Question

我试图从我的Java代码中创建一个数据库和表无济于事。这是我的数据库代码和运行程序时收到的错误。当我调试PreparedStatement时，变量为null。

public class RecordDao {

/** Creates a new instance of RecordDao */
public RecordDao() {
    this("Requirements");
}

public RecordDao(String requirements) {
    this.dbName = requirements;

    setDBSystemDir();
    dbProperties = loadDBProperties();
    String driverName = dbProperties.getProperty("derby.driver"); 
    loadDatabaseDriver(driverName);
    if(!dbExists()) {
        createDatabase();
    }

}

private boolean dbExists() {
    boolean bExists = false;
    String dbLocation = getDatabaseLocation();
    File dbFileDir = new File(dbLocation);
    if (dbFileDir.exists()) {
        bExists = true;
    }
    return bExists;
}

private void setDBSystemDir() {
    // decide on the db system directory
    String userHomeDir = System.getProperty("user.home", ".");
    String systemDir = userHomeDir + "/.requirementsspecs";
    System.setProperty("derby.system.home", systemDir);

    // create the db system directory
    File fileSystemDir = new File(systemDir);
    fileSystemDir.mkdir();
}

private void loadDatabaseDriver(String driverName) {
    // load Derby driver
    try {
        Class.forName(driverName);
    } catch (ClassNotFoundException ex) {
        ex.printStackTrace();
    }

}

private Properties loadDBProperties() {
    InputStream dbPropInputStream = null;
    dbPropInputStream = RecordDao.class.getResourceAsStream("Configuration.properties");
    dbProperties = new Properties();
    try {
        dbProperties.load(dbPropInputStream);
    } catch (IOException ex) {
        ex.printStackTrace();
    }
    return dbProperties;
}


private boolean createTables(Connection dbConnection) {
    boolean bCreatedTables = false;
    Statement statement = null;
    try {
        statement = dbConnection.createStatement();
        statement.execute(strCreateRequirementsTable);
        bCreatedTables = true;
    } catch (SQLException ex) {
        ex.printStackTrace();
    }

    return bCreatedTables;
}
private boolean createDatabase() {
    boolean bCreated = false;
    Connection dbConnection = null;

    String dbUrl = getDatabaseUrl();
    dbProperties.put("create", "true");

    try {
        System.out.println("inside try statement to create database");
        dbConnection = DriverManager.getConnection(dbUrl, dbProperties);
        bCreated = createTables(dbConnection);
    } catch (SQLException ex) {
    }
    dbProperties.remove("create");
    return bCreated;
}


public boolean connect() {
    String dbUrl = getDatabaseUrl();
    try {
        dbConnection = DriverManager.getConnection(dbUrl, dbProperties);
        stmtSaveNewRecord = dbConnection.prepareStatement(strSaveRecord, Statement.RETURN_GENERATED_KEYS);
        stmtUpdateExistingRecord = dbConnection.prepareStatement(strUpdateRecord);
        stmtGetRecord = dbConnection.prepareStatement(strGetRecord);
        stmtDeleteRecord = dbConnection.prepareStatement(strDeleteRecord);

        isConnected = dbConnection != null;
    } catch (SQLException ex) {
        isConnected = false;
    }
    return isConnected;
}

private String getHomeDir() {
    return System.getProperty("user.home");
}

public void disconnect() {
    if(isConnected) {
        String dbUrl = getDatabaseUrl();
        dbProperties.put("shutdown", "true");
        try {
            DriverManager.getConnection(dbUrl, dbProperties);
        } catch (SQLException ex) {
        }
        isConnected = false;
    }
}

public String getDatabaseLocation() {
    String dbLocation = System.getProperty("derby.system.home") + "/" + dbName;
    return dbLocation;
}

public String getDatabaseUrl() {
    String dbUrl = dbProperties.getProperty("derby.url") + dbName;
    return dbUrl;
}


public int saveRecord(RequirementsData record) {
    int id = -1;
    try {
        stmtSaveNewRecord.clearParameters();
        stmtSaveNewRecord.setString(1, record.getDescription());
        stmtSaveNewRecord.setString(2, record.getType());
        stmtSaveNewRecord.setString(3, record.getStatus());
        stmtSaveNewRecord.setString(4, record.getPriority());
        stmtSaveNewRecord.setString(5, record.getDifficulty());
        stmtSaveNewRecord.setString(6, record.getDueDate());
        stmtSaveNewRecord.setString(7, record.getCreatedOn());
        int rowCount = stmtSaveNewRecord.executeUpdate();
        ResultSet results = stmtSaveNewRecord.getGeneratedKeys();
        if (results.next()) {
            id = results.getInt(1);
        }

