AWS开发工程师错误：发生了JNI错误，... java.lang.NoClassDefFoundError

Question

我正在尝试使用指定的here SDK来完成教程here。

具体来说，我正在尝试使用Maven执行以下Amazon Web Services DynamoDB示例代码：

https://github.com/JohnReedLOL/DynamoDBTutorial/blob/master/src/main/java/org/example/basicapp/MoviesCreateTable.java

像这样...

c4b301bb8ad9:myapp StackOverflowUser$ pwd
/Users/StackOverflowUser/Downloads/apache-maven-3.5.2/bin/myapp

c4b301bb8ad9:myapp StackOverflowUser$ ./../mvn package
[INFO] Scanning for projects...
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] Building myapp 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ myapp ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/StackOverflowUser/Downloads/apache-maven-3.5.2/bin/myapp/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ myapp ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ myapp ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/StackOverflowUser/Downloads/apache-maven-3.5.2/bin/myapp/src/test/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ myapp ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ myapp ---
[INFO] Surefire report directory: /Users/StackOverflowUser/Downloads/apache-maven-3.5.2/bin/myapp/target/surefire-reports

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running org.example.basicapp.AppTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.006 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] 
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ myapp ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.557 s
[INFO] Finished at: 2018-01-20T13:37:59-05:00
[INFO] Final Memory: 12M/225M
[INFO] ------------------------------------------------------------------------

但是当我尝试运行它时，我收到了这个错误......

c4b301bb8ad9:myapp StackOverflowUser$ java -cp target/myapp-1.0-SNAPSHOT.jar org.example.basicapp.MoviesCreateTable
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: com/amazonaws/services/dynamodbv2/document/Table
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
    at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
    at java.lang.Class.getMethod0(Class.java:3018)
    at java.lang.Class.getMethod(Class.java:1784)
    at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
    at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
Caused by: java.lang.ClassNotFoundException: com.amazonaws.services.dynamodbv2.document.Table
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 7 more
c4b301bb8ad9:myapp StackOverflowUser$

我正在运行的Java版本是......

StackOverflowUser$ java -version
java version "1.8.0_151"
Java(TM) SE Runtime Environment (build 1.8.0_151-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.151-b12, mixed mode)

我正在使用此Mac版本运行this jar file ...

我尝试添加到pom.xml：

  <build>
    <plugins>
      <plugin>
        <artifactId>maven-assembly-plugin</artifactId>
        <configuration>
          <archive>
            <manifest>
              <mainClass>org.example.basicapp.MoviesCreateTable</mainClass>
            </manifest>
          </archive>
          <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
        </configuration>
      </plugin>
    </plugins>
  </build>

然后：

$ ./../mvn clean compile assembly:single

但是当我跑步时，我得到了：

$ java -cp target/myapp-1.0-SNAPSHOT.jar org.example.basicapp.MoviesCreateTable
Error: Could not find or load main class org.example.basicapp.MoviesCreateTable

Answer 1

类加载器无法加载要导入的类（com/amazonaws/services/dynamodbv2/document/Table。

您可以通过运行unzip -l myapp-1.0-SNAPSHOT.jar

来证明这一点

它丢失了，因为你的最终jar工件被打包而没有它的依赖（aws-java-sdk）。

请检查是否可以从远程存储库（在本例中为maven central）访问此依赖项，并将其下载到本地.m2存储库。

您可以使用maven-assembly-plugin明确地包含它：

<build>
  <plugins>
    <plugin>
      <artifactId>maven-assembly-plugin</artifactId>
      <configuration>
        <archive>
          <manifest>
            <mainClass>org.example.basicapp.MoviesCreateTable</mainClass>
          </manifest>
        </archive>
        <descriptorRefs>
          <descriptorRef>jar-with-dependencies</descriptorRef>
        </descriptorRefs>
      </configuration>
    </plugin>
  </plugins>
</build>

然后运行mvn clean compile assembly:single打包它。

将创建一个新的jar - myapp-1.0-SNAPSHOT-jar-with-dependencies.jar（与原始jar一起），现在你不必指定主类（你已经在插件配置中做了它并将它设置为你在jar清单上，只需运行java -jar target/myapp-1.0-SNAPSHOT-jar-with-dependencies.jar