我正在用Java创建一个雇员数据库，但不断收到“ URL不能为null”错误。这是我为主班的代码：
import java.util.Scanner;
import java.sql.SQLException;
import java.io.IOException;
public class Main {
public static void main(String[] args) throws IOException, SQLException, ClassNotFoundException {
Scanner in = new Scanner(System.in);
boolean quit = false;
String input = "";
// SimpleDataSource.init(args[0]);
// Database.createDB();
while (quit == false) {
System.out.println("Choose an Option: A)dd, S)earch, Q)uit");
input = in.next();
if (input.equalsIgnoreCase("a")) {
System.out.println("Choose an Option: E)mployee");
input=in.next();
if (input.equalsIgnoreCase("e")) {
System.out.println("Enter new Employee ID: ");
int EmpID = in.nextInt();
System.out.println("Enter First Name: ");
String fName = in.next();
System.out.println("Enter Last Name: ");
String lName = in.next();
System.out.println("Enter Skill: ");
String skill1 = in.next();
System.out.println("Enter Department ID: ");
String deptID = in.next();
System.out.println("Enter Skill ID: ");
String skillID = in.next();
System.out.println("Enter Employee Email: ");
String empEmail = in.next();
System.out.println("Enter Employee Phone Number: ");
String empPhone = in.next();
System.out.println("Enter Department Title: ");
String depTitle = in.next();
System.out.println("Enter Supervisor's ID: ");
String supID = in.next();
System.out.println("Enter Supervisor's Last Name: ");
String supLName = in.next();
System.out.println("Enter Supervisor's First Name: ");
String supFName = in.next();
Database.addEmployee(EmpID,fName, lName, skill1, deptID, skillID, empEmail, empPhone, depTitle, supID, supLName, supFName);
}
}else if (input.equalsIgnoreCase("s")) {
System.out.println("Choose an Option: E)mployee, S)kill, E)mail");
input=in.next();
if (input.equalsIgnoreCase("e")) {
System.out.println("Enter Employee ID: ");
int id = in.nextInt();
Database.findEmployee(id);
} else if (input.equalsIgnoreCase("s")) {
System.out.println("Enter Skill: ");
String empSkill1= null;
Database.findSkill(empSkill1);
}
} else if (input.equalsIgnoreCase("e")) {
System.out.println("Enter Employee Email: ");
String empEmail=in.next();
Database.findEmail(empEmail);
} else if (input.equalsIgnoreCase("q")) {
quit = true;
}
}
in.close();
}
}
这是创建数据库的类：
import java.sql.Connection;
import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
public class Database {
static int EmployeeID = 000000001;
/**
* Creates Database
* @throws SQLException
*/
public static void createDB() throws SQLException {
try (Connection conn = SimpleDataSource.getConnection()) {
Statement stat = conn.createStatement();
stat.execute("CREATE TABLE Employees (EmployeeID VARCHAR(9), EmployeeFName VARCHAR(15), EmployeeLName VARCHAR(15), Skill1 VARCHAR(30), DepartmentID CHAR(2), SkillID CHAR(4), Email VARCHAR(40), Phone CHAR(10)");
stat.execute("INSERT INTO Employees VALUES (000000001, 'Bob', 'Ross', ???, ???, ???)");
stat.execute("INSERT INTO Employees VALUES (000000002, 'Chuck', 'Brown', ???, ???, ???)");
stat.execute("INSERT INTO Employees VALUES (000000003, 'Charles', 'Fischer', ???, ???, ???)");
conn.close();
}
}
/**
* Adds a customer to database using given information
* @param cFname First Name
* @param cLname Last name
* @param Skill1 Skill 1
* @param Skill2 Skill 2
* @param Skill3 Skill 3
* @throws SQLException
*/
public static void addEmployee(int EmpID, String EmpFname, String EmpLname, String sk1, String deptID, String skillID, String email, String phoneNum, String depTitle, String supID, String supLName, String supFName) throws SQLException {
try (Connection conn = SimpleDataSource.getConnection()) {
