大家好，又见面了，我是你们的朋友全栈君。
Derby並不是一個新的數據庫產品,它是由IBM捐獻給Apache的DB項目的一個純Java數據庫,JDK6.0里面帶的這個Derby的版本是10.2.1.7,支持存儲過程和觸發器;有兩種運行模式,一種是作為嵌入式數據庫,另一種是作為網絡數據庫,前者的數據庫服務器和客戶端都在同一個JVM里面運行,后者允許數據庫服務器端和客戶端不在同一個JVM里面,而且允許這兩者在不同的物理機器上.值得注意的是JDK6里面的這個Derby支持JDK6的新特性JDBC 4.0規范(JSR 221),現在我們如果要練習JDBC的用法,沒有必要單獨裝一個數據庫產品了,直接用Derby就行.
下面是個使用derby的簡單例子:
首先導入JAR包:derby.jar,如果你裝的是JDK6,在C:/Program Files/Sun/JavaDB/lib目錄下就可以找到.
然后就要創建數據庫了:
Java代碼 
privateConnection getConnection()throwsSQLException {
Connection connection = DriverManager
.getConnection(“jdbc:derby:userDB;create=true;user=test;password=test”);
connection.setAutoCommit(false);
returnconnection;
}private Connection getConnection() throws SQLException {
Connection connection = DriverManager
.getConnection(“jdbc:derby:userDB;create=true;user=test;password=test”);
connection.setAutoCommit(false);
return connection;
}
其中userDB是要連接數據庫的名字,create=true表示如果該數據庫不存在,則創建該數據庫,如果數據庫存在,則用用戶user=test;密碼password=test連接數據庫.
有了數據庫,接下來該建表了:
Java代碼
privatevoidcreateTable(Connection connection)throwsSQLException {
Statement statement = connection.createStatement();
String sql =”create table USERS(“
+” ID BIGINT not null generated by default as identity,”
+” USER_NAME VARCHAR(20) not null,”
+” PASSWORD VARCHAR(20),”
+” constraint P_KEY_1 primary key (ID))”;
statement.execute(sql);
sql =”create unique index USER_NAME_INDEX on USERS (“
+” USER_NAME ASC)”;
statement.execute(sql);
statement.close();
}private void createTable(Connection connection) throws SQLException {
Statement statement = connection.createStatement();
String sql = “create table USERS(“
+ ” ID BIGINT not null generated by default as identity,”
+ ” USER_NAME VARCHAR(20) not null,”
+ ” PASSWORD VARCHAR(20),”
+ ” constraint P_KEY_1 primary key (ID))”;
statement.execute(sql);
sql = “create unique index USER_NAME_INDEX on USERS (“
+ ” USER_NAME ASC)”;
statement.execute(sql);
statement.close();
}
創建了USERS表,包括ID,USER_NAME,PASSWORD三個列,其中ID是主鍵,其中generated by default as identity的作用類似sequence,identity是定義自動加一的列,
GENERATED BY ALWAYS AS IDENTITY
GENERATED BY DEFAULT AS IDENTITY
By always和by default是說明生成這個IDENTITY的方式。
By always是完全由系統自動生成。
by default是可以由用戶來指定一個值。
編寫與USERS表對應的javabean(這個就不多說了),:
Java代碼
publicclassUserimplementsSerializable {
/**
*
*/
privatestaticfinallongserialVersionUID = 1L;
privateLong id;
privateString userName;
privateString password;
publicLong getId() {
returnid;
}
publicvoidsetId(Long id) {
this.id = id;
}
publicString getUserName() {
returnuserName;
}
publicvoidsetUserName(String userName) {
this.userName = userName;
}
publicString getPassword() {
returnpassword;
}
publicvoidsetPassword(String password) {
this.password = password;
}
}public class User implements Serializable {
/**
*
*/
private static final long serialVersionUID = 1L;
private Long id;
private String userName;
private String password;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
接下來就可以就數據庫進行增刪改查的操作了:
插入數據:
Java代碼
privatevoidcreate(User user) {
Connection connection =null;
try{
connection =this.getConnection();
PreparedStatement statement = connection
.prepareStatement(“insert into users (user_name,password) values(?,?)”);
intindex =1;
statement.setString(index++, user.getUserName());
statement.setString(index++, user.getPassword());
statement.execute();
user.setId(this.getId(connection));
connection.commit();
}catch(SQLException e) {
rollback(connection);
thrownewRuntimeException(e);
}finally{
if(connection !=null) {
close(connection);
}
}
}private void create(User user) {
Connection connection = null;
try {
connection = this.getConnection();
PreparedStatement statement = connection
.prepareStatement(“insert into users (user_name,password) values(?,?)”);
int index = 1;
statement.setString(index++, user.getUserName());
statement.setString(index++, user.getPassword());
statement.execute();
user.setId(this.getId(connection));
connection.commit();
} catch (SQLException e) {
rollback(connection);
throw new RuntimeException(e);
} finally {
if (connection != null) {
close(connection);
}
}
}
Java代碼
