ClassNotFoundException MySqlConnector 的 IntelliJ
ClassNotFoundException MySqlConnector IntelliJ
我正在使用 JavaFX 编写模板方法设计模式示例程序，但无法连接到我的 MySQL 数据库。我正在使用 IntelliJ 并将 MySQL-Connector.jar 添加到库中，但是我得到 ClassNotFoundException.
Error
java.lang.ClassNotFoundException: com.mysql.jdbc.driver
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:375)
at sample.DatabaseOperation.openConnection(DatabaseOperation.java:24)
at sample.DatabaseOperation.template(DatabaseOperation.java:14)
at sample.Controller.initialize(Controller.java:44)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3331)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3287)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3255)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3227)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3203)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3196)
at sample.Main.start(Main.java:13)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:847)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:484)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:457)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:456)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:184)
at java.base/java.lang.Thread.run(Thread.java:833)
Exception in Application start method
java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:465)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:364)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1071)
Caused by: java.lang.RuntimeException: Exception in Application start method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:901)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication(LauncherImpl.java:196)
at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: javafx.fxml.LoadException:
/C:/Users/grego/Downloads/code-with-quarkus/TemplateMethodExample/out/production/TemplateMethodExample/sample/sample.fxml
at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3331)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3287)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3255)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3227)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3203)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3196)
at sample.Main.start(Main.java:13)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:847)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:484)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:457)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:456)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:184)
... 1 more
Caused by: java.lang.NullPointerException: Cannot invoke "java.sql.Connection.createStatement()" because "this.connection" is null
at sample.InitialLoad.select(InitialLoad.java:10)
at sample.DatabaseOperation.template(DatabaseOperation.java:17)
at sample.Controller.initialize(Controller.java:44)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
... 17 more
Exception running application sample.Main
Process finished with exit code 1
模板方法
package sample;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
public abstract class DatabaseOperation {
public Connection connection;
public ResultSet resultSet;
public final ResultSet template() throws SQLException {
openConnection();
insert();
update();
select();
closeConnection();
return resultSet;
}
public final void openConnection() {
try {
Class.forName("com.mysql.jdbc.driver");
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/employees", "user", "password");
} catch (ClassNotFoundException | SQLException e) {
e.printStackTrace();
}
}
public final void closeConnection(){
try {
connection.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
System.out.println("Connection closed");
}
public abstract void select() throws SQLException;
public abstract void insert();
public abstract void update();
}
Class 扩展模板
package sample;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class InitialLoad extends DatabaseOperation {
@Override
public void select() throws SQLException {
Statement statement = connection.createStatement();
resultSet = statement.executeQuery("select * from employees");
}
@Override
public void insert() {
}
@Override
public void update() {
}
}
控制器
package sample;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.PropertyValueFactory;
import javax.xml.crypto.Data;
import java.net.URL;
import java.sql.SQLException;
import java.util.ResourceBundle;
public class Controller implements Initializable {
public TableColumn col_emp_no;
public TableColumn col_birth_date;
public TableColumn col_first_name;
public TableColumn col_last_name;
public TableColumn col_gender;
public TableColumn col_hire_date;
@FXML
TableView tableView;
@Override
public void initialize(URL url, ResourceBundle resourceBundle) {
col_emp_no.setCellValueFactory(new PropertyValueFactory<>("emp_no"));
col_birth_date.setCellValueFactory(new PropertyValueFactory<>("birth_date"));
col_first_name.setCellValueFactory(new PropertyValueFactory<>("first_name"));
col_last_name.setCellValueFactory(new PropertyValueFactory<>("last_name"));
col_gender.setCellValueFactory(new PropertyValueFactory<>("gender"));
col_hire_date.setCellValueFactory(new PropertyValueFactory<>("hire_date"));
DatabaseOperation initialLoad = new InitialLoad();
try {
initialLoad.template();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
主要
package sample;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class Main extends Application {
@Override
public void start(Stage primaryStage) throws Exception{
Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
primaryStage.setTitle("Hello World");
primaryStage.setScene(new Scene(root, 300, 275));
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
提前致谢！
更新：
我在使用 Maven 时仍然遇到同样的错误
[INFO]
[INFO] --- javafx-maven-plugin:0.0.6:run (default-cli) @ TemplateMethodMaven ---
[INFO] Toolchain in javafx-maven-plugin null
java.lang.ClassNotFoundException: com.mysql.jdbc.driver
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:636)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:182)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:519)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:375)
at org.example.DatabaseOperation.openConnection(DatabaseOperation.java:24)
at org.example.DatabaseOperation.template(DatabaseOperation.java:14)
at org.example.PrimaryController.initialize(PrimaryController.java:44)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:2516)
at org.example.App.loadFXML(App.java:31)
at org.example.App.start(App.java:20)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:847)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:484)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:457)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:456)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:184)
at java.base/java.lang.Thread.run(Thread.java:831)
Exception in Application start method
java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:465)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:364)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1071)
Caused by: java.lang.RuntimeException: Exception in Application start method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:901)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication(LauncherImpl.java:196)
at java.base/java.lang.Thread.run(Thread.java:831)
Caused by: javafx.fxml.LoadException:
/C:/Users/grego/Downloads/code-with-quarkus/TemplateMethodMaven/target/classes/org/example/primary.fxml
at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:2516)
at org.example.App.loadFXML(App.java:31)
at org.example.App.start(App.java:20)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:847)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:484)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:457)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:456)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:184)
... 1 more
Caused by: java.lang.NullPointerException: Cannot invoke "java.sql.Connection.createStatement()" because "this.connection" is null
at org.example.InitialLoad.select(InitialLoad.java:10)
at org.example.DatabaseOperation.template(DatabaseOperation.java:17)
at org.example.PrimaryController.initialize(PrimaryController.java:44)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
... 13 more
Exception running application org.example.App
[ERROR] Command execution failed.
