The error information is as follows:

E/AndroidRuntime: FATAL EXCEPTION: Thread-4
    Process: com.example.NCEPU, PID: 19597
    java.lang.NoClassDefFoundError: Failed resolution of: Ljava/sql/SQLType;
        at com.mysql.cj.jdbc.DatabaseMetaData.getInstance(DatabaseMetaData.java:746)
        at com.mysql.cj.jdbc.ConnectionImpl.getMetaData(ConnectionImpl.java:1170)
        at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:447)
        at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:246)
        at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:197)
        at java.sql.DriverManager.getConnection(DriverManager.java:580)
        at java.sql.DriverManager.getConnection(DriverManager.java:218)
        at com.example.NCEPU.Utils.MySQLUtil$1.run(MySQLUtil.java:20)
        at java.lang.Thread.run(Thread.java:929)
     Caused by: java.lang.ClassNotFoundException: Didn't find class "java.sql.SQLType" on path: DexPathList[[zip file "/data/app/com.example.NCEPU-ONfkLzQBKVHb0mVXKR3p5g==/base.apk"],nativeLibraryDirectories=[/data/app/com.example.NCEPU-ONfkLzQBKVHb0mVXKR3p5g==/lib/arm64, /data/app/com.example.NCEPU-ONfkLzQBKVHb0mVXKR3p5g==/base.apk!/lib/arm64-v8a, /system/lib64, /system/product/lib64, /hw_product/lib64, /system/product/lib64]]
        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:196)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
        at com.mysql.cj.jdbc.DatabaseMetaData.getInstance(DatabaseMetaData.java:746) 
        at com.mysql.cj.jdbc.ConnectionImpl.getMetaData(ConnectionImpl.java:1170) 
        at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:447) 
        at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:246) 
        at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:197) 
        at java.sql.DriverManager.getConnection(DriverManager.java:580) 
        at java.sql.DriverManager.getConnection(DriverManager.java:218) 
        at com.example.NCEPU.Utils.MySQLUtil$1.run(MySQLUtil.java:20) 
        at java.lang.Thread.run(Thread.java:929) 
W/libEGL: EGLNativeWindowType 0x6f3882b950 disconnect failed
I/Process: Sending signal. PID: 19597 SIG: 9

Problem analysis: the jar package version of MySQL is too high. I used the latest version: mysql-connector-java-8.0.21.jar, loading driver:

Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://yourip:port/sheetname?useSSL=false&allowPublicKeyRetrieval=true&serverTimezone=UTC";
connection = DriverManager.getConnection(url, user, password);

Problem solved: jar version lower, here I used the official website to download mysql-connector-java-5.1.49.jar, note that after changing to a lower version to load the driver to become.

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

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