無法使用 jdbc 和 tomcat 連接到 postgresql。 拋出命名異常

Question

我想創建一個 Jersey ReST API 並訪問 PostgreSQL 數據庫。 我設置了 Tomcat 8 服務器並嘗試訪問本地 PostgreSQL 服務器，但它不起作用。

我的 context.xml （在文件夾“project_folder/main/webapp/META_INF/”中）看起來像

<Context>
    <Resource name="jdbc/mpmttest"
              auth="Container"
              driverClassName="org.postgresql.Driver"
              url="jdbc:postgresql://localhost:5432/mpm"
              user="postgres"
              password="pw"
              maxActive="15"
              maxIdle="3"/>
</Context>

我將以下內容添加到 web.xml

<resource-ref>
        <description>mpmt-database</description>
        <res-ref-name>jdbc/mpmttest</res-ref-name>
        <res-type>javax.sql.DataSource</res-type>
        <res-auth>Container</res-auth>
</resource-ref>

但是當我嘗試查找數據庫時，我得到了一個 NamingException。

我的源代碼：

public class DatabaseHandler {

    private DataSource standardDatabase = null;

    public DatabaseHandler() {
        try {
            InitialContext initCtx = new InitialContext();
            Context envCtx = (Context) initCtx.lookup("java:comp/env");
            standardDatabase = (DataSource) envCtx.lookup("jdbc/mpmttest");
        } catch (NamingException e) {
            e.printStackTrace();
            throw new RuntimeException("Failed to create datasource for standard binding", e);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public Connection getConnection() throws SQLException
    {
        return standardDatabase.getConnection();
    }

}

瀏覽器中顯示的堆棧跟蹤顯示：

Root Cause

javax.naming.NamingException: Unexpected exception resolving reference [Root exception is java.lang.NullPointerException]
    org.apache.naming.NamingContext.lookup(NamingContext.java:856)
    org.apache.naming.NamingContext.lookup(NamingContext.java:159)
    org.apache.naming.NamingContext.lookup(NamingContext.java:827)
    org.apache.naming.NamingContext.lookup(NamingContext.java:173)
    com.sap.ida.ae.mpmtservices.persistence.db.DatabaseHandler.<init>(DatabaseHandler.java:21)
    com.sap.ida.ae.mpmtservices.persistence.db.StdDatabaseProvider.getDatabaseHandler(StdDatabaseProvider.java:8)
    com.sap.ida.ae.mpmtservices.api.TestCaseAPI.createTable(TestCaseAPI.java:35)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:498)
    org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.lambda$static$0(ResourceMethodInvocationHandlerFactory.java:52)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:124)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:167)
    org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:219)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:79)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:469)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:391)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:80)
    org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:255)
    org.glassfish.jersey.internal.Errors$1.call(Errors.java:248)
    org.glassfish.jersey.internal.Errors$1.call(Errors.java:244)
    org.glassfish.jersey.internal.Errors.process(Errors.java:292)
    org.glassfish.jersey.internal.Errors.process(Errors.java:274)
    org.glassfish.jersey.internal.Errors.process(Errors.java:244)
    org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:265)
    org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:234)
    org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:680)
    org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:394)
    org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:346)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:366)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:319)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:205)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
Root Cause

java.lang.NullPointerException
    org.apache.naming.factory.ResourceFactory.getDefaultFactory(ResourceFactory.java:45)
    org.apache.naming.factory.FactoryBase.getObjectInstance(FactoryBase.java:92)
    javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
    org.apache.naming.NamingContext.lookup(NamingContext.java:839)
    org.apache.naming.NamingContext.lookup(NamingContext.java:159)
    org.apache.naming.NamingContext.lookup(NamingContext.java:827)
    org.apache.naming.NamingContext.lookup(NamingContext.java:173)
    com.sap.ida.ae.mpmtservices.persistence.db.DatabaseHandler.<init>(DatabaseHandler.java:21)
    com.sap.ida.ae.mpmtservices.persistence.db.StdDatabaseProvider.getDatabaseHandler(StdDatabaseProvider.java:8)
    com.sap.ida.ae.mpmtservices.api.TestCaseAPI.createTable(TestCaseAPI.java:35)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:498)
    org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.lambda$static$0(ResourceMethodInvocationHandlerFactory.java:52)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:124)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:167)
    org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:219)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:79)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:469)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:391)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:80)
    org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:255)
    org.glassfish.jersey.internal.Errors$1.call(Errors.java:248)
    org.glassfish.jersey.internal.Errors$1.call(Errors.java:244)
    org.glassfish.jersey.internal.Errors.process(Errors.java:292)
    org.glassfish.jersey.internal.Errors.process(Errors.java:274)
    org.glassfish.jersey.internal.Errors.process(Errors.java:244)
    org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:265)
    org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:234)
    org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:680)
    org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:394)
    org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:346)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:366)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:319)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:205)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

我玩了很多配置和編碼，但沒有解決問題。 似乎無法訪問數據庫。 我可以關閉數據庫服務器並遇到同樣的問題。 我不知道我能做些什么來解決這個問題。

Answer 1

您可以像這樣在 Databasehandler 中嘗試一下嗎：

//Context envCtx = (Context) initCtx.lookup("java:comp/env");
standardDatabase = (DataSource) initCtx.lookup("java:comp/env/jdbc/mpmpttest");

我對所有運行 tomcat 8 和 9 的 Web 應用程序都這樣做