org.apache.commons.exec.ExecuteException: Process exited with an error: 1 (Exit value: 1)
at org.apache.commons.exec.DefaultExecutor.executeInternal (DefaultExecutor.java:404)
at org.apache.commons.exec.DefaultExecutor.execute (DefaultExecutor.java:166)
at org.openjfx.JavaFXBaseMojo.executeCommandLine (JavaFXBaseMojo.java:567)
at org.openjfx.JavaFXBaseMojo.executeCommandLine (JavaFXBaseMojo.java:434)
at org.openjfx.JavaFXRunMojo.execute (JavaFXRunMojo.java:105)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:77)
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke (Method.java:568)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
at org.codehaus.classworlds.Launcher.main (Launcher.java:47)
org.apache.commons.exec.ExecuteException: Process exited with an error: 1 (Exit value: 1)
at org.apache.commons.exec.DefaultExecutor.executeInternal(DefaultExecutor.java:404)
at org.apache.commons.exec.DefaultExecutor.execute(DefaultExecutor.java:166)
at org.openjfx.JavaFXBaseMojo.executeCommandLine(JavaFXBaseMojo.java:567)
at org.openjfx.JavaFXBaseMojo.executeCommandLine(JavaFXBaseMojo.java:434)
at org.openjfx.JavaFXRunMojo.execute(JavaFXRunMojo.java:105)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:137)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:210)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:56)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:305)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:192)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:105)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:957)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:289)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:193)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:282)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:225)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:406)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:347)
at org.codehaus.classworlds.Launcher.main(Launcher.java:47)
参见this guide for Idea JavaFX project setup，具体参考添加额外模块部分。
您需要添加的maven module for the mysql JDBC connector：
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.28</version>
</dependency>
如果您不提供 module-info.java，您的应用程序代码将在 class 路径上，并且 mysql 连接器也将在 class 路径上, 因此无需额外更改即可访问。
如果您提供 module-info.java，您将需要在 module-info 中要求适当的模块。java:
requires java.sql 用于标准 jdbc 和 sql 访问代码。requires mysql.connector.java 用于 mysql jdbc 驱动程序。
示例module-info.java（替换模块名称并根据需要修改需求条款）：
module com.example.sql {
requires javafx.controls;
requires javafx.fxml;
requires mysql.connector.java;
requires java.sql;
opens com.example.sql to javafx.fxml;
exports com.example.sql;
}
当您尝试打开数据库连接时，您会看到此代码，该代码既错误又不必要，原因有多种：
Class.forName("com.mysql.jdbc.driver");
一旦通过添加正确的库和模块命令正确配置了访问，执行此行会导致以下警告：
Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.
所以两者都是：
驱动名称错误，应该是com.mysql.cj.jdbc.Driver
和
您不需要显式加载驱动程序
jdbc系统会根据需要通过service provider interface自动加载它。 SPI 很复杂，您不必担心它实际如何工作，只需假设它确实如此。
更多信息在对以下问题的回答中：
在 Oracle jdbc tutorial 之后，您将获得如下连接代码：
public Connection getConnection() throws SQLException {
Properties connectionProps = new Properties();
connectionProps.put("user", "apple");
connectionProps.put("password", "cider");
Connection conn = DriverManager.getConnection(
"jdbc:mysql://localhost:1433/",
connectionProps
);
System.out.println("Connected to database");
return conn;
}
从 start 方法调用此方法似乎试图为我启动连接（它实际上没有连接，因为我没有设置本地 mysql 服务器）。
我正在使用 JavaFX 编写模板方法设计模式示例程序，但无法连接到我的 MySQL 数据库。我正在使用 IntelliJ 并将 MySQL-Connector.jar 添加到库中，但是我得到 ClassNotFoundException.
