java - Android Studio MainActivity 类无法连接到本地 Mysql Workbench

Question

package com.example.test

import android.os.Bundlemportandroid.view.Menu
import android.view.MenuItem
import androidx.appcompat.app.AppCompatActivity
import com.google.android.material.snackbar.Snackbar
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.android.synthetic.main.content_main.*
import java.sql.DriverManager
import com.mysql.jdbc.Driver
import java.sql.PreparedStatement
import java.sql.Connection


class MainActivity: AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle ? ) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        btnDB.setOnClickListener {
            DBConn.DBString()
        }
        setSupportActionBar(toolbar)
        fab.setOnClickListener {
            view - >
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                .setAction("Action", null)
                .show()
        }
    }
    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        // Inflate the menu; this adds items to the action bar if it is present.
        menuInflater.inflate(R.menu.menu_main, menu)
        return true
    }
    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        return when(item.itemId) {
            R.id.action_settings - > true
            else - > super.onOptionsItemSelected(item)
        }
    }
    fun DBCon() {
        try {
            val url = "jdbc:mysql://localhost:3306/Boxing"
            var conn: Connection = DriverManager.getConnection(url, "root", "Guru9")
            //conn.close();
            if (conn != null) {
                println("Connected successfully to Database")
            }
        } catch (e: Exception) {
            println(" Not connected to Database")
        }
    }
}

Answer 1

您是在模拟器中还是在真实设备中运行此应用程序？

检查这一行:

val url = "jdbc:mysql://localhost:3306/Boxing"

我猜你的 MySQL 服务器运行在你正在开发的同一台机器上，当应用程序在模拟器中运行时，你将拥有一个像 10.0.X.X 这样的 IP，所以你看不到这个本地主机，也看不到它何时在真实设备 IP 中运行也许类似于 192.168.X.X，尝试将 localhost 替换为 IP(不是 127.0.0.1)，尝试使用开发计算机的 IP