Question

我正在努力创建一个非常简单的类来向Oracle XE 11g实例发送查询，实质上是使用非常简单的SQL * Plus来实现JDBC的基础知识。

我目前使用的源代码是：

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);
            }
        }

    }
}

在第二个try / catch块中，在for(;;)循环中，我得到以下输出：

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)

我检查了Oracle docs（java.lang.AbstractMethodError），它说只有在以下情况下才会抛出此错误：

＆＃34;自上次编译当前执行的方法以来，某些类的定义发生了不相同的变化。＆＃34;

我认为第27行有一些我不知道的东西，但我不确定如何解决这个问题，任何指导都会非常有帮助。

Answer 1

我认为您的问题是由于您使用JDBC驱动程序用于Java＆lt; = 6版本而使用Java 7或更高版本，因为Java 7中添加了方法Connection#getSchema()。

使用最新版本的JDBC驱动程序来避免此类问题，或者至少使用与您的Java版本兼容的JDBC驱动程序。

Answer 2

这适用于DB2（和旧版本的驱动程序）

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使用java.sql.Connection

2 个答案: