为什么准备好的语句在 java 中不起作用？
Why the prepared statement not working in java?
我正在尝试通过提供来自 db 的卷号和介质来获取学生信息。 swing 应用程序执行时没有任何错误，但是当我输入 roll no 和 medium 时，它会进入 "Student not Found" else 循环。
我想 get string 或准备好的问题 statements.kindly 帮助我找出问题所在。
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.sql.*;
public class Searchdb extends JFrame implements ActionListener {
//Initializing Components
JLabel lb,lbd,lb1, lb2, lb3, lb5;
JTextField tf1, tf2,tf3,tf5,tfd;
JButton btn;
//Creating Constructor for initializing JFrame components
Searchdb() {
//Providing Title
super("Fetching Roll Information");
lb5 = new JLabel("Roll Number:");
lb5.setBounds(20, 20, 100, 20);
tf5 = new JTextField(20);
tf5.setBounds(130, 20, 200, 20);
lbd = new JLabel("Date:");
lbd.setBounds(20, 50, 100, 20);
tfd = new JTextField(20);
tfd.setBounds(130, 50, 200, 20);
btn = new JButton("Submit");
btn.setBounds(50, 50, 100, 20);
btn.addActionListener(this);
lb = new JLabel("Fetching Student Information From Database");
lb.setBounds(30, 80, 450, 30);
lb.setForeground(Color.black);
lb.setFont(new Font("Serif", Font.PLAIN, 12));
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(500, 500);
lb1 = new JLabel("Name:");
lb1.setBounds(20, 120, 100, 20);
tf1 = new JTextField(50);
tf1.setBounds(130, 120, 200, 20);
lb2 = new JLabel("Fathername:");
lb2.setBounds(20, 150, 100, 20);
tf2 = new JTextField(100);
tf2.setBounds(130, 150, 200, 20);
lb3 = new JLabel("State:");
lb3.setBounds(20, 180, 100, 20);
tf3 = new JTextField(50);
tf3.setBounds(130, 180, 200, 20);
setLayout(null);
//Add components to the JFrame
add(lb5);
add(tf5);
add(lbd);
add(tfd);
add(btn);
add(lb);
add(lb1);
add(tf1);
add(lb2);
add(tf2);
add(lb3);
add(tf3);
//Set TextField Editable False
tf1.setEditable(false);
tf2.setEditable(false);
tf3.setEditable(false);
}
public void actionPerformed(ActionEvent e) {
//Create DataBase Coonection and Fetching Records
try {
String str = tf5.getText();
Datestri = tfd.getText();//Getting the unable to convert String to Date error
System.out.println(str);
System.out.println(stri);
Class.forName("oracle.jdbc.driver.OracleDriver");
Connection con = DriverManager.getConnection("jdbc:oracle:thin:@//host:port/servicename","username","password");
PreparedStatement st = con.prepareStatement("select Name,Fathername,State from student_db where roll_number=? and medium=?");
System.out.println(st);
st.setString(1, str);
st.setDate(2, stri);
//Excuting Query
ResultSet rs = st.executeQuery();
System.out.println(rs);
if (rs.next()) {
String s = rs.getString(1);
String s1 = rs.getString(2);
String s2 = rs.getString(3);
//Sets Records in TextFields.
tf1.setText(s);
tf2.setText(s1);
tf3.setText(s2);
} else {
JOptionPane.showMessageDialog(null, "Student not Found");
}
//Create Exception Handler
} catch (Exception ex) {
System.out.println(ex);
}
}
//Running Constructor
public static void main(String args[]) {
new Searchdb();
}
}
sql查询：
select Name,Fathername,State from student_db where roll_number='1441' and medium='2016-12-18';
结果：
Name Fathername State
SA TH YA
假设我没有在查询中传递 "Stri" 变量，我得到了结果。
我已经更新了下面的代码并且它工作正常，当我检查数据库类型的中列名称时它是 varchar2(40)，所以我决定只使用 getString。
使用此代码获得正确响应，
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.sql.*;
public class Searchdb extends JFrame implements ActionListener {
//Initializing Components
JLabel lb,lbd,lb1, lb2, lb3, lb5;
JTextField tf1, tf2,tf3,tf5,tfd;
JButton btn;
//Creating Constructor for initializing JFrame components
Searchdb() {
//Providing Title
super("Fetching Roll Information");
lb5 = new JLabel("Roll Number:");
lb5.setBounds(20, 20, 100, 20);
tf5 = new JTextField(20);
tf5.setBounds(130, 20, 200, 20);
lbd = new JLabel("Date:");
lbd.setBounds(20, 50, 100, 20);
tfd = new JTextField(20);
tfd.setBounds(130, 50, 200, 20);
btn = new JButton("Submit");
btn.setBounds(50, 50, 100, 20);
btn.addActionListener(this);
lb = new JLabel("Fetching Student Information From Database");
lb.setBounds(30, 80, 450, 30);
lb.setForeground(Color.black);
lb.setFont(new Font("Serif", Font.PLAIN, 12));
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(500, 500);
lb1 = new JLabel("Name:");
lb1.setBounds(20, 120, 100, 20);
tf1 = new JTextField(50);
