使用 java.sql.Connection 在运行时抛出 AbstractMethodError

Question

I'm trying to work through creating a very simple class to send queries to an instance of Oracle XE 11g, essentially making a very simple SQL*Plus to get the basics of JDBC down.

The source code I'm currently working with is:

public class Example {
    static String username, password;
    static String dbDriver = "oracle.jdbc.driver.OracleDriver";
    static String dbConnection = "jdbc:oracle:thin:@//localhost:1521/xe";

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String line;
        Connection c = null;
        Statement stmt = null;
        int loginAttempts = 0;

        // Log in loop
        do {
            try {
                Class.forName(dbDriver);
                System.out.print("Enter username: ");
                line = input.nextLine();
                if (line.contains("/")) {
                    String[] login = line.split("/");
                    if (login.length != 2) {
                        System.out
                                .println("Unrecognized information, exiting...");
                        System.exit(0);
                    }

                    username = login[0].trim();
                    password = login[1].trim();
                } else {
                    username = line;
                    System.out.print("Enter password: ");
                    password = input.nextLine();
                }

                c = DriverManager.getConnection(dbConnection, username,
                        password);
                stmt = c.createStatement();
                loginAttempts = -1;
            } catch (ClassNotFoundException e) {
                System.err.println("Unable to connect to database, exiting...");
                System.exit(-1);
            } catch (SQLException e) {
                System.out.println("Username and/or password is incorrect");
                if (++loginAttempts == 1) {
                    System.out.println("Too many failed login attempts, exiting...");
                    System.exit(0);
                }
            }
        } while (loginAttempts != -1);

        // Input loop
        for (;;) {
            try {
                // Write out the prompt text and wait for input
                if(c == null) {
                    throw new IllegalStateException("Connection should not be null");
                }
                System.out.print(c.getSchema() + ":> ");
                String tmp = input.nextLine();

                // Check if the user entered "exit"
                if (tmp.toLowerCase().equals("exit")) {
                    System.out.println("Exiting...");
                    input.close();
                    System.exit(0);
                }

                String query;
                // TODO: For some reason, no semi-colon is allowed
                if (tmp.charAt(tmp.length() - 1) == ';')
                    query = tmp.split(";")[0];
                else
                    query = tmp;
                // System.out.println(query);
                ResultSet rset = stmt.executeQuery(query);
                ResultSetMetaData rmd = rset.getMetaData();
                int colCount = rmd.getColumnCount();

                // Column indices start with 1, print column names
                for (int i = 1; i <= colCount; i++) {
                    System.out.printf("%-20.20s   ", rmd.getColumnName(i));
                }
                System.out.println();

                while (rset.next()) {
                    for (int i = 0; i < colCount; i++) {
                        System.out.printf("%-20.20s | ", rset.getString(i + 1));
                    }
                    System.out.println();
                }
                System.out.println();
            } catch (SQLSyntaxErrorException e) {
                System.out.println("Encountered a syntax error:\n"
                        + e.getMessage());
            } catch (SQLException e) {
                System.err.println("An unexpected error occurred");
                e.printStackTrace();
                input.close();
                System.exit(-1);
            }
        }

    }
}

In the second try/catch block, in the for(;;) loop, I get the following output:

Enter username: hr/hr
Exception in thread "main" java.lang.AbstractMethodError: oracle.jdbc.driver.T4CConnection.getSchema()Ljava/lang/String;
at jdbctest.Example.main(Example.java:69)

I checked out the Oracle docs (java.lang.AbstractMethodError), and it says that this error can only be thrown if:

"the definition of some class has incompatibly changed since the currently executing method was last compiled."

I'm thinking that there's something I'm missing with line 27, but I'm not sure how to approach this problem and any guidance would be extremely helpful.

Answer 1

I believe that your problem is due to the fact that you use a JDBC driver for a version of Java <= 6 and you use Java 7 or higher because the method Connection#getSchema() has been added in Java 7.

Use the latest version of your JDBC driver to avoid such issue or at least a JDBC driver compatible with your version of Java.

Answer 2

这适用于 DB2（和旧版本的驱动程序）

Connection.getMetaData().getConnection().getSchema();