三月二十一日

很开心，今天终于连接到了。界面显示的是返回的Connection的值和我查询的一个数据库内容。

 主要的原因是MySQL8.0版本不兼容，反正我的是更换5.0版本就好了。（提醒大家不要不相信，我也在这里卡了好久，明明代码没有问题，但就是连接不上）

还有连接数据库是一个耗时的过程，要放在次线程进行，这个看网上好像说是新更新的Android 是这样。网上有好多代码可以看，主要是配置环境不对，真的不是不努力，被卡在第一步也是打击很大的。

简单的看一下我的代码，只是简单的实现一个查询。

MainActivity

package com.example.myapplicatio1;


import android.annotation.SuppressLint;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

import java.nio.file.FileSystemLoopException;
import java.sql.Connection;

public class MainActivity extends AppCompatActivity {
    public Connection coon = null;
    TextView address = null;
    TextView result = null;
    String re = null;
    User user =null;
    utilDao dao = new utilDao();
    @SuppressLint("MissingInflatedId")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        result = findViewById(R.id.result);

        user = new User("1","1");
        Thread thread =new Thread(new Runnable() {
            @Override
            public void run() {
                address = findViewById(R.id.add);
                coon = getConnection.getcoon();
                address.setText(String.valueOf(coon));
                re = dao.select(user);
//                re = "sdf"+
                result.setText(re);
          }
        });thread.start();
    }
}

连接数据库的封装类

package com.example.myapplicatio1;

import java.sql.*;
public class getConnection {
    private static Connection connection = null;
    private static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    private static final String DATABASE_URL = "jdbc:mysql://10.99.113.81/user";
    private static final String DATABASE_USER = "Android";
    private static final String DATABASE_PASSWORD = "246437";

    public static Connection getcoon() {
        try {
            // Load the JDBC driver
            Class.forName(JDBC_DRIVER);
            // Establish a connection
            connection = DriverManager.getConnection(DATABASE_URL, DATABASE_USER, DATABASE_PASSWORD);
            // You now have a connection to the database
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return connection;
    }
}

User类,就是数据库主要的内容，我的是有三个。

package com.example.myapplicatio1;

public class User {
    private String name;
    private String password;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public User(String name, String password) {
        super();
        this.name = name;
        this.password = password;
    }
    @Override
    public String toString() {
        return "User [name=" + name + ", password=" + password + "]";
    }



}

查询数据库内容

package com.example.myapplicatio1;

import java.sql.SQLException;
import java.sql.*;
public class utilDao {
    String  identity;
    //查询
    public String select(User user)
    {
        Connection coon = getConnection.getcoon();
        String sql = "select identity from information where name=? and password = ? ";
        try {
            PreparedStatement ps = coon.prepareStatement(sql);
            ps.setString(1, user.getName());
            ps.setString(2, user.getPassword());
            ResultSet re = ps.executeQuery();
            while(re.next())
            {
                identity = re.getString("identity");
            }
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
        return identity;
    }
}

　　这个是我的navicat一个数据库图形化工具。

 也有好久了，明天终于可以开始后面的进度了。