Google app engine Android Studio GAE项目部署：类文件是Java8，但支持的最大值是Java7

我在安卓工作室有一个谷歌应用引擎项目。在过去，我曾多次成功地将其部署到我的项目中，以实现GAE。但是，某些项目设置已更改，我无法再部署。我得到的信息是：

java.lang.IllegalArgumentException: Class file is Java 8 but max supported is Java 7: javax/ws/rs/ApplicationPath.class in /Users/rob/AndroidStudioProjects/SpeedyMovingInventory/backend/build/exploded-app/WEB-INF/lib/javax.ws.rs-api-2.1-m02.jar
Unable to update app: Class file is Java 8 but max supported is Java 7: javax/ws/rs/ApplicationPath.class in /Users/rob/AndroidStudioProjects/SpeedyMovingInventory/backend/build/exploded-app/WEB-INF/lib/javax.ws.rs-api-2.1-m02.jar
Please see the logs [/var/folders/cn/3ktx4pj50hs7338v88b0sckh0000gn/T/appcfg3087406806803083082.log] for further information.

我已尝试在我的build.gradle中设置源和目标兼容性，如下所示：

// If you would like more information on the gradle-appengine-plugin please refer to the github page
// https://github.com/GoogleCloudPlatform/gradle-appengine-plugin

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.google.appengine:gradle-appengine-plugin:1.9.34'
    }
}

repositories {
    jcenter();
}

apply plugin: 'java'
apply plugin: 'war'
apply plugin: 'appengine'

sourceCompatibility = JavaVersion.VERSION_1_7
targetCompatibility = JavaVersion.VERSION_1_7

dependencies {

    appengineSdk 'com.google.appengine:appengine-java-sdk:1.9.34'
    compile 'javax.servlet:servlet-api:2.5'
    compile 'com.google.appengine:appengine-api-1.0-sdk:1.9.34'
    compile 'joda-time:joda-time:2.8.2'
    compile 'net.sargue:mailgun:1.0.0'
    compile 'com.google.code.gson:gson:2.7'
    testCompile 'junit:junit:4.12'
    testCompile 'org.mockito:mockito-core:1.10.19'
    // Set this dependency if you want to use Hamcrest matching
    testCompile 'org.hamcrest:hamcrest-library:1.1'
    testCompile fileTree(include: ['*.jar'], dir: '/Users/rob/appengine-java-sdk-1.9.34/lib/impl')
    testCompile fileTree(include: ['*.jar'], dir: '/Users/rob/appengine-java-sdk-1.9.34/lib/testing')
}


appengine {
    downloadSdk = true
    appcfg {
        oauth2 = true
    }

}

---

我还使用androidstudio生成了一个示例GAE模块，并成功地将该示例部署到GAE。我比较了gradle文件和设置，没有发现任何差异。请帮忙，我做错了什么？

经过大量研究，我找到了解决办法。库'net.sargue:mailgun:1.0.0'显然在某种程度上依赖于Java8库（或者类似的库）。我不知道为什么这在过去没有给我带来麻烦，但现在是了。将库升级到“net.sargue:mailgun:1.3.2”解决了这个问题。

我与mailgun库的作者进行了一次对话：

他有一个被更新为Java8的依赖项，他在新版本中修复了它