Question

我有这个Java应用程序，我现在正在开发一个模块，它可以从文件中读取和执行SQL语句并输出查询结果。如果我通过其main方法启动模块，它工作正常。我给出了数据库连接设置文件的路径（包括用户，传递，端口等），包含SQL查询的文件的路径以及输出文件的名称。正如我所说，单独启动，它运行正常，连接没有问题，执行查询并输出结果。如果我将其集成到应用程序工作流程中，即使凭据（即数据库连接设置文件）相同，它也无法连接到数据库。我试图在一个线程中包装它，试图搜索我是否需要异步启动连接，但没有任何帮助。 mysql-connector-java-5.1.28在classpath中，一切都很好。我也尝试设置autoReconnect（注释行）但它也失败了。这是创建连接的代码：

    String url = "jdbc:mysql://"+server+":3306/?useCursorFetch=true";
//String url = "jdbc:mysql://"+server+":3306/?autoReconnect=true";

try {
    return DriverManager.getConnection(url, user, password);
} catch (SQLException e1) {
        Logging.outputStackTrace(e1);
        throw new RuntimeException("Cannot connect to DB server: " +  e1.getMessage());

with server = localhost。用户和传递很好，抱歉重复第三次，通过模块的main方法启动连接成功。这是我通过应用程序运行模块时获得的堆栈跟踪：

ERROR: An error occurred : Could not create connection to database server. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
Check the error log for details
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
java.lang.reflect.Constructor.newInstance(Unknown Source)
com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
com.mysql.jdbc.Util.getInstance(Util.java:386)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2575)
com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2311)
com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
java.lang.reflect.Constructor.newInstance(Unknown Source)
com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:347)
java.sql.DriverManager.getConnection(Unknown Source)
java.sql.DriverManager.getConnection(Unknown Source)
org.application.utilities.DBConnection.connectToMySQL(DBConnection.java:144)
org.application.utilities.DBConnection.connect(DBConnection.java:107)
org.application.utilities.RunSQL.run(RunSQL.java:110)
org.application.workflow.Processing.extractData(Processing.java:201)
org.application.workflow.Processing.<init>(Processing.java:73)
org.application.gui.ApiGUI$2.actionPerformed(ApiGUI.java:349)
javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
javax.swing.DefaultButtonModel.setPressed(Unknown Source)
javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
java.awt.Component.processMouseEvent(Unknown Source)
javax.swing.JComponent.processMouseEvent(Unknown Source)
java.awt.Component.processEvent(Unknown Source)
java.awt.Container.processEvent(Unknown Source)
java.awt.Component.dispatchEventImpl(Unknown Source)
java.awt.Container.dispatchEventImpl(Unknown Source)
java.awt.Component.dispatchEvent(Unknown Source)
java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
java.awt.Container.dispatchEventImpl(Unknown Source)
java.awt.Window.dispatchEventImpl(Unknown Source)
java.awt.Component.dispatchEvent(Unknown Source)
java.awt.EventQueue.dispatchEventImpl(Unknown Source)
java.awt.EventQueue.access$200(Unknown Source)
java.awt.EventQueue$3.run(Unknown Source)
java.awt.EventQueue$3.run(Unknown Source)
java.security.AccessController.doPrivileged(Native Method)
java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
java.awt.EventQueue$4.run(Unknown Source)
java.awt.EventQueue$4.run(Unknown Source)
java.security.AccessController.doPrivileged(Native Method)
java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
java.awt.EventQueue.dispatchEvent(Unknown Source)
java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
java.awt.EventDispatchThread.pumpEvents(Unknown Source)
java.awt.EventDispatchThread.pumpEvents(Unknown Source)
java.awt.EventDispatchThread.run(Unknown Source)

为什么会发生这种情况？这是线程相关的问题吗？ GUI的事件管理器可以与它有关吗？数据库没有多个连接或并发连接。只完成一次，完成后才能正常关闭。通过MySQL命令行我也访问我的数据库，我确保服务器每次都在，等等... 谢谢。

Answer 1

我想您忘记提及数据库名称

String url = "jdbc:mysql://"+server+":3306/?useCursorFetch=true";

必须是

String url = "jdbc:mysql://"+server+":3306/DB_NAME?useCursorFetch=true";

Answer 2

行。得到它了。当我通过应用程序运行SQL模块时，我通过

将文件编码设置为ANSI

System.setProperty("file.encoding", "ANSI");

单独运行时并非如此。显然，DriverManager.getConnection（url，user，pass）不会自行设置字符集，以确保它以兼容的字符编码发送请求。也许这应该在java.sql包中修复。

无法使用JDBC连接到MySQL数据库

2 个答案: