Question

我试图了解JDBC内部，特别是，如果出现以下情况，如何加载我的JDBC驱动程序： 1.我没有使用Class.forName（） 2.检查jdbc.driver系统属性是否返回null。

我尝试检查类路径并将系统属性的完整列表打印到控制台，以按照https://docs.oracle.com/javase/8/docs/api/java/sql/DriverManager.html#registerDriver-java.sql.Driver-和https://db.apache.org/derby/docs/10.4/devguide/cdevdvlp40653.html

进行检查

下面是DBConnection类中的DBConnection构造函数

    `public DBConnection() {
        try {
            this.conn = DriverManager.getConnection(JDBC_URL);
            if (this.conn != null) {
                System.out.println("Connection successful");
            }
        } catch(SQLException sqlex) {
            System.out.println("Connection failed");
        }
    }`

下面是main（）


    public static void main(String[] args) {

        DBConnection dbTest = new DBConnection();

        String sysPropsString = System.getProperties().toString();
        String[] propsArr = sysPropsString.split(",");

        for(String property : propsArr) {
            if (property.contains("class") && property.contains("path") 
                    && (property.contains("derby") || property.contains("drivers")))
                System.out.println(property);
        }
        System.out.println("***********************************");
        String sysDrivers = System.getProperty("jdbc.drivers");
        System.out.println(sysDrivers);
    }

我希望从System.getProperty（）调用OR将derby jdbc驱动程序打印到控制台，或者在类路径的某个位置找到它，但是我什么都看不到。 derby驱动程序如何加载？

下面是输出：

连接成功


java.class.path = /用户/aslotu/eclipse-workspace/Bullhorn/build/classes:/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derbyLocale_cs.jar： /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derbyLocale_de_DE.jar：/Library/Java/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derbyLocale_es。 jar：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derbyLocale_fr.jar：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/ derbyLocale_hu.jar：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derbyLocale_it.jar：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/ lib / derbyLocale_ja_JP.jar：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derbyLocale_ko_KR.jar：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/ db / lib / derbyLocale_pl.jar：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derbyLocale_pt_BR.jar：/ Lib rary / Java / JavaVirtualMachines / jdk1.8.0_121.jdk / Contents / Home / db / lib / derbyLocale_ru.jar：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derbyLocale_zh_CN.jar ：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derbyLocale_zh_TW.jar：/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/db/lib/derby .jar


空

Answer 1

derby.jar包含文件META-INF/services/java.sql.Driver，该文件注册org.apache.derby.jdbc.AutoloadedDriver。

这项工作是因为DriverManager使用ServiceLoader。

没有Class.forName（）或System Properties的JDBC驱动程序如何加载？

1 个答案: