Question

尝试运行使用jackon的ObjectMapper类的java程序时出现以下错误：

Exception in thread "main" java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/ObjectMapper
  at com.inin.dynamotransfer.DynamoTransfer.importData(DynamoTransfer.java:133)
  at com.inin.dynamotransfer.DynamoTransfer.main(DynamoTransfer.java:67)
Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.databind.ObjectMapper
  at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
  at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
  ... 2 more

我有Jackson注释，databind（包含ObjectMapper），以及我的Maven存储库中的〜/ .m2 / repository / com / fasterxml / jackson / core / jackson- [packagename] /2.4.0下的核心JAR。这是我的pom.xml的依赖项部分：

<dependencies>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.4.0</version>
    </dependency>

    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.4.0</version>
    </dependency>

    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.4.0</version>
    </dependency>
</dependencies>

这是我的CLASSPATH：

:/Users/myusername/Library/Java/Extensions:/Library/Java/Extensions:/Users/myusername/.m2/repository

所以Maven知道所有这些JAR - 在哪里获取em，在哪里放em等等 - 但java本身似乎无法找到我需要的类。我究竟做错了什么？？谢谢！

Answer 1

尝试重做maven生命周期目标：

mvn clean install -U

Answer 2

默认的maven插件不构建带有依赖项的胖jar。

要构建一个与其依赖项捆绑在一起的jar，以便我们可以使用java -jar执行它，我们可以使用maven-assembly-plugin，它将jar打包为名称xxx-jar-with-dependencies.jar。

以下是pom.xml

示例

<build>
    <plugins>
        <plugin>
            <artifactId>maven-assembly-plugin</artifactId>
            <version>3.0.0</version>
            <configuration>
                <descriptorRefs>
                    <descriptorRef>jar-with-dependencies</descriptorRef>
                </descriptorRefs>
                <archive>
                    <manifest>
                        <mainClass>com.example.yourMain</mainClass>
                    </manifest>
                </archive>
            </configuration>
            <executions>
                <execution>
                    <id>make-assembly</id> <!-- this is used for inheritance merges -->
                    <phase>package</phase> <!-- bind to the packaging phase -->
                    <goals>
                        <goal>single</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

现在你应该能够用

运行你的jar了

java -jar xxx-jar-with-dependencies.jar

java.lang.ClassNotFoundException / NoClassDefFoundError for com / fasterxml / jackson / databind / ObjectMapper with Maven

2 个答案: