用 idea 写 gradle 项目， ide 找不到依赖

写了个 demo ，引了个 okhttp 的依赖，但 ide 里面老是红色报错说找不到，但 gradle build 却可以通过。好烦啊 o(>< )o 什么提示都没有还不如记事本，不知道该怎么解决。

项目有两个子项目

root
|— backend
|— front

root 的 builde.gradle

buildscript {
    ext {
        springBootVersion = '1.4.0.RELEASE'
    }
    repositories {
        jcenter()
        maven { url "http://repo.spring.io/snapshot" }
        maven { url "http://repo.spring.io/milestone" }
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
    }
}

subprojects {
    apply plugin: 'spring-boot'
    apply plugin: 'java'
    apply plugin: 'eclipse'
    apply plugin: 'idea'

    repositories {
        jcenter()
        maven { url "http://repo.spring.io/snapshot" }
        maven { url "http://repo.spring.io/milestone" }
        mavenCentral()
    }

    dependencies {
        testCompile 'junit:junit:4.12'
        compile('org.springframework.boot:spring-boot-starter')
        compile("org.springframework.boot:spring-boot-starter-web")
        compile 'com.squareup.okhttp3:okhttp:3.4.1'
        compile 'org.mousio:etcd4j:2.12.0'
        testCompile('org.springframework.boot:spring-boot-starter-test')
    }

    version = '1.0'

    jar {
        manifest.attributes provider: 'gradle'
    }

}

子项目的 build.gradle

sourceCompatibility = 1.8
targetCompatibility = 1.8

jar {
	baseName = 'front'
	version = '0.0.1-SNAPSHOT'
}

eclipse {
	classpath {
		 containers.remove('org.eclipse.jdt.launching.JRE_CONTAINER')
		 containers 'org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8'
	}
}