Android连接远程数据库的避坑指南

今天用Android Studio连接数据库时候，写了个测试连接的按钮，然后连接的时候报错了，报错信息：

2021-09-07 22:45:20.433 7054-7083/cn.xuziao.faceprocess E/AndroidRuntime: FATAL EXCEPTION: Thread-113

    Process: cn.xuziao.faceprocess, PID: 7054

    java.lang.NoSuchMethodError: No virtual method group(Ljava/lang/String;)Ljava/lang/String; in class Ljava/util/regex/Matcher; or its super classes (declaration of 'java.util.regex.Matcher' appears in /system/framework/core-libart.jar)

        at com.mysql.cj.conf.ConnectionUrlParser.isConnectionStringSupported(ConnectionUrlParser.java:152)

        at com.mysql.cj.conf.ConnectionUrl.acceptsUrl(ConnectionUrl.java:317)

        at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:186)

        at java.sql.DriverManager.getConnection(DriverManager.java:179)

        at java.sql.DriverManager.getConnection(DriverManager.java:213)

        at cn.xuziao.faceprocess.LoginActivity$1$1.run(LoginActivity.java:38)

        at java.lang.Thread.run(Thread.java:818)

然后我当时写的按钮点击执行方法片段

textView.setOnClickListener(new View.OnClickListener() {

    @Override

    public void onClick(View v) {

        try {

            Class.forName("com.mysql.jdbc.Driver");

            String url = "jdbc:mysql://172.17.9.241:3306/user_info";

            String login_username = "login";

            String login_password = "root";

            Connection connection = DriverManager.getConnection(url, login_username, login_password);

            String sql = "select username from base_info";

            Statement statement = connection.createStatement();

            ResultSet resultSet = statement.executeQuery(sql);

            while (resultSet.next()){

                Log.d(TAG, resultSet.getString(1));

            }

        } catch (ClassNotFoundException | SQLException e) {

            e.printStackTrace();

        }

        Toast.makeText(LoginActivity.this, "注册中...", Toast.LENGTH_SHORT).show();

    }

});

附上当时的build.gradle文件里面我导入的依赖

dependencies {

    implementation 'androidx.appcompat:appcompat:1.2.0'

    implementation 'com.google.android.material:material:1.3.0'

    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'

    testImplementation 'junit:junit:4.+'

    androidTestImplementation 'androidx.test.ext:junit:1.1.2'

    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'

    implementation 'mysql:mysql-connector-java:8.0.26'

}

最后一行是我引入的依赖

然后我就查到，安卓的主线程不能访问网络，具体博客：https://www.cnblogs.com/lyroge/p/3837902.html

引入后的代码：

textView.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                new Thread(new Runnable() {

                    @Override

                    public void run() {

                        try {

                            Class.forName("com.mysql.jdbc.Driver");

                            String url = "jdbc:mysql://172.17.9.241:3306/user_info";

                            String login_username = "login";

                            String login_password = "root";

                            Connection connection = DriverManager.getConnection(url, login_username, login_password);

                            String sql = "select username from base_info";

                            Statement statement = connection.createStatement();

                            ResultSet resultSet = statement.executeQuery(sql);

                            while (resultSet.next()){

                                Log.d(TAG, resultSet.getString(1));

                            }

                        } catch (ClassNotFoundException | SQLException e) {

                            e.printStackTrace();

                        }

                    }

                }).start();

                Toast.makeText(LoginActivity.this, "注册中...", Toast.LENGTH_SHORT).show();

            }

        });

然后我引入了多线程，还是报错，报错信息跟上面是一样的，那就说明问题不只主线程不能访问网络的问题，然后我就改了好久奇奇怪怪的东西，我就看到我的安卓自带的jdk版本是1.8但是我的MySQL驱动到了8，然后我就去把MySQL驱动换成了5,build.gradle依赖部分改为：

dependencies {

    implementation 'androidx.appcompat:appcompat:1.2.0'

    implementation 'com.google.android.material:material:1.3.0'

    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'

    testImplementation 'junit:junit:4.+'

    androidTestImplementation 'androidx.test.ext:junit:1.1.2'

    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'

    implementation 'mysql:mysql-connector-java:5.1.6'

}

然后我发现上面那个报错的问题解决了，然后报了新的错：

W/System.err: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

    Last packet sent to the server was 0 ms ago.

        at java.lang.reflect.Constructor.newInstance(Native Method)

        at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)

        at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)

        at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2103)

        at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:718)

        at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)

        at java.lang.reflect.Constructor.newInstance(Native Method)

        at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)

        at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)

        at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)

        at java.sql.DriverManager.getConnection(DriverManager.java:179)

        at java.sql.DriverManager.getConnection(DriverManager.java:213)

        at cn.xuziao.faceprocess.LoginActivity$1$1.run(LoginActivity.java:37)

        at java.lang.Thread.run(Thread.java:818)

    Caused by: java.net.UnknownHostException: Unable to resolve host "172.17.9.241": No address associated with hostname

        at java.net.InetAddress.lookupHostByName(InetAddress.java:470)

        at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252)

        at java.net.InetAddress.getAllByName(InetAddress.java:215)

        at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:243)

        at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:280)

        at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2026)

    	... 10 more

W/System.err: Caused by: android.system.GaiException: android_getaddrinfo failed: EAI_NODATA (No address associated with hostname)

        at libcore.io.Posix.android_getaddrinfo(Native Method)

        at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:55)

        at java.net.InetAddress.lookupHostByName(InetAddress.java:451)

    	... 15 more

    Caused by: android.system.ErrnoException: android_getaddrinfo failed: ECONNREFUSED (Connection refused)

    	... 18 more

这个错是被异常捕获机制捕获到的一个错误，说明MySQL驱动是成功导入而且能够使用了，然后通过查资料了解到，要解决这个错误只需要在AndroidManifest.xml文件里面加一行<uses-permission android:name="android.permission.INTERNET"/>就行了

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="cn.xuziao.faceprocess">

    <!--要加在application标签的上面-->

    <uses-permission android:name="android.permission.INTERNET"/>

    <application

        android:allowBackup="false"

        android:icon="@mipmap/real_launcher_logo"

        android:label="@string/app_name"

        android:roundIcon="@mipmap/ic_launcher_round"

        android:supportsRtl="true"

        android:theme="@style/Theme.FaceProcess"

        >

        <activity

            android:name=".LoginActivity"

            android:exported="true"

            android:theme="@android:style/Theme.NoTitleBar.Fullscreen"

            >

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

        <activity

            android:name=".MainActivity"

            android:exported="true"/>

    </application>

</manifest>

然后问题成功解决

总结

1. 安卓连接网络要使用多线程，不能直接用主线程

2. MySQL驱动版本不宜过高，我这边试的5是可以的，8不行，至于6、7暂时还不清楚

之后我又新建了一个Java工程，用的jdk8但是使用MySQL8的驱动是可以正确连接的，不知道Android为什么不行，如果有知道的希望能在评论区一起分享一下

3. 要记得在`AndroidManifest.xml`文件里面加上`<uses-permission android:name="android.permission.INTERNET"/>`这一行