Statement stat = conn.createStatement();
stat.execute("INSERT INTO Customers VALUES (" + EmployeeID + ", '" + EmpFname + "', '" + EmpLname + "', '"
+ sk1 + ","+deptID+","+skillID+","+email+","+phoneNum+","+depTitle+","+supID+","+supLName+","+supFName+",");
conn.close();
}
}
/**
* Increases loyalty value of given customer
* @param CustID Customer ID
* @throws SQLException
*/
/**
* Adds Employee to database using given info
* @param itemName Item Name
* @param price Item Price
* @throws SQLException
*/
/**
* Finds Employee information using given ID
* @param EmployeeID Employee ID
* @throws SQLException
*/
public static void findEmployee(int EmpID) throws SQLException {
try (Connection conn = SimpleDataSource.getConnection()) {
Statement stat = conn.createStatement();
String query = "SELECT * FROM Employee WHERE EmployeeID = " + EmployeeID;
ResultSet result = stat.executeQuery(query);
while (result.next()) {
for (int i = 1; i <= 9; i++) {
System.out.print(result.getString(i) + " ");
}
System.out.println();
}
conn.close();
}
}
/**
* Finds Skill information using given Skill
* @param Skill1 Skill 1
* @param Skill2 Skill 2
* @param Skill3 Skill 3
* @throws SQLException
*/
public static void findSkill(String sk1) throws SQLException {
try (Connection conn = SimpleDataSource.getConnection()) {
Statement stat = conn.createStatement();
String query = "SELECT * FROM Employees WHERE Skill1 ='"+sk1+"";
ResultSet result = stat.executeQuery(query);
while (result.next()) {
for (int i = 1; i <= 4; i++) {
System.out.print(result.getString(i) + " ");
}
System.out.println();
}
conn.close();
}
}
public static void findEmail(String email) throws SQLException {
try (Connection conn = SimpleDataSource.getConnection()) {
Statement stat = conn.createStatement();
String query = "SELECT * FROM Employee WHERE Email = " + email;
ResultSet result = stat.executeQuery(query);
while (result.next()) {
for (int i = 1; i <= 9; i++) {
System.out.print(result.getString(i) + " ");
}
System.out.println();
}
conn.close();
}
}
}
这是我的联系班：
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;
public class SimpleDataSource {
private static String url;
private static String username;
private static String password;
public static void init(String fileName) throws IOException, ClassNotFoundException
{
Properties props= new Properties();
FileInputStream in = new FileInputStream(fileName);
//fileName= "database.properties.properties";
props.load(in);
String driver = props.getProperty("jdbc.driver");
url = props.getProperty("jdbc.url");
username = props.getProperty("jdbc.username");
if(username == "admin") {username = "";}
password = props.getProperty("jdbc.password");
if (password == "secret" ) {password = "";}
if (driver != null) {Class.forName(driver);}
}
public static Connection getConnection() throws SQLException
{
return DriverManager.getConnection(url, username, password);
}
}
这是我的jdbc database.properties文件：
jdbc.url=jdbc:derby:BigJavaDB;create=true
With other databases, you may need to add entries such as these
jdbc.username=admin
jdbc.password=secret
jdbc.driver=org.apache.derby.jdbc.EmbeddedDriver
这是我收到的错误：
Exception in thread "main" java.sql.SQLException: The url cannot be null
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at SimpleDataSource.getConnection(SimpleDataSource.java:36)
at Database.findEmployee(Database.java:89)
at Main.main(Main.java:77)
目前，我已经尝试了所有方法，需要一些帮助。我已尝试多次调试它，但似乎找不到该错误。有任何帮助或建议吗？
答案 0 :(得分：0)
SimpleDataSource.init（...）从未调用过，因此不会设置url。
关于您发布的代码的一些评论。为什么每种方法都是静态的，为什么不使用任何面向对象编程的原理？我不知道您的Java开发人员经验是什么（不会冒犯）。因此，使用此应用程序模型可能有很好的理由。如果您相对较新，则应检查这些原则。它使您可以编写更多可维护的代码，并减少容易出错的代码。