非servlet类读取Web文件

怼烎@ 2022-05-16 06:15 168阅读 0赞

package cn.itcast.dao;
    
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.net.URL;
    import java.util.Properties;
    
    //在web工程的普通java程序中如何读取资源文件
    public class StudentDao {  //servlet
    
        public String get() throws IOException {  //类装载器读
            test1();
            test2();
            return null;
        }
    
        //以下代码在读文件时，可以读到更新后的文件
        public void test2() throws IOException{
    
            ClassLoader loader = StudentDao.class.getClassLoader();
            URL url = loader.getResource("cn/itcast/dao/db.properties");
            String filepath = url.getPath();
    
            FileInputStream in = new FileInputStream(filepath);
            Properties prop = new Properties();  //map
            prop.load(in);
    
            String dburl = prop.getProperty("url");
            String username = prop.getProperty("username");
            String password = prop.getProperty("password");
    
            System.out.println(dburl);
            System.out.println(username);
            System.out.println(password);
        }
    
    
        //以下代码在读文件时，读到不到更新后的文件
        public void test1() throws IOException{
            ClassLoader loader = StudentDao.class.getClassLoader();
            InputStream in = loader.getResourceAsStream("cn/itcast/dao/db.properties");
    
            Properties prop = new Properties();  //map
            prop.load(in);
    
            String url = prop.getProperty("url");
            String username = prop.getProperty("username");
            String password = prop.getProperty("password");
    
            System.out.println(url);
            System.out.println(username);
            System.out.println(password);
    
        }
    
    
        //通过类装载器读文件时，需要注意的问题
        //不能用来读取太大的文件
    
    }