public class BaseDao {
protected Connection conn=null;
protected PreparedStatement ps=null;
protected Statement stmt=null;
protected ResultSet rs=null;
public boolean getConnection(){
//读出配置信息
String driver=ConfigManager.getInstance().getString("jdbc.driver_class");
String url=ConfigManager.getInstance().getString("jdbc.connection.url");
String username=ConfigManager.getInstance().getString("jdbc.connection.username");
String password=ConfigManager.getInstance().getString("jdbc.connection.password");
//加载JDBC驱动
try { Class.forName(driver);
//与数据库建立连接
conn=DriverManager.getConnection(url, username, password);
} catch (ClassNotFoundException e) {
e.printStackTrace();
return false;
} catch (SQLException e) {
e.printStackTrace();
return false;
}
return true;
}
//增删改操作
public int executeUpdate(String sql,Object[] params){
int updateRows=0;
getConnection();
try {
ps=conn.prepareStatement(sql);
//填充占位符
for(int i=0;i<params.length;i++){
ps.setObject(i+1, params[i]);
}
//System.out.println(sql);
updateRows=ps.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}finally{
closeResource();
}
return updateRows;
}
//查询操作
public ResultSet executeSQL(String sql,Object[] params){
getConnection();
try {
ps=conn.prepareStatement(sql);
//填充占位符
for(int i=0;i<params.length;i++){
ps.setObject(i++, params[i]);
}
rs=ps.executeQuery();
} catch (SQLException e) {
e.printStackTrace();
}finally{
closeResource();
}
return rs;
}
//关闭资源
public boolean closeResource(){
if(rs!=null){
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
return false;
}
}
if(ps!=null){
try {
ps.close();
} catch (SQLException e) {
e.printStackTrace();
return false;
}
}
if(conn!=null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
return false;
}
}
return true;
}
}
Here is what I wrote a class that implements the interface
public class BookDaoImpl extends BaseDao implements BookDao {
//获取图书列表
@Override
public List<Book> getBookList() {
List<Book> bookList=new ArrayList<Book>();
try {
//获得Statement对象，执行SQL语句
String sql="select * from books";
Object[] params={};
ResultSet rs=this.executeSQL(sql, params);
//处理执行结果（ResultSet）
while(rs.next()){
System.out.println("运行到这了吗");
int bid =rs.getInt("bid");
String bookname=rs.getString("bookname");
String b_price=rs.getString("b_price");
String image=rs.getString("image");
int stock=rs.getInt("stock");
//将图书信息封装成对象
Book book=new Book();
book.setBid(bid);
book.setBookName(bookname);
book.setPrice(b_price);
book.setImage(image);
book.setStock(stock);
//将图书对象放进集合中
bookList.add(book);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
this.closeResource();
}
return bookList;
}
}
Here is a test of my class when I run this class is always reported the following exception
public static void main(String[] args) {
BookDaoImpl bookDao=new BookDaoImpl();
List<Book> bookList=bookDao.getBookList();
for(Book book:bookList){
System.out.println(book.getBid()+"\t"+book.getBookName()+"\t"+book.getPrice()+"\t"+book.getStock());
}
anomaly investigation said a lot of information is multi-threaded concurrency issues , but I just do not know where it appeared , seeking Great God help ah !
java.sql.SQLException: 关闭的 Resultset: next
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:146)
at oracle.jdbc.driver.OracleResultSetImpl.next(OracleResultSetImpl.java:175)
at com.bdqn.OA.Dao.Impl.BookDaoImpl.getBookList(BookDaoImpl.java:37)
at com.bdqn.OA.Dao.Impl.BookDaoImpl.main(BookDaoImpl.java:223)
------ Solution ------------------------------------ --------
your BookDaoImpl how to inherit a BookDao and achieve a BookDao?
ResultSet rs = this.executeSQL (sql, params);
executeSQL way you have to call the parent class closeResource (); method
that is, you call rs.next () before , has closed ResultSet!
so we wrong !
------ Solution ---------------------------------------- ----
executeSQL calls to close the ResultSet
------ Solution --------------------------- -----------------
Yes, you BaseDao in the parent class method in a query executeSQL not directly close closeResource (); is not the first to write finally, since the use resultset he was disconnected once and databases , data sets where the data is also gone, but there are finally in the subclass method, so the parent class can save
------ Solution ----- ---------------------------------------
floor to explain it place
------ For reference only ------------------------------------- -
your BookDaoImpl how to inherit a BookDao and achieve a BookDao?
ResultSet rs = this.executeSQL (sql, params);
executeSQL way you have to call the parent class closeResource (); method
that is, you call rs.next () before , has closed ResultSet!
so we wrong !
I inherited one of BookDaoImpl BaseDao and implement a BookDao
I now find the cause of the error , that is because I executeSQL BaseDao tool class and the executeUpdate method in the finally executed closeResource closed Rideau resource methods, making ResultSet was closed, very grateful to the four upstairs correction !
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