    } catch(SQLException sqle) {
        sqle.printStackTrace();
    }
    return id;
}

public boolean editRecord(RequirementsData record) {
    boolean bEdited = false;
    try {
        stmtUpdateExistingRecord.clearParameters();

        stmtUpdateExistingRecord.setString(1, record.getDescription());
        stmtUpdateExistingRecord.setString(2, record.getType());
        stmtUpdateExistingRecord.setString(3, record.getStatus());
        stmtUpdateExistingRecord.setString(4, record.getPriority());
        stmtUpdateExistingRecord.setString(5, record.getDifficulty());
        stmtUpdateExistingRecord.setString(6, record.getDueDate());
        stmtUpdateExistingRecord.setString(7, record.getCreatedOn());
        stmtUpdateExistingRecord.setInt(12, record.getId());
        stmtUpdateExistingRecord.executeUpdate();
        bEdited = true;
    } catch(SQLException sqle) {
        sqle.printStackTrace();
    }
    return bEdited;

}

public boolean deleteRecord(int id) {
    boolean bDeleted = false;
    try {
        stmtDeleteRecord.clearParameters();
        stmtDeleteRecord.setInt(1, id);
        stmtDeleteRecord.executeUpdate();
        bDeleted = true;
    } catch (SQLException sqle) {
        sqle.printStackTrace();
    }

    return bDeleted;
}

public boolean deleteRecord(RequirementsData record) {
    int id = record.getId();
    return deleteRecord(id);
}

public List<ListEntry> getListEntries() {
    List<ListEntry> listEntries = new ArrayList<ListEntry>();
    Statement queryStatement = null;
    ResultSet results = null;

    try {
        queryStatement = dbConnection.createStatement();
        results = queryStatement.executeQuery(strGetListEntries);
        while(results.next()) {
            int id = results.getInt(1);
            String description = results.getString(2);
            String type = results.getString(3);
            String dueDate = results.getString(4);

            ListEntry entry = new ListEntry(description, type, dueDate, id);
            listEntries.add(entry);
        }

    } catch (SQLException sqle) {
        sqle.printStackTrace();

    }

    return listEntries;
}

public RequirementsData getRecord(int index) {
    RequirementsData record = null;
    try {
        stmtGetRecord.clearParameters();
        stmtGetRecord.setInt(1, index);
        ResultSet result = stmtGetRecord.executeQuery();
        if (result.next()) {
            String description = result.getString("DESCRIPTION");
            String type = result.getString("TYPE");
            String status = result.getString("STATUS");
            String priority = result.getString("PRIORITY");
            String difficulty = result.getString("DIFFICULTY");
            String dueDate = result.getString("DUEDATE");
            String createdOn = result.getString("CREATEDON");
            int id = result.getInt("ID");
            record = new RequirementsData(description, type, status, priority,
                    difficulty, dueDate, createdOn, id);
        }
    } catch(SQLException sqle) {
        sqle.printStackTrace();
    }

    return record;
}

public static void main(String[] args) {
    RecordDao db = new RecordDao();
    System.out.println("######"+ db.getDatabaseLocation());
    System.out.println(db.getDatabaseUrl());
    db.connect();
    db.disconnect();
}


private Connection dbConnection;
private Properties dbProperties;
private boolean isConnected;
private String dbName;
private PreparedStatement stmtSaveNewRecord;
private PreparedStatement stmtUpdateExistingRecord;
private PreparedStatement stmtGetListEntries;
private PreparedStatement stmtGetRecord;
private PreparedStatement stmtDeleteRecord;

private static final String strCreateRequirementsTable =
        "create table APP.REQUIREMENTS (" +
        "    ID             INTEGER NOT NULL PRIMARY KEY GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1)," +
        "    DESCRIPTION    VARCHAR(300), " +
        "    TYPE           VARCHAR(15), " +
        "    STATUS         VARCHAR(15), " +
        "    PRIORITY       VARCHAR(15), " +
        "    DIFFICULTY     VARCHAR(15), " +
        "    DUEDATE        VARCHAR(30), " +
        "    CREATEDON      VARCHAR(30), " +
        ")";

