我正在使用jersey創建簡單的rest api，在這里我將從數據庫中獲取的所有數據分配給變量，然后將這些變量數據作為列表返回，但出現錯誤。我看過其他示例，但我不明白這是怎么回事，這是我所做的：public class UserDAOImpl implements UserDAO{public List<User> readUser() { List<User> list = new ArrayList(); User u = new User(); try { System.out.println("inside readuser impl"); Class.forName("com.mysql.jdbc.Driver"); Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/userdb", "root", ""); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery("select * from user"); while (rs.next()) { int id = rs.getInt("id"); String name = rs.getString("name"); String address = rs.getString("address"); u.setId(id); u.setName(name); u.setAddress(address); System.out.println(u); list.add(u); //adding user object to list con.close(); } } catch (Exception e) { System.out.println(e); } return list; //returning to list for json response }}這是我的控制器，在獲取對象后給出json響應@Path("/rest")public class UserController {@GET@Path("/getall")@Produces(MediaType.APPLICATION_JSON)public List<User> getAllUser(){ UserDAO udao = new UserDAOImpl(); return udao.readUser(); }}
1 回答
蠱毒傳說
TA貢獻1895條經驗 獲得超3個贊
您將在一次迭代后關閉連接，這將導致在第二次迭代時在javasql異常上關閉ResultSet后不允許操作，將con.close移到循環外
public class UserDAOImpl implements UserDAO{
public List<User> readUser() {
List<User> list = new ArrayList();
User u = new User();
try {
System.out.println("inside readuser impl");
Class.forName("com.mysql.jdbc.Driver");
Connection con =
DriverManager.getConnection("jdbc:mysql://localhost:3306/userdb", "root", "");
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("select * from user");
while (rs.next()) {
int id = rs.getInt("id");
String name = rs.getString("name");
String address = rs.getString("address");
u.setId(id);
u.setName(name);
u.setAddress(address);
System.out.println(u);
list.add(u); //adding user object to list
}
} catch (Exception e) {
System.out.println(e);
}
con.close();
return list; //returning to list for json response
}
}
甚至您可以對資源使用try它將自動關閉所有資源
public class UserDAOImpl implements UserDAO{
public List<User> readUser() {
List<User> list = new ArrayList();
User u = new User();
try( Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/userdb", "root", "");
Statement stmt = con.createStatement();ResultSet rs = stmt.executeQuery("select * from user");){
System.out.println("inside readuser impl");
while (rs.next()) {
int id = rs.getInt("id");
String name = rs.getString("name");
String address = rs.getString("address");
u.setId(id);
u.setName(name);
u.setAddress(address);
System.out.println(u);
list.add(u); //adding user object to list
}
} catch (Exception e) {
System.out.println(e);
}
return list; //returning to list for json response
}
}
我沒有測試第二個，因為我沒有這臺機器的環境
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