无法将数据写入Firebase实时数据库

Question

我正在做firebase的工作，但是无法连接到实时数据库。我得到了以下错误。当我按下“工具”菜单中的“连接到火基”按钮时，它显示您已经连接了。以下是所有类的主类

package com.example.mall_parking_app;

import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

public class System {
    member member;
    parkDirection parkDirection;
    shoppingCenter shoppingCenter;

    public static void main(String[]args) {
        // Write a message to the database
        FirebaseDatabase database;
        database = FirebaseDatabase.getInstance();
        DatabaseReference myRef = database.getReference("message");
        myRef.setValue("Hello, World!");

构建爷爷:app

    plugins {
    id 'com.android.application'
    id 'com.google.gms.google-services'
}
apply plugin: 'com.android.application'
apply plugin: 'com.google.gms.google-services'
android {
    compileSdk 31

    defaultConfig {
        configurations.all {
            resolutionStrategy { force 'androidx.core:core:1.6.0' }
        }
        applicationId "com.example.mall_parking_app"
        minSdk 30
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    buildToolsVersion '30.0.3'
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.4.1'
    implementation 'com.google.android.material:material:1.5.0'
    implementation 'com.google.firebase:firebase-database:20.0.4'
    implementation 'com.google.firebase:firebase-storage:20.0.1'
    implementation 'com.google.firebase:firebase-config:21.0.2'
    implementation 'com.google.firebase:firebase-dynamic-links:21.0.1'
    implementation 'com.google.firebase:firebase-messaging:23.0.2'
    implementation 'com.google.firebase:firebase-auth:21.0.2'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}
dependencies {
    // Import the BoM for the Firebase platform
    implementation platform('com.google.firebase:firebase-bom:29.3.0')

    implementation 'com.google.firebase:firebase-analytics'
    // Declare the dependency for the Realtime Database library
    // When using the BoM, you don't specify versions in Firebase library dependencies
    implementation 'com.google.firebase:firebase-database:20.0.4'
}
dependencies {
    implementation 'com.google.zxing:core:3.4.1'
    implementation 'com.google.zxing:javase:3.4.1'
}
dependencies {
    implementation 'com.google.firebase:firebase-appcheck-debug:16.0.0'
}

当我运行时出错

Exception in thread "main" java.lang.NoClassDefFoundError: com/google/firebase/database/FirebaseDatabase
    at com.example.mall_parking_app.System.main(System.java:15)
Caused by: java.lang.ClassNotFoundException: com.google.firebase.database.FirebaseDatabase
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
    ... 1 more

实时数据库规则

{
  "rules": {
    ".read": true,
    ".write": true
  }
}

我怎么能解决这个问题？

Answer 1

您应该使用.getReference("/message")而不是.getReference("message")。