android: FAILURE: Build failed with an exception.

报错1：Could not resolve all files for configuration ':app:debugCompileClasspath'.
> Could not resolve com.android.support:appcompat-v7:29+.
  Required by:
      project :app
   > Failed to list versions for com.android.support:appcompat-v7.
      > Unable to load Maven meta-data from https://dl.google.com/dl/android/maven2/com/android/support/appcompat-v7/maven-metadata.xml.
         > Could not HEAD 'https://dl.google.com/dl/android/maven2/com/android/support/appcompat-v7/maven-metadata.xml'.
            > sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
修改步骤：进入到app的build.greadle中，将第二行原先的'v7:29+'版本改成了'v7:25.3.1'版本，应该只要降低到能匹配的当前gradle和插件的版本就行了。

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:25.3.1'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

报错2：Could not resolve all files for configuration ':app:debugCompileClasspath'.
> Could not download constraint-layout.aar (com.android.support.constraint:constraint-layout:1.1.3)
   > Could not get resource 'https://dl.google.com/dl/android/maven2/com/android/support/constraint/constraint-layout/1.1.3/constraint-layout-1.1.3.aar'.
      > Could not HEAD 'https://dl.google.com/dl/android/maven2/com/android/support/constraint/constraint-layout/1.1.3/constraint-layout-1.1.3.aar'.
         > sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
> Could not download constraint-layout-solver.jar (com.android.support.constraint:constraint-layout-solver:1.1.3)
   > Could not get resource 'https://dl.google.com/dl/android/maven2/com/android/support/constraint/constraint-layout-solver/1.1.3/constraint-layout-solver-1.1.3.jar'.
      > Could not HEAD 'https://dl.google.com/dl/android/maven2/com/android/support/constraint/constraint-layout-solver/1.1.3/constraint-layout-solver-1.1.3.jar'.
         > sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

解决办法来自网络，在app的build.gradle中为buildscript的jcenter指定下载路径。

buildscript {
    
    repositories {
        google()
        jcenter(){ url "http://jcenter.bintray.com/" }
        //加上上面这一个路径/
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.2.0'
        

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

报错3：Execution failed for task ':app:lintVitalRelease'.> Lint found fatal errors while assembling a release target.

    办法来自网络，至于为什么这么配置我也不知道，好几次遇到报错里面有个Lint的都是这么改的；位置依旧是app下的build.gradle。

android {
    compileSdkVersion 25
    buildToolsVersion '28.0.2'
    defaultConfig {
        applicationId "com.example.yonghu.spinner_activity"
        minSdkVersion 21
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
        ///加上如下代码//
        lintOptions {
            checkReleaseBuilds false
            abortOnError false
        }//这里截止了/
    }
}