java - 创建一个类以从 derby 数据库获取值

Question

我创建了一个类来连接到 derby 数据库。在程序中，我创建了表并插入了一些水果名称作为值。我只是想知道如何创建另一个类来获取新数组中的水果名称值。

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class FruitDatabase {

    public static void main(String[] args) throws Exception {
        Connection conn = getConnection();
        Statement stmt = conn.createStatement();

        stmt.executeUpdate("drop table fruit");
        stmt.executeUpdate("create table fruit (name CHAR(15))"); 
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Apple')"); 
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Orange')");
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Banana')");
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Pineapple')");
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Mango')");
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Kiwi')");
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Grape')");
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Strawberry')");
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Pear')");
        stmt.executeUpdate("INSERT INTO fruit(name)VALUES('Peach')");
        ResultSet rs = stmt.executeQuery("SELECT * FROM fruit"); 
        outputResultSet(rs);

        rs.close();
        stmt.close();
        conn.close();
    }

    private static void outputResultSet(ResultSet rs) throws Exception {
        ResultSetMetaData rsMetaData = rs.getMetaData();
        int numberOfColumns = rsMetaData.getColumnCount();
        for (int i = 1; i < numberOfColumns + 1; i++) {
            String columnName = rsMetaData.getColumnName(i);
            System.out.print(columnName + "   ");

        }
        System.out.println();
        System.out.println("----------------------");

        String array [] = new String [numberOfColumns + 1];

        while (rs.next()) {
            for (int i = 1; i < numberOfColumns + 1; i++) {
                array[i] = rs.getString(i);
                System.out.println(array[i]);
            }

        }

    }

    private static Connection getConnection() throws Exception {
        Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
        String url = "jdbc:derby:MyDbTest;create=true";
        return DriverManager.getConnection(url);
    }

}

Answer 1

将您声明为私有(private)变量的数组，在静态 block 中对其进行初始化，并为其添加 getter 和 setter 方法。这里没有使用 getter-setter，但这只是为了您的理解。

FruitDatabase.java

public class FruitDatabase {
    private static String[] array;

    public static String[] getArray() {
        return array;
    }

    public static void setArray(String[] arr) {
        array = arr;
    }

    public static void main(String[] args) throws Exception {
    ...
    }

    private static void outputResultSet(ResultSet rs) throws Exception {
    ... 
    while (rs.next()) {
            for (int i = 1; i < numberOfColumns + 1; i++) {
                array[i] = rs.getString(i);
                System.out.println(array[i]);
            }
    setArray(array);
    ....
    }
    ....
}

然后从另一个类(假设 Display.java)中，您需要创建该类的一个对象，然后您可以访问该数组:

Display.java

public class Display {
    public static void main(String[] args) {
        String[] newArr = new String[FruitDatabase.getArray().length];
    int i=0;
    for(String s : FruitDatabase.getArray()){
        System.out.println(s);
            newArr[i++]=s;
    }
    }
}