如何使用 JDBC 访问 Tomcat 中的 SQLite 数据库？抛出 UnsatisfiedLinkError答案

【问题标题】：How to access SQLite database in Tomcat using JDBC? UnsatisfiedLinkError thrown如何使用 JDBC 访问 Tomcat 中的 SQLite 数据库？抛出 UnsatisfiedLinkError
【发布时间】：2020-09-06 19:15:24
【问题描述】：

我正在使用 Servlet、JSP、JSTL 技术开发 Web Java 应用程序。我使用 SQLite3 数据库，在 IntelliJ Idea IDE 中开发，使用 Maven 编译项目并在 Tomcat 9.0 中进行测试。

我可以直接访问 SQLite 数据库（使用命令行和 sqlite3 下载库：screenshot）。

当我在 intellij idea 中运行 SQLite 数据库时，我还可以通过 JDBC 作为普通 JavaSE 应用程序访问它：screenshot。

但是当我在 Tomcat 上启动我的 web 项目时，在网页上 ServletException 被 UnsatisfiedLinkError 抛出：

HTTP Status 500 – Internal Server Error
Type Exception Report

Message Servlet execution threw an exception

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

javax.servlet.ServletException: Servlet execution threw an exception
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
Root Cause

java.lang.UnsatisfiedLinkError: 'void org.sqlite.core.NativeDB._open_utf8(byte[], int)'
    org.sqlite.core.NativeDB._open_utf8(Native Method)
    org.sqlite.core.NativeDB._open(NativeDB.java:71)
    org.sqlite.core.DB.open(DB.java:174)
    org.sqlite.core.CoreConnection.open(CoreConnection.java:220)
    org.sqlite.core.CoreConnection.<init>(CoreConnection.java:76)
    org.sqlite.jdbc3.JDBC3Connection.<init>(JDBC3Connection.java:25)
    org.sqlite.jdbc4.JDBC4Connection.<init>(JDBC4Connection.java:24)
    org.sqlite.SQLiteConnection.<init>(SQLiteConnection.java:45)
    org.sqlite.JDBC.createConnection(JDBC.java:114)
    org.sqlite.JDBC.connect(JDBC.java:88)
    org.apache.tomcat.dbcp.dbcp2.DriverConnectionFactory.createConnection(DriverConnectionFactory.java:53)
    org.apache.tomcat.dbcp.dbcp2.PoolableConnectionFactory.makeObject(PoolableConnectionFactory.java:355)
    org.apache.tomcat.dbcp.dbcp2.BasicDataSource.validateConnectionFactory(BasicDataSource.java:116)
    org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:731)
    org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createDataSource(BasicDataSource.java:605)
    org.apache.tomcat.dbcp.dbcp2.BasicDataSource.getConnection(BasicDataSource.java:809)
    model.DAO.getRooms(DAO.java:29)
    servlets.HomepageServlet.doGet(HomepageServlet.java:55)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
Note The full stack trace of the root cause is available in the server logs.

在 tomcat 的 startup.bat 命令行窗口中，我看到：

06-Sep-2020 21:11:37.875 INFO [http-nio-8080-exec-32] org.apache.catalina.core.StandardContext.reload Reloading Context with name [/testProject_war_exploded] has started
06-Sep-2020 21:11:38.352 INFO [http-nio-8080-exec-32] org.apache.jasper.servlet.TldScanner.scanJars At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
06-Sep-2020 21:11:38.375 INFO [http-nio-8080-exec-32] org.apache.catalina.core.StandardContext.reload Reloading Context with name [/testProject_war_exploded] is completed
C:\Dropbox\apache-tomcat-9.0.22\temp\sqlite-3.21.0.1-02fa308c-7c4d-4cfb-93cb-3e46dbaa56a1-sqlitejdbc.dll.lck (Системе не удается найти указанный путь)

（系统找不到指定的路径）

这是抛出异常的方法：

package model;

import org.apache.log4j.Logger;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.sql.DataSource;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class DAO {
    private final Logger log = Logger.getLogger(this.getClass());
    private final String driverName = "org.sqlite.JDBC";

    public List<Room> getRooms() {
        List<Room> rooms = new ArrayList<Room>();
        Connection connection = null;
        try {
            Class.forName(driverName);
            Context ctx = new InitialContext();
            DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/rooms");
            connection = ds.getConnection();
        } catch (ClassNotFoundException e) {
            log.debug("Can't get class. No driver found");
            e.printStackTrace();
        } catch (SQLException e) {
            log.debug("Can't get connection. Incorrect URL");
            e.printStackTrace();
        } catch (NamingException e) {
            log.debug("Can't get Context or Datasource");
            e.printStackTrace();
        } catch (Exception e) {
            log.debug("Some other exception");
            e.printStackTrace();
        }
        try {
            String sql = "SELECT * FROM room";
            Statement statement = connection.createStatement();
            ResultSet rs = statement.executeQuery(sql);
            Room room;
            while (rs.next()) {
                room = new Room();
                room.setName(rs.getString("name"));
                room.setCountryCode(rs.getString("country_code"));
                room.setLightOn(rs.getInt("light_status"));
                rooms.add(room);
                log.debug(room.getName() + " " + room.getCountryCode() + "" + room.isLightOn());
            }
        } catch (SQLException e) {
            log.debug("SQL Exception thrown during select statement");
            e.printStackTrace();
        }
        try {
            connection.close();
        } catch (SQLException e) {
            log.debug("Can't close connection");
            e.printStackTrace();
        }
        return rooms;
    }
}

正是这一行在 Servlet 的异常中写为：model.DAO.getRooms(DAO.java:28)

connection = ds.getConnection();

但是，我在没有 Tomcat 的情况下用于 SQLite 访问检查的这段代码工作正常。所以这让我觉得它完全在“tomcat方面”

import model.Room;
import org.apache.log4j.Logger;

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

public class Main {
    private final Logger log = Logger.getLogger(this.getClass());
    private final String driverName = "org.sqlite.JDBC";
    private final String connectionString = "jdbc:sqlite:rooms.db";

    public void run() {
        List<Room> rooms = new ArrayList<Room>();
        Connection connection = null;
        try {
            Class.forName(driverName);
            connection = DriverManager.getConnection(connectionString);
        } catch (ClassNotFoundException e) {
            log.debug("Can't get class. No driver found");
            e.printStackTrace();
        } catch (SQLException e) {
            log.debug("Can't get connection. Incorrect URL");
            e.printStackTrace();
        }
        try {
            String sql = "SELECT * FROM room";
            Statement statement = connection.createStatement();
            ResultSet rs = statement.executeQuery(sql);
            Room room;
            while (rs.next()) {
                room = new Room();
                room.setName(rs.getString("name"));
                room.setCountryCode(rs.getString("country_code"));
                room.setLightOn(rs.getInt("light_status"));
                rooms.add(room);
                System.out.println(room.getName() + " " + room.getCountryCode() + " " + room.isLightOn());
            }
        } catch (SQLException e) {
            log.debug("SQL Exception thrown during select statement");
            e.printStackTrace();
        }
        try {
            connection.close();
        } catch (SQLException e) {
            log.debug("Can't close connection");
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
        Main app = new Main();
        app.run();
    }
}

为了让 Tomcat 找到我的数据库，我在 web.xml 中创建了资源引用

    <resource-ref>
        <description>Rooms Database</description>
        <res-ref-name>jdbc/rooms</res-ref-name>
        <res-type>javax.sql.DataSource</res-type>
        <res-auth>Container</res-auth>
    </resource-ref>

并且还在 tomcat-dir\conf\Catalina\localhost\testProject_war_exploded.xml 中添加了 Context 标签其中 testProject_war_exploded 是我的应用程序的名称。

<Context reloadable="true" antiJARLocking="true" path="/" docBase="C:\Users\nativ\IdeaProjects\testProject\out\artifacts\testProject_war_exploded\">
    <Resource name="jdbc/rooms"
      auth="Container"
      type="javax.sql.DataSource"
      driverClassName="org.sqlite.JDBC"
      url="jdbc:sqlite:rooms.db">
    </Resource>
</Context>

我也尝试使用相同的代码将具有相同 Context 标记的 context.xml 创建到 /META-INF/context.xml 中。

或者我尝试将 Context 标签添加到 tomcat-dir/conf/server.xml 中的 GlobalNamingResources 标签中 - 我知道不推荐这样做，但仍然没有结果。

我确信 tomcat 会找到该 rooms.db 文件，因为如果我更改路径 - 我会收到 SQLException 和“无法连接。不正确的 URL”写入我的日志文件。

我确定 tomcat 会加载 sqlite3 jar 库，因为我们从 org.sqlite.core 包中抛出了异常。

虽然我很困惑，为什么如果我捕捉到任何异常，我的日志文件中没有来自这个 getRooms() 方法的记录。但是如果我捕获（Throwable），那么我有一个日志文件记录 - 这意味着抛出了一个错误。

在 SQLite 文档中，我发现 a variable 告诉 sqlite 是使用临时文件夹还是内存。我可以更改它via command line，但是 Tomcat 使用 sqlite3 jar 库来打开我的数据库。我应该改变那个罐子里的东西吗？我不知道为什么 tomcat 中的 sqlite3 会尝试访问这个 /temp/... 文件夹。

