如果您的数据库不经常更改,您可以使用数据库的JDBC驱动程序附带的数据源,并在提供程序中隔离对第三方库的调用(我的示例使用H2数据库提供的调用,但所有JDBC提供程序都应该有一个).如果您更改为DataSource的不同实现(例如,C3PO、Apache DBCP或应用程序服务器容器提供的实现),则只需编写一个新的提供程序实现,即可从适当的位置获取数据源.在这里,我使用了单例作用域来允许DataSource实例在依赖它的类之间共享(池化是必需的).
public class DataSourceModule extends AbstractModule {
@Override
protected void configure() {
Names.bindProperties(binder(), loadProperties());
bind(DataSource.class).toProvider(H2DataSourceProvider.class).in(Scopes.SINGLETON);
bind(MyService.class);
}
static class H2DataSourceProvider implements Provider<DataSource> {
private final String url;
private final String username;
private final String password;
public H2DataSourceProvider(@Named("url") final String url,
@Named("username") final String username,
@Named("password") final String password) {
this.url = url;
this.username = username;
this.password = password;
}
@Override
public DataSource get() {
final JdbcDataSource dataSource = new JdbcDataSource();
dataSource.setURL(url);
dataSource.setUser(username);
dataSource.setPassword(password);
return dataSource;
}
}
static class MyService {
private final DataSource dataSource;
@Inject
public MyService(final DataSource dataSource) {
this.dataSource = dataSource;
}
public void singleUnitOfWork() {
Connection cn = null;
try {
cn = dataSource.getConnection();
// Use the connection
} finally {
try {
cn.close();
} catch (Exception e) {}
}
}
}
private Properties loadProperties() {
// Load properties from appropriate place...
// should contain definitions for:
// url=...
// username=...
// password=...
return new Properties();
}
}
要处理事务,应使用支持事务的数据源.我不建议手动实现此功能.但是,使用类似WARP-PERSISTEN或容器提供的事务管理,它将如下所示:
public class TxModule extends AbstractModule {
@Override
protected void configure() {
Names.bindProperties(binder(), loadProperties());
final TransactionManager tm = getTransactionManager();
bind(DataSource.class).annotatedWith(Real.class).toProvider(H2DataSourceProvider.class).in(Scopes.SINGLETON);
bind(DataSource.class).annotatedWith(TxAware.class).to(TxAwareDataSource.class).in(Scopes.SINGLETON);
bind(TransactionManager.class).toInstance(tm);
bindInterceptor(Matchers.any(), Matchers.annotatedWith(Transactional.class), new TxMethodInterceptor(tm));
bind(MyService.class);
}
private TransactionManager getTransactionManager() {
// Get the transaction manager
return null;
}
static class TxMethodInterceptor implements MethodInterceptor {
private final TransactionManager tm;
public TxMethodInterceptor(final TransactionManager tm) {
this.tm = tm;
}
@Override
public Object invoke(final MethodInvocation invocation) throws Throwable {
// Start tx if necessary
return invocation.proceed();
// Commit tx if started here.
}
}
static class TxAwareDataSource implements DataSource {
static ThreadLocal<Connection> txConnection = new ThreadLocal<Connection>();
private final DataSource ds;
private final TransactionManager tm;
@Inject
public TxAwareDataSource(@Real final DataSource ds, final TransactionManager tm) {
this.ds = ds;
this.tm = tm;
}
public Connection getConnection() throws SQLException {
try {
final Transaction transaction = tm.getTransaction();
if (transaction != null && transaction.getStatus() == Status.STATUS_ACTIVE) {
Connection cn = txConnection.get();
if (cn == null) {
cn = new TxAwareConnection(ds.getConnection());
txConnection.set(cn);
}
return cn;
} else {
return ds.getConnection();
}
} catch (final SystemException e) {
throw new SQLException(e);
}
}
// Omitted delegate methods.
}
static class TxAwareConnection implements Connection {
private final Connection cn;
public TxAwareConnection(final Connection cn) {
this.cn = cn;
}
public void close() throws SQLException {
try {
cn.close();
} finally {
TxAwareDataSource.txConnection.set(null);
}
}
// Omitted delegate methods.
}
static class MyService {
private final DataSource dataSource;
@Inject
public MyService(@TxAware final DataSource dataSource) {
this.dataSource = dataSource;
}
@Transactional
public void singleUnitOfWork() {
Connection cn = null;
try {
cn = dataSource.getConnection();
// Use the connection
} catch (final SQLException e) {
throw new RuntimeException(e);
} finally {
try {
cn.close();
} catch (final Exception e) {}
}
}
}
}