Question

我有以下代码：

Connection conn = null;
    Statement stmt = null;

    // MySQL connection details.
    String username = ("username");
    String password = ("password");
    String url = ("jdbc:derby://localhost:1527/OnlineLibrary");

    try {

        // Connect to database. 
        Class.forName("org.apache.derby.jdbc.ClientDriver").newInstance();               
        conn = DriverManager.getConnection (url, username, password);            
        stmt = conn.createStatement();

        // Get data.
        String query = ("SELECT PersonNo, Forename, Surname FROM Person;");                       
        ResultSet rs = stmt.executeQuery(query);               
        while (rs.next()) {                
            System.out.println("Person: no: " + rs.getInt("PersonNo") + " name: " + rs.getString("Forename") + " " + rs.getString("Surname"));
        }                 

        // Disconnect from database.
        stmt.close();
        conn.close();
    }
    catch(Exception ex) {
        Java_Utils.printStackTrace("Error connecting to database", ex, true);    
    }

这给了我：

Error connecting to database
org.apache.derby.client.am.SQLExceptionFactory40.getSQLException(Unknown Source)
org.apache.derby.client.am.SqlException.getSQLException(Unknown Source)
org.apache.derby.client.am.Statement.executeQuery(Unknown Source)
misc.Simple_JDBC_Test.main(Simple_JDBC_Test.java:32)

对我来说，一切似乎都没问题。我可以使用连接池连接到数据库，但我不明白上述错误。

Answer 1

@Mr Morgan，
使用PreparedStatement而不是Statement，意味着替换

ResultSet rs = stmt.executeQuery（query）;
与

ProblemStatement pStmt = dbConnection.prepareStatement（query）;

ResultSet r = pStmt.executeQuery（）;

这样做后请显示你的输出！

Answer 2

在语句末尾删除semicolomn ; 符号：

String query = ("SELECT PersonNo, Forename, Surname FROM Person");

然后在 OnLineLibrary 数据库中直接执行相关查询以检查其输出以及语法是否正确：

SELECT PersonNo, Forename, Surname FROM Person

尝试使用JDBC连接到Java Derby数据库

2 个答案: