java 常見問題 之 不使用finally塊釋放資源

不使用finally塊釋放資源

錯誤的寫法：

public void save(File f) throws IOException {
OutputStream out = new BufferedOutputStream(new FileOutputStream(f));
out.write(...);
out.close();
}
public void load(File f) throws IOException {
InputStream in = new BufferedInputStream(new FileInputStream(f));
in.read(...);
in.close();
}

數據庫訪問也涉及到類似的情況：

Car getCar(DataSource ds, String plate) throws SQLException {
 Car car = null;
 Connection c = null;
 PreparedStatement s = null;
 ResultSet rs = null;
try {
 c = ds.getConnection();
 s = c.prepareStatement("select make, color from cars where plate=?");
 s.setString(1, plate);
 rs = s.executeQuery();
 if (rs.next()) {
 car = new Car();
 car.make = rs.getString(1);
 car.color = rs.getString(2);
}
} finally {
 if (rs != null) try { rs.close(); } catch (SQLException e) { }
 if (s != null) try { s.close(); } catch (SQLException e) { }
 if (c != null) try { c.close(); } catch (SQLException e) { }
}
 return car;
}

數據庫訪問也涉及到類似的情況：

Car getCar(DataSource ds, String plate) throws SQLException {
 Car car = null;
 Connection c = null;
 PreparedStatement s = null;
 ResultSet rs = null;
try {
 c = ds.getConnection();
 s = c.prepareStatement("select make, color from cars where plate=?");
 s.setString(1, plate);
 rs = s.executeQuery();
 if (rs.next()) {
 car = new Car();
 car.make = rs.getString(1);
 car.color = rs.getString(2);
}
} finally {
 if (rs != null) try { rs.close(); } catch (SQLException e) { }
 if (s != null) try { s.close(); } catch (SQLException e) { }
 if (c != null) try { c.close(); } catch (SQLException e) { }
}
 return car;
}