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我正在覆盖 Spring 的 MessageSource 以从数据库（当前 SQLite）获取消息源。

正如您在 CachedMessageSourceDao.java (Subject) 中看到的，每当 insertMessage 调用 CachedMessageSource.java(Observer) 时都会收到通知。因为它是观察者模式！！

除了初始化 CachedMessageSourceDao.java （主题）之外，所有工作正常。

DualKeyMap MESSAGES <--即使一开始没有通知，也应该填写。

但我不知道如何实现。你能告诉我哪种设计模式应该适用于此吗？

应用程序上下文.xml

<bean id="cachedMessageSourceDao" class="org.springframework.context.support.CachedMessageSourceDao">
        <constructor-arg name ="dataSource" ref="dataSource" />
        <constructor-arg name="DATABASE" value="BytoCms"/>
        <constructor-arg name="TABLE" value="MessageSource"/>
        <constructor-arg name="USE" value="1" type="int"/>
        <constructor-arg name="NOT_IN_USE" value="0" type="int"/>
        <constructor-arg name="ALL" value="99" type="int"/>
        <constructor-arg name="messageSource" ref="messageSource" />
    </bean>

    <bean id="messageSource" class="org.springframework.context.support.CachedMessageSource" />

CachedMessageSource.java（观察者）

public class CachedMessageSource implements MessageSource, Observer {

    /** Message Storage */
    private static DualKeyMap<String, Locale, String> MESSAGES;

    ...more

@Override
public void update(Observable o, Object arg) {
    try {
        MESSAGES = ((CachedMessageSourceDao) o).selectAllMessages();
    } catch (SQLException e) {
        System.out.println("Message Initializing Failed");
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

CachedMessageSourceDao.java（主题）

public class CachedMessageSourceDao extends Observable {
    private DataSource dataSource;
    private String DATABASE;
    private String TABLE;
    private int USE;
    private int NOT_IN_USE;
    private int ALL;

    public CachedMessageSourceDao(
            DataSource dataSource, 
            String DATABASE, 
            String TABLE,
            int USE,
            int NOT_IN_USE,
            int ALL,
            CachedMessageSource messageSource) {

        this.dataSource = dataSource;
        this.DATABASE = DATABASE;
        this.TABLE = TABLE;
        this.USE = USE;
        this.ALL = ALL;
        this.NOT_IN_USE = NOT_IN_USE;

        addObserver(messageSource); //★add Observer★
        notifyObservers(); //★This for initializing★
    }

    ...more

    public synchronized void insertMessage(String code, String value, String language) throws Exception {
        //Duplicate Message Check
        if(selectMessage(code, language) != null) throw new SQLException("Duplicate message exists for code: " + code + " and" + "language: " + language);

        String sql = "INSERT INTO " + TABLE + " (code, value, language, flag) values (?, ?, ?, " + USE + ")";

        Connection conn = null;
        PreparedStatement pstmt = null;

        try {
            conn = dataSource.getConnection();
            conn.setAutoCommit(true);
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, code);
            pstmt.setString(2, value);
            pstmt.setString(3, language);
            pstmt.execute();

        } catch(SQLException ex) {

            ex.printStackTrace();

        } finally {

            try {

                if(pstmt != null) pstmt.close();
                if(conn != null) conn.close();

            } catch (SQLException e) {

                e.printStackTrace();

            }

        }
        notifyObservers(); //Realtime apply to MessageSource
    }
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