导出 jar 后出现 NoClassDefFoundError

问题描述

我正在尝试在我的 Java 项目中使用 MongoDB.
将我的项目导出到文件后，我收到 MongoClient 未定义类的错误.
导出时没有出现错误.
我使用 Maven 导入不同的依赖项，并且所有 jars 都正确导出

I am trying to work with MongoDB in my Java projects.
After exporting my project to a file I get a no class defined error for the MongoClient.
I get no errors while exporting.
I use Maven to import the different dependencies and all jars are being exported properly

import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;

public class MongoDB {

    private static MongoClient client;

    public static void init() {
        try {
            client = MongoClients.create("mongodb://localhost:27017/xenoncraft");
            System.out.println("[XenonSuite] Successfully connected to MongoDB");
        } catch(Exception e) {
            System.out.println("[XenonSuite] Following errors were catched while connecting to MongoDB");
            e.printStackTrace();
        }
    }

推荐答案

我是这样解决您的问题的:
结帐项目来自 Github 源代码:
解压、构建、测试
或
1.创建了一个maven项目
mvn archetype:generate -DarchetypeGroupId=org.apache.maven.archetypes -DarchetypeArtifactId=maven-archetype-quickstart -DarchetypeVersion=1.4

This is how I solved your issue:
Checkout project from Github source code:
unzip, build, test
OR
1. Created a maven project
mvn archetype:generate -DarchetypeGroupId=org.apache.maven.archetypes -DarchetypeArtifactId=maven-archetype-quickstart -DarchetypeVersion=1.4

1. 使用以下内容更新 pom.xml，添加来自 OP 的 mongo 客户端代码并打印集合名称
2. 执行mvn clean package
3. 执行java -jar test.jar我得到的输出是:

1. Update pom.xml with following, added mongo client code from OP and printing collection names
2. Executemvn clean package
3. Executejava -jar test.jaroutput I got is:

INFO: Opened connection [connectionId{localValue:1, serverValue:9}] to localhost:27017
Jun 01, 2019 8:17:22 PM com.mongodb.diagnostics.logging.JULLogger log
INFO: Monitor thread successfully connected to server with description ServerDescription{address=localhost:27017, type=STANDALONE, state=CONNECTED, ok=true, version=ServerVersion{versionList=[4, 0, 5]}, minWireVersion=0, maxWireVersion=7, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=2249770}
Jun 01, 2019 8:17:22 PM com.mongodb.diagnostics.logging.JULLogger log
INFO: Opened connection [connectionId{localValue:2, serverValue:10}] to localhost:27017
admin
config
local
test
[XenonSuite] Successfully connected to MongoDB

pom.xml(忽略包名)
检查阴影插件配置

<?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>test</groupId>
  <artifactId>test</artifactId>
  <version>1.0-SNAPSHOT</version>

  <name>test</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <mainClass>test.App</mainClass>
  </properties>

  <packaging>jar</packaging>

  <dependencies>

  <!-- https://mvnrepository.com/artifact/org.mongodb/mongo-java-driver -->
    <dependency>
        <groupId>org.mongodb</groupId>
        <artifactId>mongo-java-driver</artifactId>
        <version>3.10.2</version>
    </dependency>


    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
  </dependencies>

  <build>
      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-assembly-plugin</artifactId>
          <version>3.1.1</version>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-dependency-plugin</artifactId>
          <version>3.1.1</version>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-jar-plugin</artifactId>
          <version>3.1.1</version>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-shade-plugin</artifactId>
          <version>3.2.1</version>
          <executions>
            <execution>
              <phase>package</phase>
              <goals>
                <goal>shade</goal>
              </goals>
              <configuration>
                <shadedArtifactAttached>true</shadedArtifactAttached>
                <transformers>
                  <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                    <mainClass>test.App</mainClass>
                  </transformer>
                </transformers>
                <finalName>test</finalName>
              </configuration>
            </execution>
          </executions>
        </plugin>
      </plugins>
  </build>
</project>

有多种方法可以解决这个问题参考:https://www.baeldung.com/executable-jar-with-maven

There are multiple ways to solve this problemRef: https://www.baeldung.com/executable-jar-with-maven

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