JDBC 将 JAR 从 $HOME/jre/lib/ext 移动到 Gradle 时出错

Question

我的团队在 $JAVA_HOME/jre/lib/ext/文件夹中有我们应用程序的 com.mysql.jdbc.Driver jar，但我正在尝试删除对 JDK 的这种依赖，以使用 Gradle 创建一个更可重复的构建。

我将驱动程序添加到我的build.gradle中，您可以在依赖项的顶部看到：

dependencies {
        compile group: 'mysql', name: 'mysql-connector-java', version: '5.1.+'
        compile group: 'com.notnoop.apns', name: 'apns', version: '1.0.0.Beta6'
        compile group: 'org.slf4j', name: 'slf4j-api', version: '1.7.21'
        compile group: 'com.google.code.gson', name: 'gson', version: '1.7.2'
        compile group: 'net.sf.jazzy', name: 'jazzy', version: '0.5.2-rtext-1.4.1'
        compile group: 'org.apache.lucene', name: 'com.springsource.org.apache.lucene.search.spell', version: '2.4.1'
        compile group: 'com.rabbitmq', name: 'com.springsource.com.rabbitmq.client', version: '1.8.1'
        compile group: 'com.sun.xml', name: 'com.springsource.com.sun.xml.bind', version: '2.2.0'
        compile group: 'com.sun.xml.rpc', name: 'jaxrpc-impl', version: '1.1.3_01'
        compile group: 'com.rabbitmq', name: 'amqp-client', version: '3.6.5'
        testCompile group: 'junit', name: 'junit', version: '4.11'
        compile group: 'com.mashape.unirest', name: 'unirest-java', version: '1.3.1'
        compile fileTree(dir: 'local_lib', include: '*.jar')
}

从 $JAVA_HOME/jre/lib/ext/中删除 jar 并将其放入 gradle 后，我在尝试访问数据库后在 Catalina 日志中收到此错误：

database.BaseDbao.getConnection - We could not create any connection.
org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot load JDBC driver class 'com.mysql.jdbc.Driver'
    at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1136)
    at org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:880)
    at database.BaseDbao.getConnection(BaseDbao.java:116)
    at database.UserDbao.getAuthorizedResultBean(UserDbao.java:357)
    at database.Dbao.getAuthorizedResultBean(Dbao.java:3635)
    at AuthServlet.doPost(AuthServlet.java:71)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at servlets.filters.servletContextFilter.doFilter(servletContextFilter.java:11)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:264)
    at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1130)
    ... 22 more
Dbao.getAuthorizationResultBean() Error - Cannot load JDBC driver class 'com.mysql.jdbc.Driver'
LoginFailed for :suburbantest:because ::10.0.0.22

任何见解将不胜感激！

Answer 1

您可以在 Tomcat 的配置中定义数据源，而不是将其放入应用程序配置中。

Tomcat 具有类加载器的层次结构。你可以在它的网站上阅读它，但长话短说，有三个有趣的类加载器：JDK 类加载器(引导程序(，Tomcat类加载器(系统(和应用程序的类加载器(实际上还有更多，但让我们让它变得简单(。

当驱动程序的jar放入$JAVA_HOME/jre/lib/ext/时，将其添加到JDK类加载器中。当你把它添加到 tomcat/lib 时，你就把它添加到 Tomcat 类加载器中。当您在应用的 gradle 中定义它时，您可以将其添加到应用程序类加载器中。

由于您案例中的数据源配置位于 Tomcat 的配置中，因此它将仅搜索 JDK 和 Tomcat 的类加载器。

一种解决方案是在应用中定义数据源配置(为什么在 Tomcat 中需要它？您是否有多场使用同一数据源的战争？)