我正在桌面应用程序中工作，我需要连接到数据库以检索一些数据并生成报告。出于测试目的，我在Derby中创建了一个测试数据库，其中包含我需要的表和一些虚拟数据。
由于它是一个小应用程序，我决定使用普通的JDBC使其尽可能轻量级。
我正在使用TDD进行开发。我已经测试了从文件加载连接属性的方法以及创建与DB连接的方法。在尝试查询数据并填充映射到该数据的对象时，我遇到了困难。这是我的代码：
public class JdbcManager {
static final String JDBC_DRIVER_PROPERTY = "jdbc.driver";
static final String JDBC_URL_PROPERTY = "jdbc.url";
static final String JDBC_USER_PROPERTY = "jdbc.username";
static final String JDBC_PASSWORD_PROPERTY = "jdbc.password";
static String PROPERTIES_FILE_PATH = "src/main/resources/connection.properties";
String queryCareers = "SELECT career, name FROM db_career”;
private static final Logger LOG = Logger.getLogger(JdbcManager.class.getName());
public List<Career> getCareerList() {
List<Career> result = new ArrayList<>();
Career item;
Connection connection = createConnection(PROPERTIES_FILE_PATH);
try {
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery(queryCareers);
while (rs.next()) {
item = new Career(rs.getString("Career"), rs.getString("name"));
result.add(item);
}
} catch (SQLException ex) {
LOG.log(Level.SEVERE, “Error retrieving Career data”, ex);
}
return result;
}
// This method is working correctly according to my tests
Connection createConnection(String configFilePath) {
Properties connectionProperties = loadPropertiesFromFile(configFilePath);
try {
Class driverClass = Class.forName(connectionProperties.getProperty(JDBC_DRIVER_PROPERTY));
LOG.log(Level.INFO, "Driver loaded: {0}", driverClass);
} catch (ClassNotFoundException ex) {
LOG.log(Level.SEVERE, "Driver not found”, ex);
}
try (Connection connection = DriverManager.getConnection(
connectionProperties.getProperty(JDBC_URL_PROPERTY),
connectionProperties.getProperty(JDBC_USER_PROPERTY),
connectionProperties.getProperty(JDBC_PASSWORD_PROPERTY))) {
LOG.log(Level.INFO, “Connection created: {0}", connection);
return connection;
} catch (SQLException ex) {
LOG.log(Level.SEVERE, “Unable to connect to DB”, ex);
return null;
}
}
// This method is working correctly according to my tests
Properties loadPropertiesFromFile(String configFilePath) {
File configFile = new File(configFilePath);
Properties properties = new Properties();
try {
properties.load(new FileInputStream(configFile));
LOG.log(Level.INFO, “Properties loaded: {0}", properties);
} catch (FileNotFoundException ex) {
LOG.log(Level.SEVERE, "File not found", ex);
} catch (IOException ex) {
LOG.log(Level.SEVERE, "Error reading the file", ex);
}
return properties;
}
}
然后我有失败的测试：
@Test
public void testGetCareerList() {
logger.log(Level.INFO, "testGetCareerList():");
List<Career> expectedResult = Arrays.asList(
new Career("LGU", “Some dummy name 1”),
new Career("TSGU", "Some dummy name 2”));
// Change the location of the properties file to the testing one
GestorJdbc.PROPERTIES_FILE_PATH = "src/test/resources/connectionTest.properties";
List<Career> actualResult = jdbcManager.getCareerList();
assertEquals(expectedResult, actualResult);
}
最后执行测试时的堆栈跟踪：
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running ar.edu.unt.jdbc.JdbcManagerTest
jun 06, 2017 7:57:24 PM ar.edu.unt.jdbc.JdbcManagerTest testGetCareerList
INFO: testGetCareerList():
jun 06, 2017 7:57:24 PM ar.edu.unt.jdbc.JdbcManager loadPropertiesFromFile
INFO: Properties loaded: {jdbc.url=jdbc:derby://localhost:1527/siu_test, jdbc.username=dba, jdbc.driver=org.apache.derby.jdbc.ClientDriver, jdbc.password=dba}
jun 06, 2017 7:57:24 PM ar.edu.unt.jdbc.JdbcManager createConnection
INFO: Driver loaded: class org.apache.derby.jdbc.ClientDriver
jun 06, 2017 7:57:26 PM ar.edu.unt.jdbc.JdbcManager createConnection
INFO: Connection created: org.apache.derby.client.net.NetConnection40@dc24521
jun 06, 2017 7:57:26 PM ar.edu.unt.jdbc.JdbcManager getCareerList
SEVERE: Error retrieving Career data
java.sql.SQLNonTransientConnectionException: No current connection.
at org.apache.derby.client.am.SQLExceptionFactory40.getSQLException(Unknown Source)
at org.apache.derby.client.am.SqlException.getSQLException(Unknown Source)
at org.apache.derby.client.am.Connection.createStatement(Unknown Source)
at ar.edu.unt.jdbc.JdbcManager.getCareerList(JdbcManager.java:49)
at ar.edu.unt.jdbc.JdbcManagerTest.testGetCareerList(JdbcManagerTest.java:71)
...
我正在使用Netbeans，我有一个正在运行的Derby DB，我可以连接到（正如我所说，连接工作正常）。正如您在堆栈跟踪中看到的那样，createStatement()中会抛出异常，但我找不到原因。
我一直在博客和帖子中潜水，但没有任何对我有用。在一些其他论坛中有一篇文章，用户通过调用Thread.isInterrupted()解决了他的问题，因为createStatement()已同步但对我不起作用，因为我在整个应用程序中使用单个线程（在事实上，它必须是一个旧帖子，因为该方法似乎在Java 8中不可用，只是一个名为Thread.interrupted()的类似方法或类似的方法。）
如果您需要有关我的申请的更多信息，请在评论中告诉我。任何帮助和/或指导都表示赞赏。
答案 0 :(得分：3)
您的方法createConnection正在返回已关闭的连接。您正在使用try-with-resources语句来创建连接。这意味着该连接将在该块退出时自动关闭，无论它是如何退出的（例外，通过返回或刚刚结束）。
当您随后尝试创建语句时，驱动程序会报告您没有连接（尽管错误消息本身可能更清晰一些）。
简而言之，您应该将createConnection更改为：
Connection createConnection(String configFilePath) {
Properties connectionProperties = loadPropertiesFromFile(configFilePath);
try {
Class driverClass = Class.forName(connectionProperties.getProperty(JDBC_DRIVER_PROPERTY));
LOG.log(Level.INFO, "Driver loaded: {0}", driverClass);
} catch (ClassNotFoundException ex) {
LOG.log(Level.SEVERE, "Driver not found”, ex);
}
try {
Connection connection = DriverManager.getConnection(
connectionProperties.getProperty(JDBC_URL_PROPERTY),
connectionProperties.getProperty(JDBC_USER_PROPERTY),
connectionProperties.getProperty(JDBC_PASSWORD_PROPERTY))
LOG.log(Level.INFO, “Connection created: {0}", connection);
return connection;
} catch (SQLException ex) {
LOG.log(Level.SEVERE, “Unable to connect to DB”, ex);
return null;
}
}
BTW：对异常返回null实际上是在其他地方要求NullPointerException。考虑抛出SQLException或创建自己的例外。
另一方面，在getCareerList中你没有使用try-with-resource，而你应该这样做，因为一旦你用createConnection修复了问题，你就会因为没有关闭资源而泄漏资源正确地在getCareerList。将其更改为：
try (Connection connection = createConnection(PROPERTIES_FILE_PATH);
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery(queryCareers)) {
//... rest
} catch (SQLException e) {
//... rest
}
使用此结果集，语句和连接将始终正确关闭。