Flutter调试新项目遇Connection refused错误求助（VS Code/AS）

问题描述 #

已安装Flutter所有依赖项，flutter doctor检测结果全正常，但在VS Code和Android Studio中创建新项目并调试时，出现如下错误：

Launching lib\main.dart on sdk gphone64 x86 64 in debug mode...
lib\main.dart:1
Exception in thread "main" java.net.ConnectException: Connection refused: connect
    at java.base/java.net.PlainSocketImpl.connect0(Native Method)
    at java.base/java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:101)
    at java.base/java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:399)
    at java.base/java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:242)
        at java.base/java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:224)
    at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.base/java.net.Socket.connect(Socket.java:609)
    at java.base/sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:299)
    at java.base/sun.security.ssl.BaseSSLSocketImpl.connect(BaseSSLSocketImpl.java:173)
    at java.base/sun.net.NetworkClient.doConnect(NetworkClient.java:182)
    at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:474)
    at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:569)
        at java.base/sun.net.www.protocol.https.HttpsClient.<init>(HttpsClient.java:266)
    at java.base/sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:373)
    at java.base/sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:203)
    at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1187)
    at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1081)
    at java.base/sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:189)
        at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1592)
    at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1520)
    at java.base/sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:250)
    at org.gradle.wrapper.Download.downloadInternal(Download.java:58)
    at org.gradle.wrapper.Download.download(Download.java:44)
    at org.gradle.wrapper.Install$1.call(Install.java:61)
    at org.gradle.wrapper.Install$1.call(Install.java:48)
        at org.gradle.wrapper.ExclusiveFileAccessManager.access(ExclusiveFileAccessManager.java:65)
    at org.gradle.wrapper.Install.createDist(Install.java:48)
    at org.gradle.wrapper.WrapperExecutor.execute(WrapperExecutor.java:128)
    at org.gradle.wrapper.GradleWrapperMain.main(GradleWrapperMain.java:61)
Exception: Gradle task assembleDebug failed with exit code 1
Exited (sigterm)

预期运行默认Flutter演示代码后，能在模拟器中看到计数递增的应用，但未能实现。

解决方法 #

这个错误核心是Gradle在下载依赖或Wrapper时网络连接失败，以下是针对性的解决步骤：

• 检查网络代理配置
  如果使用了代理，确认代理地址、端口、认证信息正确。同时检查Gradle的代理设置：
  打开项目的android/gradle.properties文件，查看是否有以下配置，确保和当前代理一致，或者暂时注释掉代理配置重试：

  systemProp.http.proxyHost=xxx
  systemProp.http.proxyPort=xxx
  systemProp.https.proxyHost=xxx
  systemProp.https.proxyPort=xxx
  

  也可以执行flutter run -v查看详细日志，定位具体无法连接的URL，手动测试该地址是否能访问。

• 手动下载Gradle Wrapper

  1. 打开项目中gradle/wrapper/gradle-wrapper.properties文件，找到distributionUrl字段，比如https://services.gradle.org/distributions/gradle-7.5-all.zip
  2. 手动下载该Gradle压缩包
  3. 修改distributionUrl为本地文件路径，比如Windows系统：file:///C:/Downloads/gradle-7.5-all.zip，Mac/Linux系统：file:///Users/YourName/Downloads/gradle-7.5-all.zip

• 替换Gradle镜像源
  针对国内网络环境，将Gradle的仓库替换为国内镜像：

  1. 打开项目的android/build.gradle文件，修改buildscript和allprojects下的repositories：

     buildscript {
         repositories {
             maven { url 'https://maven.aliyun.com/repository/google' }
             maven { url 'https://maven.aliyun.com/repository/jcenter' }
             maven { url 'https://maven.aliyun.com/nexus/content/groups/public' }
         }
     }
     
     allprojects {
         repositories {
             maven { url 'https://maven.aliyun.com/repository/google' }
             maven { url 'https://maven.aliyun.com/repository/jcenter' }
             maven { url 'https://maven.aliyun.com/nexus/content/groups/public' }
         }
     }
     

  2. 保存后重新执行flutter run

• 清除缓存重试
  执行以下命令清除Flutter和Gradle缓存：

  flutter clean
  rm -rf .android  # Mac/Linux，Windows用rd /s /q .android
  flutter pub get
  flutter run
  

内容的提问来源于stack exchange，提问作者Atif Shafiq