JAVA JDBC 与列表返回有关的问题

Question

长期潜伏者。我一直在 Java 中工作，试图执行我拥有的这个 JDBC SQL 语句，有时可以将类作为静态空运行获得结果。当我尝试将结果集制作成列表并返回它时，我在底部附加了错误日志。如果我没有正确发布某些内容，我会事先道歉。很可能我错过了一些东西，但似乎无法让我的眼睛注意到它。

提前致谢

附言温柔一点，这是我的第一次。

珠子

///

protected void onCreate(Bundle savedInstanceState) {
int SDK_INT = android.os.Build.VERSION.SDK_INT;
if (SDK_INT > 8)
{
StrictMode.ThreadPolicy policy = new 
StrictMode.ThreadPolicy.Builder()
.permitAll().build();
StrictMode.setThreadPolicy(policy);
//your codes here
}
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

SQLEvent EVENTS = new SQLEvent();
List<List<String>> EventString = EVENTS.main();
System.out.println("EVENT RESULTS: " + EventString);

///

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
public class SQLEvent{
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://***.***.***.***:3306/DB_NAME?useSSL=false&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC";
//  Database credentials
static final String USER = "*******";
static final String PASS = "*******";



public List <List<String>>  main() {
ResultSet rs = null;
Connection conn = null;
java.sql.PreparedStatement stmt = null;
List<List<String>> result = new ArrayList<>();
try {
//STEP 2: Register JDBC driver
Class.forName("com.mysql.cj.jdbc.Driver").newInstance();
//STEP 3: Open a connection
System.out.println("Connecting to database...");
conn = DriverManager.getConnection(DB_URL, USER, PASS);
//STEP 4: Execute a query
System.out.println("Creating statement...");
String sql = "SELECT * FROM events WHERE LOC= ?";
stmt = conn.prepareStatement(sql);
//Bind values into the parameters.
stmt.setString(1, "matts office");  // This would set age
// Let us update age of the record with ID = 102;
//int rows = stmt.executeUpdate();
//  System.out.println("Rows impacted : " + rows );
// Let us select all the records and display them.
// sql = "SELECT id, first, last, age FROM Employees";
// stmt.setInt(1, 1001);
rs = stmt.executeQuery();
int numcols = rs.getMetaData().getColumnCount();

//STEP 5: Extract data from result set
while (rs.next()) {
List<String> row = new ArrayList<>(numcols); // new list per row
int i = 1;
while (i <= numcols) {  // don't skip the last column, use <=
row.add(rs.getString(i++));
}
result.add(row); // add it to the result
//Retrieve by column name
int id = rs.getInt("id");
String LOC = rs.getString("LOC");
String EventName = rs.getString("EventName");
String EventDesc = rs.getString("EventDesc");
String Closed = rs.getString("Closed");
String TimeStart = rs.getString("TimeStart");
String TimeEnd = rs.getString("TimeEnd");

//Display values
System.out.print("ID: " + id);
System.out.print(", Location: " + LOC);
System.out.print(", Event Name: " + EventName);
System.out.println(", Event Description: " + EventDesc);
System.out.println(", Closed: " + Closed);
System.out.println(", Time Start: " + TimeStart);
System.out.println(", Time End: " + TimeEnd);
}
//STEP 6: Clean-up environment
if (!rs.next()) {
} else {
//  MainActivity MA = new MainActivity();
// MA.NotificationEvent();
}
stmt.close();
conn.close();
System.out.println("Result Set: " + result);
rs.close();


} catch (SQLException se) {
//Handle errors for JDBC
se.printStackTrace();
} catch (Exception e) {
//Handle errors for Class.forName
e.printStackTrace();
} finally {
//finally block used to close resources
try {
if (stmt != null)
stmt.close();
} catch (SQLException se2) {
}// nothing we can do
try {
if (conn != null)
conn.close();
} catch (SQLException se) {
se.printStackTrace();
}//end finally try
}//end try
System.out.println("Goodbye!");

return result;
}

}

///

07-02 18:02:43.286 11991-11991/com.internalpositioning.find3.find3app E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.internalpositioning.find3.find3app, PID: 11991
java.lang.BootstrapMethodError: Exception from call site #145 bootstrap method
at com.mysql.cj.conf.ConnectionUrl.buildConnectionStringCacheKey(ConnectionUrl.java:236)
at com.mysql.cj.conf.ConnectionUrl.getConnectionUrlInstance(ConnectionUrl.java:167)
at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:201)
at java.sql.DriverManager.getConnection(DriverManager.java:569)
at java.sql.DriverManager.getConnection(DriverManager.java:219)
at com.internalpositioning.find3.find3app.SQLEvent.main(SQLEvent.java:45)
at com.internalpositioning.find3.find3app.MainActivity.onCreate(MainActivity.java:144)
at android.app.Activity.performCreate(Activity.java:7009)
at android.app.Activity.performCreate(Activity.java:7000)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NoClassDefFoundError: Invalid descriptor: VIIIIIIIIII.
at com.mysql.cj.conf.ConnectionUrl.buildConnectionStringCacheKey(ConnectionUrl.java:236) 
at com.mysql.cj.conf.ConnectionUrl.getConnectionUrlInstance(ConnectionUrl.java:167) 
at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:201) 
at java.sql.DriverManager.getConnection(DriverManager.java:569) 
at java.sql.DriverManager.getConnection(DriverManager.java:219) 
at com.internalpositioning.find3.find3app.SQLEvent.main(SQLEvent.java:45) 
at com.internalpositioning.find3.find3app.MainActivity.onCreate(MainActivity.java:144) 
at android.app.Activity.performCreate(Activity.java:7009) 
at android.app.Activity.performCreate(Activity.java:7000) 
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214) 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 
at android.app.ActivityThread.-wrap11(Unknown Source:0) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:164) 
at android.app.ActivityThread.main(ActivityThread.java:6494) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 

Answer 1

我想你的MySQL驱动程序版本在Android上不起作用。似乎，它在Collectors.joining上失败了.这是在Java 8中添加的。

另外，在我看来，直接从Android连接到数据库似乎很奇怪。据我所知，通常移动应用程序会向有权访问数据库的后端层发出一些请求(通常是 REST(。