privateLong getId(Connection connection)throwsSQLException {
CallableStatement callableStatement = connection
.prepareCall(“values identity_val_local()”);
ResultSet resultSet = callableStatement.executeQuery();
resultSet.next();
Long id = resultSet.getLong(1);
resultSet.close();
callableStatement.close();
returnid;
}private Long getId(Connection connection) throws SQLException {
CallableStatement callableStatement = connection
.prepareCall(“values identity_val_local()”);
ResultSet resultSet = callableStatement.executeQuery();
resultSet.next();
Long id = resultSet.getLong(1);
resultSet.close();
callableStatement.close();
return id;
}
getId方法是獲得系統默認的id值,是通過identity_val_local()獲得的,而函數IDENTITY_VAL_LOCAL()則可以在INSERT語句執行之后，為我們返回剛才系統為id所產生的值.感覺還是有點想sequence的curr_val.
修改數據:
Java代碼
privatevoidupdate(User user) {
Connection connection =null;
try{
connection =this.getConnection();
PreparedStatement statement = connection
.prepareStatement(“update users set user_name=?,password=? where id=?”);
intindex =1;
statement.setString(index++, user.getUserName());
statement.setString(index++, user.getPassword());
statement.setLong(index++, user.getId());
statement.execute();
connection.commit();
}catch(SQLException e) {
rollback(connection);
thrownewRuntimeException(e);
}finally{
if(connection !=null) {
close(connection);
}
}
}private void update(User user) {
Connection connection = null;
try {
connection = this.getConnection();
PreparedStatement statement = connection
.prepareStatement(“update users set user_name=?,password=? where id=?”);
int index = 1;
statement.setString(index++, user.getUserName());
statement.setString(index++, user.getPassword());
statement.setLong(index++, user.getId());
statement.execute();
connection.commit();
} catch (SQLException e) {
rollback(connection);
throw new RuntimeException(e);
} finally {
if (connection != null) {
close(connection);
}
}
}
刪除數據:
Java代碼
publicvoiddelete(Long id) {
Connection connection =null;
try{
connection =this.getConnection();
PreparedStatement statement = connection
.prepareStatement(“delete from users where id=?”);
statement.setLong(1, id);
statement.execute();
connection.commit();
}catch(SQLException e) {
rollback(connection);
thrownewRuntimeException(e);
}finally{
if(connection !=null) {
close(connection);
}
}
}public void delete(Long id) {
Connection connection = null;
try {
connection = this.getConnection();
PreparedStatement statement = connection
.prepareStatement(“delete from users where id=?”);
statement.setLong(1, id);
statement.execute();
connection.commit();
} catch (SQLException e) {
rollback(connection);
throw new RuntimeException(e);
} finally {
if (connection != null) {
close(connection);
}
}
}
查詢數據:
Java代碼
publicUser findById(Long id) {
Connection connection =null;
try{
connection =this.getConnection();
PreparedStatement statement = connection
.prepareStatement(“select user_name,password from users where id=?”);
statement.setLong(1, id);
ResultSet resultSet = statement.executeQuery();
User user =null;
if(resultSet.next()) {
user =newUser();
user.setId(id);
user.setUserName(resultSet.getString(“user_name”));
user.setPassword(resultSet.getString(“password”));
}
resultSet.close();
statement.close();
connection.commit();
returnuser;
}catch(SQLException e) {
thrownewRuntimeException(e);
}finally{
if(connection !=null) {
close(connection);
}
}
}public User findById(Long id) {
Connection connection = null;
try {
connection = this.getConnection();
PreparedStatement statement = connection
.prepareStatement(“select user_name,password from users where id=?”);
statement.setLong(1, id);
ResultSet resultSet = statement.executeQuery();
User user = null;
if (resultSet.next()) {
user = new User();
user.setId(id);
user.setUserName(resultSet.getString(“user_name”));
user.setPassword(resultSet.getString(“password”));
}
resultSet.close();
statement.close();
connection.commit();
return user;
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
if (connection != null) {
close(connection);
}
}
}
以上就是derby的簡單操作.
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