tf1.setBounds(130, 120, 200, 20);
lb2 = new JLabel("Fathername:");
lb2.setBounds(20, 150, 100, 20);
tf2 = new JTextField(100);
tf2.setBounds(130, 150, 200, 20);
lb3 = new JLabel("State:");
lb3.setBounds(20, 180, 100, 20);
tf3 = new JTextField(50);
tf3.setBounds(130, 180, 200, 20);
setLayout(null);
//Add components to the JFrame
add(lb5);
add(tf5);
add(lbd);
add(tfd);
add(btn);
add(lb);
add(lb1);
add(tf1);
add(lb2);
add(tf2);
add(lb3);
add(tf3);
//Set TextField Editable False
tf1.setEditable(false);
tf2.setEditable(false);
tf3.setEditable(false);
}
public void actionPerformed(ActionEvent e) {
//Create DataBase Coonection and Fetching Records
try {
String str = tf5.getText();
String stri = tfd.getText();
System.out.println(str);
System.out.println(stri);
Class.forName("oracle.jdbc.driver.OracleDriver");
Connection con = DriverManager.getConnection("jdbc:oracle:thin:@//host:port/servicename","username","password");
String str1 ="select Name,Fathername,State from student_db where roll_number='"+str+"' and medium='"+stri+"'";
PreparedStatement st = con.prepareStatement(str1);
System.out.println(st);
st.setString(1, str);
st.setString(2, stri);
//Excuting Query
ResultSet rs = st.executeQuery();
System.out.println(rs);
if (rs.next()) {
String s = rs.getString(1);
String s1 = rs.getString(2);
String s2 = rs.getString(3);
//Sets Records in TextFields.
tf1.setText(s);
tf2.setText(s1);
tf3.setText(s2);
} else {
JOptionPane.showMessageDialog(null, "Student not Found");
}
//Create Exception Handler
} catch (Exception ex) {
System.out.println(ex);
}
}
//Running Constructor
public static void main(String args[]) {
new Searchdb();
}
}
我正在尝试通过提供来自 db 的卷号和介质来获取学生信息。 swing 应用程序执行时没有任何错误，但是当我输入 roll no 和 medium 时，它会进入 "Student not Found" else 循环。
我想 get string 或准备好的问题 statements.kindly 帮助我找出问题所在。
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.sql.*;
public class Searchdb extends JFrame implements ActionListener {
//Initializing Components
JLabel lb,lbd,lb1, lb2, lb3, lb5;
JTextField tf1, tf2,tf3,tf5,tfd;
JButton btn;
//Creating Constructor for initializing JFrame components
Searchdb() {
//Providing Title
super("Fetching Roll Information");
lb5 = new JLabel("Roll Number:");
lb5.setBounds(20, 20, 100, 20);
tf5 = new JTextField(20);
tf5.setBounds(130, 20, 200, 20);
lbd = new JLabel("Date:");
lbd.setBounds(20, 50, 100, 20);
tfd = new JTextField(20);
tfd.setBounds(130, 50, 200, 20);
btn = new JButton("Submit");
btn.setBounds(50, 50, 100, 20);
btn.addActionListener(this);
lb = new JLabel("Fetching Student Information From Database");
lb.setBounds(30, 80, 450, 30);
lb.setForeground(Color.black);
lb.setFont(new Font("Serif", Font.PLAIN, 12));
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(500, 500);
lb1 = new JLabel("Name:");
lb1.setBounds(20, 120, 100, 20);
tf1 = new JTextField(50);
tf1.setBounds(130, 120, 200, 20);
lb2 = new JLabel("Fathername:");
lb2.setBounds(20, 150, 100, 20);
tf2 = new JTextField(100);
tf2.setBounds(130, 150, 200, 20);
lb3 = new JLabel("State:");
lb3.setBounds(20, 180, 100, 20);
tf3 = new JTextField(50);
tf3.setBounds(130, 180, 200, 20);
setLayout(null);
//Add components to the JFrame
add(lb5);
add(tf5);
add(lbd);
add(tfd);
add(btn);
add(lb);
add(lb1);
add(tf1);
add(lb2);
add(tf2);
add(lb3);
add(tf3);
//Set TextField Editable False
tf1.setEditable(false);
tf2.setEditable(false);
tf3.setEditable(false);
}
public void actionPerformed(ActionEvent e) {
//Create DataBase Coonection and Fetching Records
try {
String str = tf5.getText();
Datestri = tfd.getText();//Getting the unable to convert String to Date error
System.out.println(str);
System.out.println(stri);
Class.forName("oracle.jdbc.driver.OracleDriver");
Connection con = DriverManager.getConnection("jdbc:oracle:thin:@//host:port/servicename","username","password");
PreparedStatement st = con.prepareStatement("select Name,Fathername,State from student_db where roll_number=? and medium=?");
System.out.println(st);
st.setString(1, str);
st.setDate(2, stri);
//Excuting Query
ResultSet rs = st.executeQuery();
System.out.println(rs);
if (rs.next()) {
String s = rs.getString(1);
String s1 = rs.getString(2);
String s2 = rs.getString(3);
//Sets Records in TextFields.
