java - mysql和java jdbc从另一个类调用[运行时应用程序]

Question

问题是由于 **app.java ** 被调用以响应插件启动，即在运行时环境中。我也尝试在运行时-EclipseApplication 中添加“mysql-connector-java-5.1.18-bin”，但它仍然无法工作。

我的 mysql/java 连接在独立时工作正常，但我无法开发连接并在从另一个类调用连接时出现异常。

我创建了一个类DataAccessHelper.java

        package dataBase;


        import java.sql.Connection;
        import java.sql.DriverManager;
        import java.sql.PreparedStatement;
        import java.sql.ResultSet;
        import java.sql.SQLException;
        import java.sql.Statement;
        import java.util.Date;

        public class DataAccessHelper {
            private Connection connect = null;
            private Statement statement = null;
            private PreparedStatement preparedStatement = null;
            private ResultSet resultSet = null;

            public void readDataBase() throws Exception {
                try {
                    // This will load the MySQL driver, each DB has its own driver
                    Class.forName("com.mysql.jdbc.Driver");
                    // Setup the connection with the DB
                    connect = DriverManager
                            .getConnection("jdbc:mysql://localhost/feedback?"
                                    + "user=sqluser&password=sqluserpw");

                    // Statements allow to issue SQL queries to the database
                    statement = connect.createStatement();
                    // Result set get the result of the SQL query
                    resultSet = statement
                            .executeQuery("select * from FEEDBACK.COMMENTS");
                    writeResultSet(resultSet);

                    // PreparedStatements can use variables and are more efficient
                    preparedStatement = connect
                            .prepareStatement("insert into  FEEDBACK.COMMENTS values (default, ?, ?, ?, ? , ?, ?)");
                    // "myuser, webpage, datum, summery, COMMENTS from FEEDBACK.COMMENTS");
                    // Parameters start with 1
                    preparedStatement.setString(1, "Test");
                    preparedStatement.setString(2, "TestEmail");
                    preparedStatement.setString(3, "TestWebpage");
                    preparedStatement.setDate(4, new java.sql.Date(2009, 12, 11));
                    preparedStatement.setString(5, "TestSummary");
                    preparedStatement.setString(6, "TestComment");
                    preparedStatement.executeUpdate();

                    preparedStatement = connect
                            .prepareStatement("SELECT myuser, webpage, datum, summery, COMMENTS from FEEDBACK.COMMENTS");
                    resultSet = preparedStatement.executeQuery();
                    writeResultSet(resultSet);

                    // Remove again the insert comment
                    preparedStatement = connect
                    .prepareStatement("delete from FEEDBACK.COMMENTS where myuser= ? ; ");
                    preparedStatement.setString(1, "Test");
                    preparedStatement.executeUpdate();

                    resultSet = statement
                    .executeQuery("select * from FEEDBACK.COMMENTS");
                    writeMetaData(resultSet);

                } catch (Exception e) {
                    throw e;
                } finally {
                    close();
                }

            }

            private void writeMetaData(ResultSet resultSet) throws SQLException {
                //  Now get some metadata from the database
                // Result set get the result of the SQL query

                System.out.println("The columns in the table are: ");

                System.out.println("Table: " + resultSet.getMetaData().getTableName(1));
                for  (int i = 1; i<= resultSet.getMetaData().getColumnCount(); i++){
                    System.out.println("Column " +i  + " "+ resultSet.getMetaData().getColumnName(i));
                }
            }

            private void writeResultSet(ResultSet resultSet) throws SQLException {
                // ResultSet is initially before the first data set
                while (resultSet.next()) {
                    // It is possible to get the columns via name
                    // also possible to get the columns via the column number
                    // which starts at 1
                    // e.g. resultSet.getSTring(2);
                    String user = resultSet.getString("myuser");
                    String website = resultSet.getString("webpage");
                    String summery = resultSet.getString("summery");
                    Date date = resultSet.getDate("datum");
                    String comment = resultSet.getString("comments");
                    System.out.println("User: " + user);
                    System.out.println("Website: " + website);
                    System.out.println("Summery: " + summery);
                    System.out.println("Date: " + date);
                    System.out.println("Comment: " + comment);
                }
            }

            // You need to close the resultSet
            private void close() {
                try {
                    if (resultSet != null) {
                        resultSet.close();
                    }

                    if (statement != null) {
                        statement.close();
                    }

                    if (connect != null) {
                        connect.close();
                    }
                } catch (Exception e) {

                }
            }

        }

当我直接从ma​​in.java运行此类时

    package dataBase;

    public class main {
        public static void main(String[] args) throws Exception {
            DataAccessHelper dao = new DataAccessHelper();
            dao.readDataBase();
        }
    }

它运行完美。但是，当我尝试调用其他类时 App.java

    package newmodulewizrd.ui;
    import java.awt.Dimension;
    import java.awt.FlowLayout;
    import java.sql.SQLException;

    import javax.swing.JFrame;

    import org.eclipse.jdt.core.JavaModelException;

    import dataBase.DataAccessHelper;

    public class App extends JFrame {

        ScreenContainer screen;

        public App(boolean flag)
        {

        }
        public App() throws JavaModelException, ClassNotFoundException, SQLException{
            FlowLayout fl=new FlowLayout();
            this.setLayout(fl);

            screen = new ScreenContainer();
            DataAccessHelper con= new DataAccessHelper();
            try {
                con.readDataBase();
            } catch (Exception e) {
                e.printStackTrace();
            }

            newModuleWizard.bl.Module module = new newModuleWizard.bl.Module();
            screen.addScreen(new Module(module,con),"module");// Screen1
            screen.addScreen(new Description(module,con),"description");
            screen.addScreen(new PPT(module,con), "ppt");
            screen.addScreen(new Role(module,con), "role");
            screen.addScreen(new MI(module,con), "MI");

            this.add(screen);
            this.add(new Controls(screen));

            this.setSize(new Dimension(800,600));
        }

        public static void main(String[] args) throws JavaModelException, ClassNotFoundException, SQLException {
            new App().setVisible(true);

        }


    }

它给出了一个异常

 java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

显然我的问题与

相同

Java / MySQL - How to access connection from another class?

但是，我无法从中受益，因为提供的解决方案是根据提供的代码进行的，而该代码在某种程度上无法访问[很可能链接已失效]

请帮助任何人

Answer 1

我解决了我的问题。我将其发布在这里，以便遇到相同问题的任何人也可以从中受益。

您需要在 list 中添加类路径引用。请按照以下简单步骤操作:

1. 将文件夹“lib”添加到您的应用程序
2. 将“mysql-connector-java-5.1.18-bin”放入lib
3. 现在打开“MANIFEST.MF”并转到“RUNTIME”选项卡
4. 在右下角，你会看到“classpath”；点击“添加”
5. 现在添加文件夹 lib [在步骤 1 中创建] 以及 jar 文件

这样，每当运行时 EclipseApplication/OSGi 应用程序启动时，该 jar 文件也会随之导出。因此连接也将在那里可用。