在尝试构建rosjava软件包时，遇到以下错误。
* What went wrong:
Could not resolve all files for configuration ':message_generation:compileClasspath'.
> Could not resolve io.netty:netty:3.5.2.Final.
Required by:
project :message_generation
> Could not resolve io.netty:netty:3.5.2.Final.
> Could not get resource 'https://jcenter.bintray.com/io/netty/netty/3.5.2.Final/netty-3.5.2.Final.pom'.
> Could not GET 'https://jcenter.bintray.com/io/netty/netty/3.5.2.Final/netty-3.5.2.Final.pom'.
> Connect to {proxy IP address removed} [/{proxy IP address removed}] failed: Connect timed out
（已删除IP地址）
我的~/.gradle/gradle.properties如下：
systemProp.http.proxyHost={proxy IP address removed}
systemProp.http.proxyPort=8080
systemProp.http.nonProxyHosts=localhost
systemProp.http.proxyUser=
systemProp.http.proxyPassword=
systemProp.https.proxyHost={proxy IP address removed}
systemProp.https.proxyPort=8080
systemProp.https.nonProxyHosts=localhost
systemProp.https.proxyUser=
systemProp.https.proxyPassword=
IP地址和端口设置正确。代理不使用身份验证。我尝试删除用户名和密码行。
代理本身可以正常工作，我将其用于所有互联网用途。
如何使Gradle正确连接到代理？