This isidea 在 \out 目录中创建的我的 Web 项目结构。

这是我的 pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>testProject</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.release>11</maven.compiler.release>
        <junit.jupiter.version>5.6.2</junit.jupiter.version>
    </properties>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>provided</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
            <scope>provided</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/jstl/jstl -->
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-api -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>${junit.jupiter.version}</version>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-engine -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>${junit.jupiter.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <version>${junit.jupiter.version}</version>
            <scope>test</scope>
        </dependency>
        <!-- API for countries' names and codes list -->
        <dependency>
            <groupId>com.neovisionaries</groupId>
            <artifactId>nv-i18n</artifactId>
            <version>1.22</version>
        </dependency>
        <dependency>
            <groupId>com.maxmind.geoip2</groupId>
            <artifactId>geoip2</artifactId>
            <version>2.14.0</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/log4j/log4j -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.xerial/sqlite-jdbc -->
        <dependency>
            <groupId>org.xerial</groupId>
            <artifactId>sqlite-jdbc</artifactId>
            <version>3.21.0.1</version>
        </dependency>
        
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <release>11</release>
                </configuration>
            </plugin>
            <plugin>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.22.2</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-resources-plugin</artifactId>
                <version>3.2.0</version>
                <configuration>
                    <nonFilteredFileExtensions>
                        <nonFilteredFileExtension>exe</nonFilteredFileExtension>
                    </nonFilteredFileExtensions>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

以及处理索引页面的 Servlet 类。

package servlets;

import com.maxmind.geoip2.record.Country;
import com.neovisionaries.i18n.CountryCode;

import controller.LocationHelper;
import model.DAO;
import model.Room;
import org.apache.log4j.Logger;


import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.*;

public class HomepageServlet extends HttpServlet {
    private LocationHelper locationHelper = new LocationHelper();
    private DAO dao = new DAO();
    private final Logger log = Logger.getLogger(this.getClass());

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String roomName = request.getParameter("roomName");
        log.debug("roomName = " + roomName);

        String selectedCountry = request.getParameter("countryList");
        log.debug("selectedCountry = " + selectedCountry);

        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("index.jsp");

        String ipStr = LocationHelper.getClientIpAddr(request);
        request.setAttribute("ipAddress", ipStr);

        String countryStr = "not determined";
        String countrycode = "no code";
        Country country = locationHelper.getCountry(getServletContext());
        if (country != null) {
            countryStr = country.getName();
            countrycode = country.getIsoCode();
        }

        request.setAttribute("country", countryStr);
        request.setAttribute("code", countrycode);

        List<String> countries = getSortedCountriesList();
        request.setAttribute("countriesList", countries);

        List<Room> rooms = dao.getRooms();
        request.setAttribute("roomsList", rooms);

        requestDispatcher.forward(request, response);
    }

    /**
     *
     * @return Sorted countries list to be shown in a dropdown list.
     */
    private List<String> getSortedCountriesList() {
        List<String> countriesList = new ArrayList<>();
        for (CountryCode code : CountryCode.values()) {
            countriesList.add(code.getName());
        }

        Collections.sort(countriesList, (s1, s2) -> s1.compareToIgnoreCase(s2));
        return countriesList;
    }

}

【问题讨论】：

将connection = ds.getConnection(); 替换为connection = DriverManager.getConnection("jdbc:sqlite:rooms.db"); 会发生什么？如果 WEB-INF/lib 有驱动程序 jar，它应该可以工作。
jar 位于 WEB-INF/lib 文件夹中，但它仍然给了我同样的异常。我也将 sqilte jar 直接放入 tomcat/lib 文件夹，但关于 not found \temp\... 文件夹的消息仍然相同

标签： java sqlite tomcat jdbc

【解决方案1】：

您很可能缺少 sqlite-jdbc 所需的本机库。

https://github.com/xerial/sqlite-jdbc/blob/master/src/main/java/org/sqlite/SQLiteJDBCLoader.java#L305

尝试为 jvm 提供 org.sqlite.lib.path 属性，指向 sqlite 共享库的位置。

【讨论】：

我将 sqlite jar 直接放入 tomcat/lib 文件夹中，在数据库访问代码编写 set 属性之前，如下所示：System.setProperty("org.sqlite.lib.path", "${catalina.home}" + "/lib/sqlite-jdbc-3.21.0.1.jar"); 但是当我决定先看看这个属性是什么时，getProperty() 准确地给了我我正在设置的那个字符串。 Servlet 仍然抛出相同的错误，但启动 cmd 没有给出“未找到 /temp/... dir”。相反，它写了 failed to unregistration JDBC driver link 这是否意味着 JDBC driver 已注册，但由于抛出的错误而没有取消注册？

【解决方案2】：

当在 IDE 根文件夹创建连接时，SQLite 将创建一个 DB 文件，要处理这个并指向您的目标 DB，只需使用其完整路径，步骤如下：

将 sqlite-jdbc jar 文件放入 Tomcat\lib 文件夹中
将您的数据库文件 [MyDB.db OR MyDB.sqlite] 放入 Tomcat\lib 文件夹或创建另一个文件夹“db”并在创建 Connection 时使用其完整路径指向它 对象。

【讨论】：