Question

我正在尝试使用Maven的jackson databind。它在我的IDE环境中运行正常（我正在使用IntelliJ IDEA），但是当我尝试用它制作一个jar时，它会在启动时产生错误并立即崩溃。具体来说，错误是这样的：

java.lang.NoClassDefFoundError: com/fasterxml/jackson/core/JsonFactory

这是JAR特有的，我不知道为什么会这样做。我做错了什么？

这是pom文件：

<?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>

    <groupId>me.zam</groupId>
    <artifactId>jackson</artifactId>
    <version>1.0-SNAPSHOT</version>

    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.2.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.dataformat</groupId>
            <artifactId>jackson-dataformat-yaml</artifactId>
            <version>2.3.0</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <!-- Make this jar executable -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <configuration>
                    <archive>
                        <manifest>
                            <!-- Jar file entry point -->
                            <mainClass>me.Main</mainClass>
                            <addClasspath>true</addClasspath>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

这是主要对象

package me;

import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;

/**
 * Created by Martin on 31/03/2017.
 */
public class Main
{
    public static void main(String[] args)
    {
        ObjectMapper mapper = new ObjectMapper(new YAMLFactory());
        try {
            User user = mapper.readValue(new File("user.yaml"), User.class);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

Answer 1

所以我只是在我的系统中尝试过并且能够模拟这个问题。

要解决此问题，您需要再添加一个插件maven-shade-plugin，这是创建胖罐所必需的，即。具有所有必需依赖性的jar。

更新pom.xml文件，请注意我已将包含main方法的类重命名为Test并放入默认包中： -

<?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>

    <groupId>com.so</groupId>
    <artifactId>jackson</artifactId>
    <version>1.0-SNAPSHOT</version>

    <packaging>jar</packaging>

    <properties>
        <mainClass>Test</mainClass>
    </properties>

    <dependencies>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.2.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.dataformat</groupId>
            <artifactId>jackson-dataformat-yaml</artifactId>
            <version>2.3.0</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.4.1</version>
                <configuration>
                    <createDependencyReducedPom>true</createDependencyReducedPom>
                    <transformers>
                        <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
                        <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                            <mainClass>${mainClass}</mainClass>
                        </transformer>
                    </transformers>
                    <!-- exclude signed Manifests -->
                    <filters>
                        <filter>
                            <artifact>*:*</artifact>
                            <excludes>
                                <exclude>META-INF/*.SF</exclude>
                                <exclude>META-INF/*.DSA</exclude>
                                <exclude>META-INF/*.RSA</exclude>
                            </excludes>
                        </filter>
                    </filters>
                </configuration>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <!-- Make this jar executable -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <configuration>
                    <archive>
                        <manifest>
                            <!-- Jar file entry point -->
                            <mainClass>Test</mainClass>
                            <addClasspath>true</addClasspath>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

完成后，我通过运行首先运行mvn clean package命令来运行代码，该命令创建胖jar，然后通过java -cp target/jackson-1.0-SNAPSHOT.jar Test命令运行代码。

如果您在运行代码时遇到任何问题，请与我们联系。

Answer 2

您能否检查生成的jar是否包含指定的依赖项，例如jackson-databind和jackson-dataformat-yaml？我不确定jar插件是否导出了maven依赖项。我通常使用maven程序集插件或者插件来生成带有依赖关系的jar。

Answer 3

我不确定，但您需要将<mainClass>更改为<MainClass>，并将依赖项的范围设置为<scope>compile</scope>，以将其直接添加到jar文件中。

Jackson databind在IDE环境中工作但不在jar中工作

3 个答案: