【Azure Developer】记录一次使用Java Azure Key Vault Secret示例代码生成的Jar包，单独运行出现 no main manifest attribute, in target/demo-1.0-SNAPSHOT.jar 错误消息

问题描述

创建一个Java Console程序，用于使用Azure Key Vault Secret。在VS Code中能正常Debug，但是通过mvn clean package打包为jar文件后，使用 java -jar target/demo-1.0-SNAPSHOT.jar 却出现 no main manifest attribute问题。

VS Code中Debug的截图：

java -jar target/demo-1.0-SNAPSHOT.jar 运行错误截图：

PS C:\LBWorkSpace\MyCode\57-KeyVault-java\demo> java -jar target/demo-1.0-SNAPSHOT.jar
no main manifest attribute, in target/demo-1.0-SNAPSHOT.jar

问题解决

问题的原因就是因为通过 mvn package打包的时候，没有添加manifest。可以通过修改 pom.xml文件中的 build 部分的内容，指定mainClass的值为当前项目中main函数所在的位置

  <build>

    <plugins>

      <plugin>

        <groupId>org.apache.maven.plugins</groupId>

        <artifactId>maven-assembly-plugin</artifactId>

        <version>2.5.5</version>

        <configuration>

          <archive>

            <manifest>

              <mainClass>com.example.kvsecretstest.App</mainClass>

            </manifest>

          </archive>

          <descriptorRefs>

            <descriptorRef>jar-with-dependencies</descriptorRef>

          </descriptorRefs>

        </configuration>

      </plugin>

    </plugins>

  </build>

示例中main函数主体：

package com.example.kvsecretstest;

import com.azure.identity.AzureAuthorityHosts;
import com.azure.identity.DefaultAzureCredentialBuilder;

import com.azure.security.keyvault.secrets.SecretClient;
import com.azure.security.keyvault.secrets.SecretClientBuilder;
import com.azure.security.keyvault.secrets.models.KeyVaultSecret;

/**
 * Hello world!
 *
 */
public class App {
        public static void main(String[] args) throws InterruptedException {
                System.out.println("Hello World!");

                String keyVaultUri = "https://xxxxxxxxxxxxx.vault.azure.cn/";

                System.out.printf("key vault name = xxxxxxxxx and key vault URI = %s \n", keyVaultUri);

                String userIdentityID = "xxxxxxxxxxxxxxxxxxxxxxxxxx";
                SecretClient secretClientidentity = new SecretClientBuilder()
                                .vaultUrl(keyVaultUri)
                                .credential(new DefaultAzureCredentialBuilder().managedIdentityClientId(userIdentityID)
                                                .authorityHost(AzureAuthorityHosts.AZURE_CHINA)
                                                .build())
                                .buildClient();

                String secretName = "ExamplePassword";

                KeyVaultSecret retrievedSecret = secretClientidentity.getSecret(secretName);

                System.out.println("Your secret's value is '" + retrievedSecret.getValue() + "'.");

                System.out.println("done.");
        }

}

修改完POM.XML文件后，先mvn clean清理所有已经生成的target文件。

然后使用新的打包命令: mvn package assembly:single， 生成一个包含所有依赖项目的jar包。

然后通过java -jar 命令运行 java -jar target\demo-1.0-SNAPSHOT-jar-with-dependencies.jar

运行成功，解决no main manifest attribute 问题！

附录一：完整版的Pom.xml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>com.example.kvsecretstest</groupId>
  <artifactId>demo</artifactId>
  <version>1.0-SNAPSHOT</version>

  <name>demo</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>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>com.azure</groupId>
      <artifactId>azure-security-keyvault-secrets</artifactId>
      <version>4.2.3</version>
    </dependency>

    <dependency>
      <groupId>com.azure</groupId>
      <artifactId>azure-identity</artifactId>
      <version>1.2.0</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-assembly-plugin</artifactId>
        <version>2.5.5</version>
        <configuration>
          <archive>
            <manifest>
              <mainClass>com.example.kvsecretstest.App</mainClass>
            </manifest>
          </archive>
          <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

参考资料

适用于 Java 的 Azure Key Vault 机密客户端库：https://docs.azure.cn/zh-cn/key-vault/secrets/quick-create-java?tabs=azure-cli

Maven生成可以直接运行的jar包的多种方式：https://xxgblog.com/2015/08/07/maven-create-executable-jar/

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