess) {
        String cmd = isWindows() ? cmdWindows : cmdLinux;
        String output = execCmd(cmd + " " + cmdBuild);
        if (output == null || !output.contains(outputSuccess)) {
            throw new RuntimeException("Ubar JAR creation unsuccessful\n\n" + output);
        }
    }

    private static String execCmd(String cmd) {
        try {
            Scanner s = new Scanner(Runtime.getRuntime().exec(cmd).getInputStream()).useDelimiter("\\A");
            return s.hasNext() ? s.next() : "";
        } catch (IOException ioEx) {
            throw new RuntimeException("Error executing: " + cmd, ioEx);
        }
    }

    private static boolean isWindows() {
        return System.getProperty("os.name").toLowerCase().startsWith("windows");
    }

}

测试这两者的单元测试如下：

public class UbarJarTest {

    @Test
    public void should_create_uber_jar_maven() {
        UberJar.createUberJarMaven();
    }

    @Test
    public void should_create_uber_jar_gradle() {
        UberJar.createUberJarGradle();
    }
    
}