用jdbc.properties文件配置连接数据库 心得

心得:

容易出现NullPointerException异常,有下列情况:

注意事项:jdbc.properties文件路径问题,可以自己动手写一个properties的类文件,进行测试一下,调用Properties.load(in)方法时,应该行判断一下有没有读取到.,有则下一步.

                Key的名称一定在相同.,

package jdbc.test;

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;


/**
 * 读取jdbc.properties文件并连接数据库

 * 关闭数据库连接

 * 返回Connection的方法
 * 
 * @author Administrator
 * 
 */
public class JDBCProperties {
private String classDriver;
private String url;
private String username;
private String password;
private Connection connection;
private Statement statement;
private ResultSet resultSet;


/**
 * 创建一个空参构造函数加载配置文件 取得参数连接数据库
 * 
 * @return Connection
 * @throws IOException
 * @throws ClassNotFoundException
 */
public JDBCProperties() throws IOException, ClassNotFoundException {

// 输入文件

//路径为当前Classpath的路径.

InputStream inputStream = JDBCProperties.class.getClass()
.getResourceAsStream('/jdbc.properties');
System.out.println(inputStream);
java.util.Properties properties = new java.util.Properties();
if (inputStream != null)
properties.load(inputStream);
// 根据Key取得配置文件中的值
classDriver = properties.getProperty('classDriver');
url = properties.getProperty('url');
username = properties.getProperty('username');
password = properties.getProperty('password');
System.out.println(classDriver);
System.out.println(url);
System.out.println(username);
System.out.println(password);
// 加载类文件
Class.forName(classDriver);


}


/**
 * 
 * 
 * @return
 * @throws SQLException
 */
public java.sql.Connection getConnection() throws SQLException {
return DriverManager.getConnection(url, username, password);
}


/**
 * 关闭数据库连接信息
 */
public void closeConnceiont() {
if (resultSet != null) {
try {
resultSet.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (statement != null) {


try {
statement.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (connection != null) {


try {
connection.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}


}
}

}

测试创建一个表

package jdbc.test;


import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;


public class TestJdbc {
private static String sql = 'create table test(id int)';


public static void main(String[] args) throws Exception {
JDBCProperties jdbcProperties = new JDBCProperties();
Connection connection = jdbcProperties.getConnection();
Statement statement = connection.createStatement();
statement.executeUpdate(sql);
ResultSet resultSet = statement.getResultSet();
if (resultSet != null) {
while (resultSet.next()) {
System.out.println(resultSet.getObject(1));
}
}
}
}

jdbc.properties文件

classDriver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/test
username=root
password=admin