Android应用强制停止运行

Question

问题描述

我按了修改按钮之后，本来会执行数据库命令，为什么按了之后会停止运行？

问题出现的环境背景及自己尝试过哪些方法

我本想练习一下Android studio连接SQL server并执行sql语句

相关代码

// 请把代码文本粘贴到下方（请勿用图片代替代码）
1.MainActivity.java:
package com.example.myapplication;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import com.google.android.material.floatingactionbutton.FloatingActionButton;

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    final TextView text=(TextView)findViewById(R.id.text);
    Button button=(Button)findViewById(R.id.button);
    FloatingActionButton fab = findViewById(R.id.fab);
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            text.setText(DBUtil.QuerySQL());
        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // 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.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

}
2.DBUtil.java:
package com.example.myapplication;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class DBUtil {

private static Connection getSQLConnection(String ip, String user, String pwd, String db)
{
    Connection con = null;
    try
    {
        Class.forName("net.sourceforge.jtds.jdbc.Driver");
        con = DriverManager.getConnection("jdbc:jtds:sqlserver://" + ip + ":1433/" + db + ";charset=utf8", user, pwd);
    } catch (ClassNotFoundException e)
    {
        e.printStackTrace();
    } catch (SQLException e)
    {
        e.printStackTrace();
    }
    return con;
}

public static String QuerySQL()
{
    String a="";
    try {
        Connection conn = getSQLConnection("127.0.0.1", "sa", "593748", "hotel");
        String sql = "select * from 用户 where 用户姓名='zhazhazha'";
        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery(sql);
        while (rs.next()) {
            a = rs.getString("联系方式");
        }
    }
    catch (SQLException e)
    {
        e.printStackTrace();
        a="";
    }
    return a;
}

public static void main(String[] args)
{
    System.out.println(QuerySQL());
}

}
3.AndroidManifest.xml:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:dist="http://schemas.android.com/apk/distribution"
package="com.example.myapplication">
<dist:module dist:instant="true" />

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name"
        android:theme="@style/AppTheme.NoActionBar">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
    </activity>
</application>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

</manifest>
4.activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<com.google.android.material.appbar.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

</com.google.android.material.appbar.AppBarLayout>

<include layout="@layout/content_main" />

<com.google.android.material.floatingactionbutton.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    app:srcCompat="@android:drawable/ic_dialog_email" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>
5.content_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context=".MainActivity"
tools:layout_editor_absoluteY="56dp"
tools:showIn="@layout/activity_main">

<TextView
    android:id="@+id/text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<Button
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="0dp"
    android:text="修改"
    tools:ignore="MissingConstraints"
    tools:layout_editor_absoluteX="161dp"
    tools:layout_editor_absoluteY="418dp" />

</androidx.constraintlayout.widget.ConstraintLayout>

你期待的结果是什么？实际看到的错误信息又是什么？

应用界面：

执行后（按下修改按钮）界面：