tf1.setText(s);
tf2.setText(s1);
tf3.setText(s2);
} else {
JOptionPane.showMessageDialog(null, "Student not Found");
}
//Create Exception Handler
} catch (Exception ex) {
System.out.println(ex);
}
}
//Running Constructor
public static void main(String args[]) {
new Searchdb();
}
}
sql查询：
select Name,Fathername,State from student_db where roll_number='1441' and medium='2016-12-18';
结果：
Name Fathername State
SA TH YA
假设我没有在查询中传递 "Stri" 变量，我得到了结果。
我已经更新了下面的代码并且它工作正常，当我检查数据库类型的中列名称时它是 varchar2(40)，所以我决定只使用 getString。
使用此代码获得正确响应，
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.sql.*;
public class Searchdb extends JFrame implements ActionListener {
//Initializing Components
JLabel lb,lbd,lb1, lb2, lb3, lb5;
JTextField tf1, tf2,tf3,tf5,tfd;
JButton btn;
//Creating Constructor for initializing JFrame components
Searchdb() {
//Providing Title
super("Fetching Roll Information");
lb5 = new JLabel("Roll Number:");
lb5.setBounds(20, 20, 100, 20);
tf5 = new JTextField(20);
tf5.setBounds(130, 20, 200, 20);
lbd = new JLabel("Date:");
lbd.setBounds(20, 50, 100, 20);
tfd = new JTextField(20);
tfd.setBounds(130, 50, 200, 20);
btn = new JButton("Submit");
btn.setBounds(50, 50, 100, 20);
btn.addActionListener(this);
lb = new JLabel("Fetching Student Information From Database");
lb.setBounds(30, 80, 450, 30);
lb.setForeground(Color.black);
lb.setFont(new Font("Serif", Font.PLAIN, 12));
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(500, 500);
lb1 = new JLabel("Name:");
lb1.setBounds(20, 120, 100, 20);
tf1 = new JTextField(50);
tf1.setBounds(130, 120, 200, 20);
lb2 = new JLabel("Fathername:");
lb2.setBounds(20, 150, 100, 20);
tf2 = new JTextField(100);
tf2.setBounds(130, 150, 200, 20);
lb3 = new JLabel("State:");
lb3.setBounds(20, 180, 100, 20);
tf3 = new JTextField(50);
tf3.setBounds(130, 180, 200, 20);
setLayout(null);
//Add components to the JFrame
add(lb5);
add(tf5);
add(lbd);
add(tfd);
add(btn);
add(lb);
add(lb1);
add(tf1);
add(lb2);
add(tf2);
add(lb3);
add(tf3);
//Set TextField Editable False
tf1.setEditable(false);
tf2.setEditable(false);
tf3.setEditable(false);
}
public void actionPerformed(ActionEvent e) {
//Create DataBase Coonection and Fetching Records
try {
String str = tf5.getText();
String stri = tfd.getText();
System.out.println(str);
System.out.println(stri);
Class.forName("oracle.jdbc.driver.OracleDriver");
Connection con = DriverManager.getConnection("jdbc:oracle:thin:@//host:port/servicename","username","password");
String str1 ="select Name,Fathername,State from student_db where roll_number='"+str+"' and medium='"+stri+"'";
PreparedStatement st = con.prepareStatement(str1);
System.out.println(st);
st.setString(1, str);
st.setString(2, stri);
//Excuting Query
ResultSet rs = st.executeQuery();
System.out.println(rs);
if (rs.next()) {
String s = rs.getString(1);
String s1 = rs.getString(2);
String s2 = rs.getString(3);
//Sets Records in TextFields.
tf1.setText(s);
tf2.setText(s1);
tf3.setText(s2);
} else {
JOptionPane.showMessageDialog(null, "Student not Found");
}
//Create Exception Handler
} catch (Exception ex) {
System.out.println(ex);
}
}
//Running Constructor
public static void main(String args[]) {
new Searchdb();
}
}