Error
java.lang.ClassNotFoundException: com.mysql.jdbc.driver
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:375)
at sample.DatabaseOperation.openConnection(DatabaseOperation.java:24)
at sample.DatabaseOperation.template(DatabaseOperation.java:14)
at sample.Controller.initialize(Controller.java:44)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3331)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3287)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3255)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3227)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3203)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3196)
at sample.Main.start(Main.java:13)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:847)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:484)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:457)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:456)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:184)
at java.base/java.lang.Thread.run(Thread.java:833)
Exception in Application start method
java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:465)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:364)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1071)
Caused by: java.lang.RuntimeException: Exception in Application start method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:901)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication(LauncherImpl.java:196)
at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: javafx.fxml.LoadException:
/C:/Users/grego/Downloads/code-with-quarkus/TemplateMethodExample/out/production/TemplateMethodExample/sample/sample.fxml
at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3331)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3287)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3255)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3227)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3203)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3196)
at sample.Main.start(Main.java:13)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:847)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:484)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:457)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:456)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:184)
... 1 more
Caused by: java.lang.NullPointerException: Cannot invoke "java.sql.Connection.createStatement()" because "this.connection" is null
at sample.InitialLoad.select(InitialLoad.java:10)
at sample.DatabaseOperation.template(DatabaseOperation.java:17)
at sample.Controller.initialize(Controller.java:44)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
... 17 more
Exception running application sample.Main
Process finished with exit code 1
模板方法
package sample;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
public abstract class DatabaseOperation {
public Connection connection;
public ResultSet resultSet;
public final ResultSet template() throws SQLException {
openConnection();
insert();
update();
select();
closeConnection();
return resultSet;
}
public final void openConnection() {
try {
Class.forName("com.mysql.jdbc.driver");
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/employees", "user", "password");
} catch (ClassNotFoundException | SQLException e) {
e.printStackTrace();
}
}
public final void closeConnection(){
try {
connection.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
System.out.println("Connection closed");
}
public abstract void select() throws SQLException;
public abstract void insert();
public abstract void update();
}
Class 扩展模板
package sample;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class InitialLoad extends DatabaseOperation {
@Override
public void select() throws SQLException {
Statement statement = connection.createStatement();
resultSet = statement.executeQuery("select * from employees");
}
@Override
public void insert() {
}
@Override
public void update() {
}
}
控制器
package sample;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.PropertyValueFactory;
import javax.xml.crypto.Data;
import java.net.URL;
import java.sql.SQLException;
import java.util.ResourceBundle;
public class Controller implements Initializable {
public TableColumn col_emp_no;
public TableColumn col_birth_date;
public TableColumn col_first_name;
public TableColumn col_last_name;
public TableColumn col_gender;
public TableColumn col_hire_date;
@FXML
TableView tableView;
@Override
public void initialize(URL url, ResourceBundle resourceBundle) {
col_emp_no.setCellValueFactory(new PropertyValueFactory<>("emp_no"));
col_birth_date.setCellValueFactory(new PropertyValueFactory<>("birth_date"));
col_first_name.setCellValueFactory(new PropertyValueFactory<>("first_name"));
col_last_name.setCellValueFactory(new PropertyValueFactory<>("last_name"));
col_gender.setCellValueFactory(new PropertyValueFactory<>("gender"));
col_hire_date.setCellValueFactory(new PropertyValueFactory<>("hire_date"));
DatabaseOperation initialLoad = new InitialLoad();
try {
initialLoad.template();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
主要
package sample;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class Main extends Application {
@Override
public void start(Stage primaryStage) throws Exception{
Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
primaryStage.setTitle("Hello World");
primaryStage.setScene(new Scene(root, 300, 275));
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
提前致谢！
更新：
我在使用 Maven 时仍然遇到同样的错误
[INFO]
[INFO] --- javafx-maven-plugin:0.0.6:run (default-cli) @ TemplateMethodMaven ---
[INFO] Toolchain in javafx-maven-plugin null
java.lang.ClassNotFoundException: com.mysql.jdbc.driver
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:636)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:182)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:519)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:375)
at org.example.DatabaseOperation.openConnection(DatabaseOperation.java:24)
at org.example.DatabaseOperation.template(DatabaseOperation.java:14)
at org.example.PrimaryController.initialize(PrimaryController.java:44)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:2516)
at org.example.App.loadFXML(App.java:31)
at org.example.App.start(App.java:20)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:847)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:484)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:457)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:456)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:184)
at java.base/java.lang.Thread.run(Thread.java:831)
Exception in Application start method
java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:465)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:364)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1071)
Caused by: java.lang.RuntimeException: Exception in Application start method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:901)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication(LauncherImpl.java:196)
at java.base/java.lang.Thread.run(Thread.java:831)
Caused by: javafx.fxml.LoadException:
/C:/Users/grego/Downloads/code-with-quarkus/TemplateMethodMaven/target/classes/org/example/primary.fxml
at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:2516)
at org.example.App.loadFXML(App.java:31)
at org.example.App.start(App.java:20)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:847)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:484)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:457)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:456)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:184)
... 1 more
Caused by: java.lang.NullPointerException: Cannot invoke "java.sql.Connection.createStatement()" because "this.connection" is null
at org.example.InitialLoad.select(InitialLoad.java:10)
at org.example.DatabaseOperation.template(DatabaseOperation.java:17)
at org.example.PrimaryController.initialize(PrimaryController.java:44)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
... 13 more
Exception running application org.example.App
[ERROR] Command execution failed.