private static final String strGetRecord =
        "SELECT * FROM APP.REQUIREMENTS " +
        "WHERE ID = ?";

private static final String strSaveRecord =
        "INSERT INTO APP.REQUIREMENTS " +
        "   (DESCRIPTION, TYPE, STATUS, PRIORITY, DIFFICULTY, DUEDATE, CREATEDON) " +
        "VALUES (?, ?, ?, ?, ?, ?, ?)";


private static final String strGetListEntries =
        "SELECT ID, DESCRIPTION, TYPE, DUEDATE FROM APP.REQUIREMENTS "  +
        "ORDER BY DUEDATE ASC";

private static final String strUpdateRecord =
        "UPDATE APP.REQUIREMENTS " +
        "SET DESCRIPTION = ?, " +
        "    TYPE = ?, " +
        "    STATUS = ?, " +
        "    PRIORITY = ?, " +
        "    DIFFICULTY = ?, " +
        "    DUEDATE = ?, " +
        "    CREATEDON = ?, " +
        "WHERE ID = ?";

private static final String strDeleteRecord =
        "DELETE FROM APP.REQUIREMENTS " +
        "WHERE ID = ?";

}

这是错误：

运行： java.sql.SQLSyntaxErrorException：表/视图'APP.REQUIREMENTS'不存在。 at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException（未知来源）在org.apache.derby.impl.jdbc.Util.generateCsSQLException（未知来源） at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException（未知来源） at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException（未知来源） at org.apache.derby.impl.jdbc.EmbedConnection.handleException（未知来源） at org.apache.derby.impl.jdbc.ConnectionChild.handleException（Unknown Source）在org.apache.derby.impl.jdbc.EmbedStatement.execute（未知来源） at org.apache.derby.impl.jdbc.EmbedStatement.executeQuery（Unknown Source） at com.example.requirements.db.RecordDao.getListEntries（RecordDao.java:240）在com.example.requirements.RequirementsFrame。（RequirementsFrame.java:42）在com.example.requirements.RequirementsFrame.main（RequirementsFrame.java:182）引起：java.sql.SQLException：表/视图'APP.REQUIREMENTS'不存在。 at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException（未知来源） at org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA（Unknown Source） ......还有11个引起：ERROR 42X05：表/视图'APP.REQUIREMENTS'不存在。 at org.apache.derby.iapi.error.StandardException.newException（Unknown Source）在org.apache.derby.impl.sql.compile.FromBaseTable.bindTableDescriptor（未知来源） at org.apache.derby.impl.sql.compile.FromBaseTable.bindNonVTITables（未知来源）在org.apache.derby.impl.sql.compile.FromList.bindTables（未知来源）在org.apache.derby.impl.sql.compile.SelectNode.bindNonVTITables（未知来源） at org.apache.derby.impl.sql.compile.DMLStatementNode.bindTables（Unknown Source） at org.apache.derby.impl.sql.compile.DMLStatementNode.bind（Unknown Source） at org.apache.derby.impl.sql.compile.CursorNode.bindStatement（Unknown Source） at org.apache.derby.impl.sql.GenericStatement.prepMinion（Unknown Source）在org.apache.derby.impl.sql.GenericStatement.prepare（未知来源） at org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.prepareInternalStatement（Unknown Source） ......还有5个

任何想法是怎么回事？我的图书馆里有derby.jar。

Answer 1

您的代码显示“if！dbExists then createDatabase”。当你有一个新的空数据库时，dbExists可能会返回TRUE，因此你不会调用createDatabase，因此不会调用createTables。

Answer 2

您的数据库网址如何？它最后应该有一个“; create = true”......

BTW，考虑使用JPA而不是普通的JDBC

Answer 3

代码示例似乎并不完整，崩溃发生在getListEntries中，但从未在上面列出的代码中调用过。

Answer 4

你正在用catch块做一些非常糟糕的事情。您应该编辑每一个，以便它们都打印或记录堆栈跟踪。一个空的catch块意味着可以抛出异常，但你永远不会知道它。

为什么您认为需要在Java代码中创建表？对于大多数应用程序，架构由DBA设计和实现，因此在Java应用程序开始时它已经存在。为什么必须在运行时创建表？应该做一次。

德比表未被创建

4 个答案: