尝试在我的数据库中读取数据并进行更新，但似乎总是会出现异常。为什么我无法阅读和更新任何内容。我知道我与数据库有联系。我相当确定我的SQL语法在我的java代码中是正确的。程序/ applet没有在浏览器中直接在eclipse中运行，所以这应该可以正常工作。
这是我的代码
public class Kreta1 extends JApplet {
private static final long serialVersionUID = -6464646464646464646;//just some nrs
private Vector card;
private int menu_id;
private String name_dish,price,ingredients,recipe;
private Connectie con;
class Afhaalmenu1{
private Connectie con;
private int menu_id;
private String name_dish,price,ingredients,recipe;
private Vector card;
public Afhaalmenu1(){
con= new Connectie();
card=new Vector();
}
public Afhaalmenu1(int menu_id){
this();
this.menu_id=menu_id;
}
public Afhaalmenu1(int menu_id, String name_dish, String price,String ingredients, String recipe){
this();
this.menu_id=menu_id;
this.name_dish=name_dish;
this.price=price;
this.ingredients=ingredients;
this.recipe=recipe;
}
public void setName_dish (String ng){
this.name_dish=ng;
}
public String getName_dish){
return name_dish;
}
public void setPrice (String pr){
this.price=pr;
}
public String getPrice(){
return price;
}
public void setIngredients(String ingr){
this.ingredients=ingr;
}
public String getIngredients(){
return ingredients;
}
public void setRecipe(String rec){
this.recipe=rec;
}
public String getRecipe(){
return recipe;
}
public void setMenu_id(int I){
this.menu_id=I;
}
public int getMenu_id(){
return menu_id;
}
public void readCard(int menu_id){
try{
java.sql.Statement statement= con.connection.createStatement();
this.menu_id=menu_id;
String gget;
gget="SELECT * FROM afhaalmenu WHERE menu_id= "+ this.menu_id;
ResultSet rs= statement.executeQuery(gget);
rs.next();
this.menu_id=rs.getInt(1);
this.name_dish=rs.getString(2);
this.price= rs.getString(3);
this.ingredients= rs.getString(4);
this.recipe= rs.getString(5);
System.out.println(this.menu_id);
}catch(Exception e){
System.out.println("did not read anything");
}
}
public void updateCard(){
try{
java.sql.Statement statement= con.connection.createStatement();
String sset;
sset= "UPDATE afhaalmenu " + "SET name_dish = '" + name_dish + "', " + "price='" + this.price + "'," +
" ingredients='" + this.ingredients + "'," + "recipe='" + this.recipe+ "'"+ "WHERE afhaalmenu.menu_id = " + this.menu_id;
statement.executeUpdate(sset);
System.out.println();
}catch(Exception e){
System.out.println("did not update anything");
}
}
public void writeCard(){
try{
java.sql.Statement statement =con.connection.createStatement();
String gget;
gget= "SELECT "+this.menu_id+" FROM afhaalmenu";
ResultSet rs =statement.executeQuery(gget);
rs.last();
this.menu_id=(rs.getInt(1))+1;
}catch (Exception e){
System.out.print("display error");
con.displaySQLErrors(e);
}
try{
java.sql.Statement statement= con.connection.createStatement();
String sset;
sset= "INSERT INTO afhaalmenu(menu_id, name_dish, price, ingredients, recipe,) VALUES ('" + this.menu_id + "' ,'"+ this.name_dish + "', '"+ this.price +"','"+this.ingredients + "','" + this.recipe + "');";
//System.out.println(sset);
statement.executeUpdate(sset);
System.out.println(sset);
}catch (Exception e){
System.out.println("error writing to database");
e.printStackTrace();
}
}
@SuppressWarnings("unused")
public Vector readAllCards(){
try{
java.sql.Statement statement= con.connection.createStatement();
String gget;
gget="SELECT FROM afhaalmenu; ";
ResultSet rs= statement.executeQuery(gget);
while (rs.next()){
Vector vRow= new Vector();
for(int x=0;x<=3;x++){
vRow.addElement(rs.getString(x));
}
afhaalKaarten.add(vRow);
}
}catch(Exception e){
//con.displaySQLErrors(e);
System.out.println("all cards can not be read");
}
return card;
}
}
public Kreta1(){
con= new Connectie();
card= new Vector();
}
public void init(){
// gui stuff here
Afhaalmenu1 afm= new Afhaalmenu1();
afm.readCard(1);
afm.setName_dish("turkse pizza");
afm.updateCard();
card=kaart.leesAlleKaarten1();
System.out.println(kaart.leesAlleKaarten1());
}
public void start(){
init();
}
public void stop(){
}
public void destroy(){
}
}
我的连接类，它位于同一个项目中但位于不同的类中（没有从中获取任何错误）：
public class Connectie {
private String host= "localhost";
private String user= "root";
private String password="";
private String databasenaam="kreta";
java.sql.Connection connection;
public void displaySQLErrors( Exception e){
String error;
error="SQL foutmelding; "+ e.getMessage();
JOptionPane.showMessageDialog(null, error, "foutmelding",+
JOptionPane.ERROR_MESSAGE);
}
public Connectie(){
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
}
catch(Exception e){
String error= "Niet mogelijk om de driver te laden";
JOptionPane.showMessageDialog(null, error, "error message",+
JOptionPane.ERROR_MESSAGE);
System.exit(1);
}
try{
connection=DriverManager.getConnection("jdbc:mysql://"+ this.host+ "/"+this.databasenaam+"?user="+ this.user+"&password="+ this.password);
String succes= "there is a connectin with database";
JOptionPane.showMessageDialog(null, succes,"succes",JOptionPane.INFORMATION_MESSAGE);
}
catch(Exception e){
displaySQLErrors(e);
}
}
}
这是我在控制台中获得的内容：
1
did not update anything
all cards can not be read
all cards can not be read
[]
1
did not update anything
all cards can not be read
all cards can not be read
[]
我知道我的代码并不完美，因为我不止一次收到错误消息。我只是想弄清楚为什么检索和更新不起作用。干杯
添加e.printStackTrace（）时;在我的catch方法中，我得到了这个很长的错误：
1 没有更新任何东西
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'FROM afhaalmenu' at line 1
All cards can not be read
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
at com.mysql.jdbc.Util.getInstance(Util.java:387)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:941)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3870)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3806)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2470)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2617)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2546)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2504)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1370)
at Kreta1$Afhaalmenu1.readAllCards(Kreta1.java:174)
at Kreta1.init(Kreta1.java:256)
at sun.applet.AppletPanel.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'FROM afhaalmenu' at line 1
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
at com.mysql.jdbc.Util.getInstance(Util.java:387)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:941)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3870)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3806)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2470)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2617)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2546)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2504)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1370)
at Kreta1$Afhaalmenu1.readALLCards(Kreta1.java:174)
at Kreta1.init(Kreta1.java:257)
at sun.applet.AppletPanel.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
all cards can not be read
[]