org.apache.commons.exec.ExecuteException: Process exited with an error: 1 (Exit value: 1)
at org.apache.commons.exec.DefaultExecutor.executeInternal (DefaultExecutor.java:404)
at org.apache.commons.exec.DefaultExecutor.execute (DefaultExecutor.java:166)
at org.openjfx.JavaFXBaseMojo.executeCommandLine (JavaFXBaseMojo.java:567)
at org.openjfx.JavaFXBaseMojo.executeCommandLine (JavaFXBaseMojo.java:434)
at org.openjfx.JavaFXRunMojo.execute (JavaFXRunMojo.java:105)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:77)
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke (Method.java:568)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
at org.codehaus.classworlds.Launcher.main (Launcher.java:47)
org.apache.commons.exec.ExecuteException: Process exited with an error: 1 (Exit value: 1)
at org.apache.commons.exec.DefaultExecutor.executeInternal(DefaultExecutor.java:404)
at org.apache.commons.exec.DefaultExecutor.execute(DefaultExecutor.java:166)
at org.openjfx.JavaFXBaseMojo.executeCommandLine(JavaFXBaseMojo.java:567)
at org.openjfx.JavaFXBaseMojo.executeCommandLine(JavaFXBaseMojo.java:434)
at org.openjfx.JavaFXRunMojo.execute(JavaFXRunMojo.java:105)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:137)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:210)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:56)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:305)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:192)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:105)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:957)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:289)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:193)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:282)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:225)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:406)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:347)
at org.codehaus.classworlds.Launcher.main(Launcher.java:47)
参见this guide for Idea JavaFX project setup，具体参考添加额外模块部分。
您需要添加的maven module for the mysql JDBC connector：
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.28</version>
</dependency>
如果您不提供 module-info.java，您的应用程序代码将在 class 路径上，并且 mysql 连接器也将在 class 路径上, 因此无需额外更改即可访问。
如果您提供 module-info.java，您将需要在 module-info 中要求适当的模块。java:
requires java.sql用于标准 jdbc 和 sql 访问代码。requires mysql.connector.java用于 mysql jdbc 驱动程序。
示例module-info.java（替换模块名称并根据需要修改需求条款）：
module com.example.sql {
requires javafx.controls;
requires javafx.fxml;
requires mysql.connector.java;
requires java.sql;
opens com.example.sql to javafx.fxml;
exports com.example.sql;
}
当您尝试打开数据库连接时，您会看到此代码，该代码既错误又不必要，原因有多种：
Class.forName("com.mysql.jdbc.driver");
一旦通过添加正确的库和模块命令正确配置了访问，执行此行会导致以下警告：
Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.
所以两者都是：
驱动名称错误，应该是
com.mysql.cj.jdbc.Driver和
您不需要显式加载驱动程序
jdbc系统会根据需要通过service provider interface自动加载它。 SPI 很复杂，您不必担心它实际如何工作，只需假设它确实如此。
更多信息在对以下问题的回答中：
在 Oracle jdbc tutorial 之后，您将获得如下连接代码：
public Connection getConnection() throws SQLException {
Properties connectionProps = new Properties();
connectionProps.put("user", "apple");
connectionProps.put("password", "cider");
Connection conn = DriverManager.getConnection(
"jdbc:mysql://localhost:1433/",
connectionProps
);
System.out.println("Connected to database");
return conn;
}
从 start 方法调用此方法似乎试图为我启动连接（它实际上没有连接，因为我没有设置本地 mysql 服务器）。