从properties配置文件中连接数据库

r囧r小猫 2022-08-26 13:19 162阅读 0赞

DB.properties内容：

driver=com.mysql.jdbc.Driver
    url=jdbc\:mysql\://localhost\:3306/demo
    userName=root
    password=admin88

Java代码：

package util;
    
    import java.io.IOException;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Statement;
    import java.util.Properties;
    
    public class JDBC {
    	static JDBC j;
    	Properties p;
    	Connection conn;
    	public static JDBC getInstance(){
    		if(j==null){
    			j=new JDBC();
    		}
    		return j;
    	}
    	public JDBC(){
    		//读取配置文件
    		try {
    			p.load(JDBC.class.getResourceAsStream("/DB.properties"));
    			//加载数据库的驱动类
    			Class.forName(p.getProperty("driver"));
    		} catch (IOException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		} catch (ClassNotFoundException e) {
    			// TODO Auto-generated catch block
    			System.out.println("没有驱动");
    			e.printStackTrace();
    		}
    	}
    	public Connection getConnection(){
    		try {
    			if(conn==null||conn.isClosed()){
    				conn=DriverManager.getConnection(p.getProperty("url"),p.getProperty("userName"),p.getProperty("password"));
    				System.out.println("连接成功！");
    			}
    		} catch (SQLException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		return conn;
    	}
    	public void close(Connection conn,Statement stmt,ResultSet rs ){
    			try {
    				if(rs!=null){
    				rs.close();
    				}if(stmt!=null){
    					stmt.close();
    				}if(conn!=null){
    					conn.close();
    				}
    			} catch (SQLException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    	}
    }

疑惑：使用main函数测试会抛出空指针异常

Exception in thread "main" java.lang.NullPointerException
    	at util.JDBC.<init>(JDBC.java:24)
    	at test.ConnTest.main(ConnTest.java:7)

难道只能用junit单元测试么？