最近在學習java agent，需要在生成的jar包裡面的 META-INF/MAINIFEST.MF 必須包含 Premain-Class這個屬性。採用MAVEN的maven-jar-plugin外掛完成。

maven-jar-plugin外掛預設生成的MAINIFEST.MF檔案包含以下幾項：

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Created-By: Apache Maven
Built-By: ${user.name}
Build-Jdk: ${java.version}

現在要新增一個Premain-Class屬性，配置如下：

<plugin>
	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-jar-plugin</artifactId>
	<version>2.3.1</version>
	<configuration>
		<archive>
			<manifest>
				<addClasspath>true</addClasspath>
			</manifest>
			<manifestEntries>
				<Premain-Class>
					com.xzq.test.PreAgent
				</Premain-Class>
			</manifestEntries>
		</archive>
	</configuration>
</plugin>
 

 private void addCustomEntries(Manifest m, Map entries, ManifestConfiguration config)
    throws ManifestException
  {
    addManifestAttribute(m, entries, "Built-By", System.getProperty("user.name"));//設定變數<span style="color:#FF0000;">${user.name}</span>
    addManifestAttribute(m, entries, "Build-Jdk", System.getProperty("java.version"));//設定變數<span style="color:#FF0000;">${java.version}</span>

    if (config.getPackageName() != null)
    {
      addManifestAttribute(m, entries, "Package", config.getPackageName());
    }
  }
 

private void addManifestAttribute(Manifest manifest, Map map, String key, String value)
    throws ManifestException
  {
    if (map.containsKey(key))
    {
      return;
    }
    addManifestAttribute(manifest, key, value);
  }

  private void addManifestAttribute(Manifest manifest, String key, String value)
    throws ManifestException
  {
    if (!StringUtils.isEmpty(value))
    { <span style="color:#FF0000;">//構造自定義屬性</span>
      Manifest.Attribute attr = new Manifest.Attribute(key, value);
      manifest.addConfiguredAttribute(attr);
    }
    else
    {
      Manifest.Attribute attr = new Manifest.Attribute(key, "");
      manifest.addConfiguredAttribute(attr);
    }
  }