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[英]how do i store Database connectivity methods of mysql in a java netbeans class and call it whenever i need it in a jFrame
[英]How do I call data from a table in a database into a java class in netbeans?
第一次發帖,如果我的問題有點奇怪,對不起。
因此,我在學校有一個項目,要求我們使用netbeans創建Java類,這將打開一個包含三個選項的窗口:檢查庫存,購買物料和更新庫存。
我們有一個名為stockdata的類,其中包含5種不同物品的詳細信息,供我們在三個類中使用以檢查,購買和更新物品。 我們課程的最新階段要求我們創建一個德比數據庫,並將項目輸入表格中。
我這樣做沒有問題,但是在將表中的項目放回類中使用時遇到了問題。 我們得到了以下代碼,但是即使使用注釋的提示,我也無法正常工作。
package stock;
// Skeleton version of StockData.java that links to a database.
// NOTE: You should not have to make any changes to the other
// Java GUI classes for this to work, if you complete it correctly.
// Indeed these classes shouldn't even need to be recompiled
import java.sql.*; // DB handling package
import java.io.*;
import org.apache.derby.drda.NetworkServerControl;
public class StockData {
private static Connection connection;
private static Statement stmt;
static {
// standard code to open a connection and statement to an Access database
try {
NetworkServerControl server = new NetworkServerControl();
server.start(null);
// Load JDBC driver
Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
//Establish a connection
String sourceURL = "jdbc:derby://localhost:1527/"
+ new File("UserDB").getAbsolutePath() + ";";
connection = DriverManager.getConnection(sourceURL, "use", "use");
stmt = connection.createStatement();
} // The following exceptions must be caught
catch (ClassNotFoundException cnfe) {
System.out.println(cnfe);
} catch (SQLException sqle) {
System.out.println(sqle);
} catch (Exception e) {
System.out.println(e);
}
}
// You could make methods getName, getPrice and getQuantity simpler by using an auxiliary
// private String method getField(String key, int fieldNo) to return the appropriate field as a String
public static String getName(String key) {
try {
// Need single quote marks ' around the key field in SQL. This is easy to get wrong!
// For instance if key was "11" the SELECT statement would be:
// SELECT * FROM Stock WHERE stockKey = '11'
ResultSet res = stmt.executeQuery("SELECT * FROM Stock WHERE stockKey = '" + key + "'");
if (res.next()) { // there is a result
// the name field is the second one in the ResultSet
// Note that with ResultSet we count the fields starting from 1
return res.getString(2);
} else {
return null;
}
} catch (SQLException e) {
System.out.println(e);
return null;
}
}
public static double getPrice(String key) {
// Similar to getName. If no result, return -1.0
return 0;
}
public static int getQuantity(String key) {
// Similar to getName. If no result, return -1
return 0;
}
// update stock levels
// extra is +ve if adding stock
// extra is -ve if selling stock
public static void update(String key, int extra) {
// SQL UPDATE statement required. For instance if extra is 5 and stockKey is "11" then updateStr is
// UPDATE Stock SET stockQuantity = stockQuantity + 5 WHERE stockKey = '11'
String updateStr = "UPDATE Stock SET stockQuantity = stockQuantity + " + extra + " WHERE stockKey = '" + key + "'";
System.out.println(updateStr);
try {
stmt.executeUpdate(updateStr);
} catch (SQLException e) {
System.out.println(e);
}
}
// close the database
public static void close() {
try {
connection.close();
} catch (SQLException e) {
// this shouldn't happen
System.out.println(e);
}
}
}
抱歉,這似乎是一個愚蠢的問題,但是我對Java還是很陌生,並且在取得這一障礙之前一直取得良好進展。
提前致謝!
亞歷克斯
在Google上搜索“ java sql”會提供以下鏈接: https : //docs.oracle.com/javase/tutorial/jdbc/basics/processingsqlstatements.html
從連接中,您可以創建一條語句(可以在鏈接和代碼中找到該語句),然后獲取結果集並使用rs.next()對其進行循環。 那應該讓您開始。
當然,您必須確保驅動程序和數據庫在那里/正在運行,只是說...
在這里,netbeans與數據庫無關。 這是一個基於Java的集成開發環境(IDE),它將幫助您減少語法錯誤。
public void dataAccess(){
try {
String connectionUrl = "suitable connection url as per your database";
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
Class.forName("JDBC driver name as per your database");
con = DriverManager.getConnection(connectionUrl, userName, password);
String SQL = "SQL query as per your criteria";
stmt = con.createStatement();
rs = stmt.executeQuery(query);
while (rs.next()) {
// look into ResultSet api and use method as per your requirement
}
rs.close();
}
catch (Exception e) {
//log error message ;
}
}
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