Java读取配置文件信息连接数据库
创建java 工程，导入PGsql 驱动包结构如下：

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数据库配置文件内容;

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import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import org.json.JSONException;
import org.json.JSONObject;

public class PGUtil {
public static final String CONFIG_FILE_LOCATION = "/db.properties"; //配置文件路径
private static Connection connection = null;
private static final Properties config = new Properties();

static {
    String propertiesPath = CONFIG_FILE_LOCATION.startsWith("/") ?
            CONFIG_FILE_LOCATION.substring(1) : CONFIG_FILE_LOCATION;
            
    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
    try (InputStream in = classLoader.getResourceAsStream(propertiesPath)){
        if (in != null){
            config.load(in);
            String url = config.getProperty("url");
            String userName = config.getProperty("username");
            String password = config.getProperty("password");
            String driver = "org.postgresql.Driver";  
            try {
                Class.forName(driver); 
                connection = (Connection) DriverManager.getConnection(url, userName, password);
                System.out.println(connection);
            } catch (Exception e) {
                e.printStackTrace();
            }  
        }
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

public static void main(String[] args) {
     JSONObject jsonObject =  new JSONObject();
     String sql = "select * from users_info WHERE user_name = 'admin' AND user_password = 'admin'";
        PreparedStatement pstmt;  
        try {  
            pstmt = (PreparedStatement)connection.prepareStatement(sql);  
            ResultSet rs = pstmt.executeQuery();  
            while (rs.next()) {  
                try {
                    jsonObject.put("user_id", rs.getString("user_id"));
                    jsonObject.put("user_name", rs.getString("user_name"));
                    jsonObject.put("user_department_id", rs.getString("user_department_id"));
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            } 
            System.out.println(jsonObject);
        } catch (SQLException e) {  
             System.err.println(e.getClass().getName() + ": " + e.getMessage());  
             System.exit(0);  
        }  
}