h2 数据库的 ClassNotFound 异常 class.forname("org.h2.Driver")

Question

我无法获取 Class.forname("org.h2.Driver");不抛出异常。我将 h2*.jar 添加到构建文件中，我什至得到了一个主文件来访问数据库（寒冷将在问题代码下。我正在尝试在 Vaadin 应用程序中使用 dbValues，但它只是不接受。我似乎无法导入任何包 org.h2.samples; 或 org.h2.*;

注意：dbValues 通过 Vaadin 项目运行。我不知道这是否有帮助，但这是我能想到的它（不起作用）和 dbTest（起作用）之间的唯一显着区别。

package com.example.assignment3;

import java.sql.*;
import java.util.ArrayList;

public class dbValues {

    ArrayList<business> a = new ArrayList<business>();

    public dbValues(){
        
        business b = new business();
        ArrayList<business> a = new ArrayList<business>();
        
        try {
            Class.forName("org.h2.Driver");
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {
            
            Connection conn = DriverManager.getConnection("jdbc:h2:~/test","Lucas","");
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM COMPANIES");
            while(rs.next()){
                b.setID(rs.getInt("ID"));
                b.setName(rs.getString("NAME"));
                b.setSector(rs.getString("SECTOR"));
                b.setAddress(rs.getString("ADDRESS"));
                b.setProvince(rs.getString("PROVINCE"));
                a.add(b);
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
    }
    
    public ArrayList<business> returnBusinesses(){
        return a;
    }
}

这是似乎有效的代码。这两个在同一个目录中，所以这不是问题。

import java.sql.*;
import java.util.ArrayList;

import com.example.assignment3.business;
public class dbtest {
public static void main(String[] a)
throws Exception {

    /**
     * Create variables to iterate through when adding to database.
     */
    String dbname = "COMPANIES";
    int id = 0;
    String name = "";
    String sector = "";
    String address = "";
    String province = "";
    String query = "";
    
    Class.forName("org.h2.Driver");
    Connection conn = DriverManager.getConnection("jdbc:h2:~/test","Lucas","");
    
    /**
     * Create the business objects.
     */
    business boeing = new business(900162738, "Boeing Canada", "Aerospace", "123 Planes St.", "BC");
    business odysseyMoon = new business(900687789, "Odyssey Moon", "Aerospace", "687 The Moon", "NS");
    business vantage = new business(900278382, "Vantage Airport Group", "Aerospace", "77 Smith St.", "NB");
    business canadaBank = new business(900789213, "Bank of Canada", "Financial Services", "2325 Canada blvd.", "ON");
    business montrealBank = new business(900890876, "Bank of Montreal", "Financial Services", "2132 Bonjour Rd.", "QC");
    business rbc = new business(900564738, "Royal Bank of Canada", "Financial Services", "132 Clifton St.", "NB");
    business ubisoft = new business(900547967, "Ubisoft Halifax", "Interactive Media", "2000 Barrington St.", "NS");
    business scotiaBank = new business(900345273, "Scotia Bank", "Financial Services", "Yahmon Rd.", "NS");
    business propaganda = new business(900101928, "Propaganda Games", "Interactive Media", "25 Queen St.", "NT");
    business ea = new business(900162739, "EA Montreal", "Interactive Media", "54 Gagnon St.", "QC");
    
    /**
     * Create the arraylist that will be iterated through when adding
     * to the database and then add them to that list.
     */
    ArrayList<business> businesses = new ArrayList<business>();
    businesses.add(boeing);
    businesses.add(odysseyMoon);
    businesses.add(vantage);
    businesses.add(canadaBank);
    businesses.add(montrealBank);
    businesses.add(rbc);
    businesses.add(ubisoft);
    businesses.add(scotiaBank);
    businesses.add(propaganda);
    businesses.add(ea);
    
    /**
     * Perform the statement that populates the database.
     */
    try {
        Statement stmt = conn.createStatement();
        for(int i = 0; i < businesses.size(); i++){
            id = businesses.get(i).getID();
            name = businesses.get(i).getName();
            sector = businesses.get(i).getSector();
            address = businesses.get(i).getAddress();
            province = businesses.get(i).getProvince();
            query = "INSERT INTO " + dbname + " VALUES("+ id +", '"+ name +"', '"+ sector +"', '"+ address +"', '"+ province +"');";
            System.out.println(query);
            stmt.execute(query);
        }
        //stmt.execute("DELETE FROM COMPANIES;");

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

那么对这些问题有什么想法吗？我有大约 24 小时的时间来完成这项工作。

Answer 1

确保库位于类路径中。 您可以手动将库包含在 WEB-INF/lib 上。或者，您可以将 H2 jar 包含在 Tomcat 公用 lib 文件夹中。

Answer 2

JDBC 驱动程序以需要放置在 Servlet 容器而不是特定的 Web 应用程序中而闻名（臭名昭著？）。这避免了各种问题。正如this Answer by Reichart 解释的那样：

JDBC 驱动程序在所有 Web 应用程序共享的 JVM 范围的单例 DriverManager 中注册自己。

不幸的是，将您的 JDBC 驱动程序移至 Servlet 容器意味着您在该容器上的所有 Web 应用程序必须使用相同版本的驱动程序，也许还有数据库。

尚不确定这对 H2 意味着什么。但似乎最好将整个 H2 jar 放入 Servlet 容器而不是您的 Web 应用程序。