在前面兩篇 http://blog.matrix.org.cn/comments/icess/Weblog/use_derby_with_clob_and??文章中,我簡單介紹了如何使用Java DB操作數(shù)據(jù),今天發(fā)現(xiàn)一個(gè)關(guān)于關(guān)閉數(shù)據(jù)庫的問題, 就是在調(diào)用前面例子中的關(guān)閉數(shù)據(jù)庫代碼時(shí)候總是拋出異常 ,后來到文檔里面看看 ,原來在關(guān)閉數(shù)據(jù)庫時(shí)候, Derby總是拋出異常,我還以為是我那個(gè)地方寫錯(cuò)了呢?
以前例子中沒有顯示異常信息 是應(yīng)為 在關(guān)閉數(shù)據(jù)庫的方法中沒有使用 打印異常信息的語句, 如下
public void disconnect() {
??????? if(isConnected) {
??????????? String dbUrl = getDatabaseUrl();
??????????? dbProperties.put("shutdown", "true");
??????????? try {
??????????????? DriverManager.getConnection(dbUrl, dbProperties);
??????????? } catch (SQLException ex) {
??????????? ?//ex.printStackTrace();?? //?前面的例子沒有該句, 如果加上該句,就會看的異常信息
??????????? }
??????????? isConnected = false;
??????? }
??? }
?
所以,當(dāng)大家看到下面的異常時(shí)候,不用擔(dān)心 不是你的代碼寫錯(cuò)了,而是程序正確關(guān)閉數(shù)據(jù)庫的提示(有點(diǎn)違背異常的設(shè)計(jì)初衷哦).
ERROR 08006: Database 'TestClob' shutdown.
?at org.apache.derby.iapi.error.StandardException.newException(Unknown Source)
?at org.apache.derby.impl.jdbc.TransactionResourceImpl.shutdownDatabaseException(Unknown Source)
?at org.apache.derby.impl.jdbc.EmbedConnection.<init>(Unknown Source)
...........
21:10 補(bǔ)充:
使用Java DB的最佳實(shí)踐
Recommended practices
When developing
Derby applications, create a single directory to hold your database or databases. Give this directory a unique name, to help you remember that:
- All databases exist within a system.
- System-wide properties affect the entire system, and persistent system-wide properties live in the system directory.
- You can boot all the databases in the system, and the boot-up times of all databases affect the performance of the system.
- You can preboot databases only if they are within the system. (Databases do not necessarily have to live inside the system directory, but keeping your databases there is the recommended practice.)
- Once you connect to a database, it is part of the current system and thus inherits all system-wide properties.
- Only one instance of Derby can run in a JVM at a single time, and only one instance of Derby should boot a database at one time. Keeping databases in the system directory makes it less likely that you would use more than one instance of Derby.
- The error log is located inside the system directory.