Question

程序two.java正在编译，但没有生成输出，没有异常发生。

（在cmd中执行）

// db.properties

driverclass = oracle.jdbc.driver.OracleDriver
url = jdbc:oracle:thin:@loacalhost:1521:xe
user = system
password = kapil

// ConnectionProvider.java

class ConnectionProvider
{
    static Properties prop;

    static
    {
        prop = new Properties();
        String path = File.separator + "db.properties";
        InputStream in = prop.getClass().getResourceAsStream(path);
        try
        {
            prop.load(in);
        }
        catch(Exception e)
        {
        }
    }

    public static Connection getConnection() throws Exception
    {

        Class.forName(prop.getProperty("driverclass"));
        Connection con = DriverManager.getConnection(
                prop.getProperty("url"),
                prop.getProperty("user"),
                prop.getProperty("password"));

        return con;
    }
}

// two.java
class Two
{
    public static void main(String args[])
    {
        try
        {
            Connection con = ConnectionProvider.getConnection();
            Statement stmt = con.createStatement();
            ResultSet rset = stmt.executeQuery("Select * from Emp ");
            while(rset.next())
            {
                System.out.println(rset.getInt(1) + "\t"
                        + rset.getString(2) + "\t"
                        + rset.getString(3) + "\t"
                        + rset.getInt(4));
            }
            con.close();
        }
        catch(Exception e){}
    }
}

Answer 1

首先不要通过这样做来消耗异常catch(Exception e){}这不是一个好习惯，总是像stacktrace一样打印catch(Exception e){ e.printStacktrace();} 现在，你的代码中的问题是url将其更改为 -

url = jdbc:oracle:thin:@localhost:1521:xe

网址localhost中有拼写错误。

编辑：当您通过cmd执行课程时，我希望课程和db.properties在同一文件夹中尝试类似这样的内容

try {
          prop.load(new FileInputStream("db.properties"));
        } catch (IOException e) {
            e.printStackTrace();
        }

所以完整的ConnectionProvider类看起来像这样

class ConnectionProvider
{
    static Properties prop;
    static
    {
        prop = new Properties();
        try {
            prop.load(new FileInputStream("db.properties"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection() throws Exception
    {

        Class.forName(prop.getProperty("driverclass"));
        Connection con = DriverManager.getConnection(prop.getProperty("url"), prop.getProperty("user"), prop.getProperty("password"));

        return con;
    }
}

现在，在执行课程时，不要忘记在课程路径中包含ojdbc6.jar。您可以从here获取。

Answer 2

没有发生异常，因为您正在捕获它而不是打印它。换句话说，可能会发生异常，但您不打印它。

将其添加到catch区块e.printStackTrace();

此代码：
String path = File.separator + "db.properties";左看似乎没有问题。首先打印出路径以确保指向正确的文件。您可以使用.getCanonicalPath()获取绝对路径。

做这样的事情：

            String filePath = new File("./yourfile.properties").getCanonicalPath();
            FileInputStream fis = new FileInputStream(filePath);
            props.load(fis);

Answer 3

您可以使用BalusC的精彩dao layer tutorial。有一个属性文件加载器，可以满足您的需求。代码摘要如下。

这就是文件dao.properties的样子（更改Oracle Db的jdbc.url和jdbc.driver）：

javabase.jdbc.url = jdbc:mysql://localhost:3306/javabase
javabase.jdbc.driver = com.mysql.jdbc.Driver
javabase.jdbc.username = java
javabase.jdbc.password = d$7hF_r!9Y

属性文件加载器（如上所述，您可以根据需要更改它，注意：这取决于您认为此文件在您的环境中发生变化的频率，如果它每年只更改一次，那么它确实是不值得每次从磁盘加载它，但如果它每天都在变化，那么可能值得添加一个静态方法，它重新加载属性文件并通过某些（预定的）后台作业执行它。）

package com.example.dao;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

/**
 * This class immediately loads the DAO properties file 'dao.properties' once in memory and provides
 * a constructor which takes the specific key which is to be used as property key prefix of the DAO
 * properties file. There is a property getter which only returns the property prefixed with
 * 'specificKey.' and provides the option to indicate whether the property is mandatory or not.
 *
 * @author BalusC
 * @link http://balusc.blogspot.com/2008/07/dao-tutorial-data-layer.html
 */
public class DAOProperties {

    // Constants ----------------------------------------------------------------------------------

    private static final String PROPERTIES_FILE = "dao.properties";
    private static final Properties PROPERTIES = new Properties();

    static {
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        InputStream propertiesFile = classLoader.getResourceAsStream(PROPERTIES_FILE);

        if (propertiesFile == null) {
            throw new DAOConfigurationException(
                "Properties file '" + PROPERTIES_FILE + "' is missing in classpath.");
        }

        try {
            PROPERTIES.load(propertiesFile);
        } catch (IOException e) {
            throw new DAOConfigurationException(
                "Cannot load properties file '" + PROPERTIES_FILE + "'.", e);
        }
    }

    // Vars ---------------------------------------------------------------------------------------

    private String specificKey;

    // Constructors -------------------------------------------------------------------------------

    /**
     * Construct a DAOProperties instance for the given specific key which is to be used as property
     * key prefix of the DAO properties file.
     * @param specificKey The specific key which is to be used as property key prefix.
     * @throws DAOConfigurationException During class initialization if the DAO properties file is
     * missing in the classpath or cannot be loaded.
     */
    public DAOProperties(String specificKey) throws DAOConfigurationException {
        this.specificKey = specificKey;
    }

    // Actions ------------------------------------------------------------------------------------

    /**
     * Returns the DAOProperties instance specific property value associated with the given key with
     * the option to indicate whether the property is mandatory or not.
     * @param key The key to be associated with a DAOProperties instance specific value.
     * @param mandatory Sets whether the returned property value should not be null nor empty.
     * @return The DAOProperties instance specific property value associated with the given key.
     * @throws DAOConfigurationException If the returned property value is null or empty while
     * it is mandatory.
     */
    public String getProperty(String key, boolean mandatory) throws DAOConfigurationException {
        String fullKey = specificKey + "." + key;
        String property = PROPERTIES.getProperty(fullKey);

        if (property == null || property.trim().length() == 0) {
            if (mandatory) {
                throw new DAOConfigurationException("Required property '" + fullKey + "'"
                    + " is missing in properties file '" + PROPERTIES_FILE + "'.");
            } else {
                // Make empty value null. Empty Strings are evil.
                property = null;
            }
        }

        return property;
    }

}

使用属性文件连接到oracle数据库

3 个答案: