【发布时间】：2017-12-18 08:32:18
【问题描述】：
我的 JDBC SQLite 数据库有问题：尝试删除表时，我收到错误消息，指出表已锁定。奇怪的是，我在不同的地方使用相同的代码得到不同的结果。我知道这里已经问过这个问题，但我关闭了所有结果集和（准备好的）语句。
这是我的 OfflineDB.java 文件：
public enum OfflineDB {
UNIQUEINSTANCE;
private Connection conn = null;
private OfflineDB(){
try {
System.out.println("Working Directory = " +
System.getProperty("user.dir"));
conn = DriverManager.getConnection("jdbc:sqlite:" +
System.getProperty("user.dir") + "\\database.db");
setupDB();
} catch (SQLException e) {
System.err.println(e.getMessage());
}
}
public Connection getConnection(){
return conn;
}
public void setupDB(){
Statement stmt = null;
try {
stmt = conn.createStatement();
stmt.closeOnCompletion();
stmt.execute(CREATE_CAR);
stmt.execute(CREATE_DTTS);
stmt.execute(CREATE_CHDT);
stmt.execute(CREATE_USER);
stmt.execute(CREATE_CIRCUIT);
stmt.execute(CREATE_CSD);
stmt.execute(CREATE_DASHBOARD);
stmt.execute(CREATE_ICW);
stmt.execute(CREATE_TILE);
stmt.execute(CREATE_TSD);
stmt.execute(CREATE_ISUPDATED);
stmt.close();
} catch (SQLException ex) {
ex.printStackTrace();
} finally{
try {
stmt.close();
} catch (SQLException | NullPointerException e) {
e.printStackTrace();
}
}
}
public boolean dropTables(){
Statement stmt = null;
try {
stmt = conn.createStatement();
stmt.closeOnCompletion();
stmt.execute(DROP_DTTS);
stmt.execute(DROP_CHDT);
stmt.execute(DROP_TSD);
stmt.execute(DROP_CSD);
stmt.execute(DROP_ICW);
stmt.execute(DROP_CAR);
stmt.execute(DROP_CIRCUIT);
stmt.execute(DROP_DASHBOARD);
stmt.execute(DROP_TILE);
stmt.execute(DROP_USER);
stmt.execute(DROP_ISUPDATED);
stmt.close();
} catch (SQLException ex) {
ex.printStackTrace();
System.out.println(ex.getErrorCode());
return false;
} finally{
try {
stmt.close();
} catch (SQLException | NullPointerException e) {
e.printStackTrace();
}
}
return true;
}
简单：它只是在创建时打开一个连接并存储此连接。
我有这个类的 JUnit 测试，这个测试运行完美：
@Test
public void testDropTables(){
Boolean bool = OfflineDB.UNIQUEINSTANCE.dropTables();
assertTrue(bool);
}
在另一个类中，我尝试运行与此测试相同的代码，但在这里我收到错误消息，指出数据库已锁定：
public boolean syncDatabases(){
if(!checkIsUpdated()) return false;
else{
System.out.println("syncing databases");
if(!OfflineDB.UNIQUEINSTANCE.dropTables()) return false;
}
return true;
}
public boolean checkIsUpdated(){
boolean updateNeeded = false;
//check if the online timestamp is later than the offline
Timestamp online = getLastUpdated(true);
Timestamp offline = getLastUpdated(false);
System.out.println("online: " + online + " offline: " + offline);
if(getLastUpdated(true).after(getLastUpdated(false)))
updateNeeded = true;
return updateNeeded;
}
我还为此编写了一个 JUnit，当我尝试运行测试时，会出现错误，如果我在此之后立即运行上一个测试，这没有问题。
@Test
public void testSyncDatabases() {
System.out.println("syncDatabases");
boolean expResult = true;
boolean result = SyncMapper.UNIQUEINSTANCE.syncDatabases();
assertEquals(expResult, result);
}
错误：
org.sqlite.SQLiteException: [SQLITE_LOCKED] A table in the database is locked (database table is locked)
at org.sqlite.core.DB.newSQLException(DB.java:909)
at org.sqlite.core.DB.newSQLException(DB.java:921)
at org.sqlite.core.DB.execute(DB.java:822)
at org.sqlite.core.CoreStatement.exec(CoreStatement.java:75)
at org.sqlite.jdbc3.JDBC3Statement.execute(JDBC3Statement.java:61)
at Storage.OfflineDB.dropTables(OfflineDB.java:256)
at Persistency.SyncMapper.syncDatabases(SyncMapper.java:56)
at Persistency.SyncMapperTest.testSyncDatabases(SyncMapperTest.java:59)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at junit.framework.JUnit4TestAdapter.run(JUnit4TestAdapter.java:38)
at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.run(JUnitTestRunner.java:535)
at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.launch(JUnitTestRunner.java:1182)
at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.main(JUnitTestRunner.java:1033)
【问题讨论】：