Question

请教一个java问题，结果集已关闭？ 部分代码如下，请大神帮助？

public ResultSet Query(String sqlStr)
{ Connection conn=null;
Statement st=null;
ResultSet rs=null;
try{
conn=this.getConnection();
st=conn.createStatement();
System.out.println("SQL:"+sqlStr);
rs=st.executeQuery(sqlStr);
if(rs!=null){
rs.close();
}
if(st!=null){
st.close();
}
if(conn!=null){
conn.close();
}
}
catch(Exception e)
{
e.printStackTrace();
}
return rs;
}

‘’''
public static void main(String args[]) throws Exception
{
DB db=new DB();
String Str="select * from users";
ResultSet rs=db.Query(Str);
if(rs.next())
{
System.out.println(rs.getString("uname"));
}
}

Answer 1

方法调用结束，你的结果集已经关闭了，肯定无法获取到结果集了
ResultSet 结果集对象最好不要作为参数传来传去，可以使用一个实体进行传值
比如 User ( username, password )
public class User {
private String username;
private String password;
public String getUsername() {
return username == null ? "" : username.trim();
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password == null ? "" : password.trim();
}
public void setPassword(String password) {
this.password = password;
}
}

public List<User> Query(String sqlStr) {
List<User> users = new ArrayList<User>();

Connection conn = null;
Statement st = null;
ResultSet rs = null;
try {
conn = this.getConnection();
st = conn.createStatement();
rs = st.executeQuery(sqlStr);
while(rs.next()){
User user = new User();
user.setUsername(rs.getString("username"));
user.setPassword(rs.getString("password"));
users.add(user);
}
} catch (Exception e) {
e.printStackTrace();
} finally{
try{
if (rs != null) {
rs.close();
}
if (st != null) {
st.close();
}
if (conn != null) {
conn.close();
}
} catch(Exception e) {
e.printStackTrace();
}
}
return users;
}

public static void main(String args[]) throws Exception {
DB db = new DB();
String Str = "select * from users";
List<User> users = db.Query(Str);
for (int i = 0; i < users.size(); i++) {
System.out.println(users.get(i).getUsername());
}
}

Answer 2

在Query方法里
if(rs!=null){
rs.close();
}
如果结果集不为null，你进行了关闭，所以在main方法里调用if(rs.next())时候会报错，其实需要关闭时候，你可以在catch后边加finally，在里边进行判断和关闭

Answer 3

在你的代码第11行中：
if(rs!=null){
rs.close();
}
你是不是判断错了？是如果为空关闭。
当前查到的rs是不为空的，还没执行到下边你就把他关闭了

Answer 4

package org.demo.base;
import java.sql.*;import java.util.*;
public class Conn {

public static Connection createConn() {
数据库连接
}

public static void close(Connection conn) {
if (conn == null)
return;
try {
conn.close();
conn = null;
} catch (SQLException e) {
e.printStackTrace();
}
}

public static void close(Statement stat) {
if (stat == null)
return;
try {
stat.close();
stat = null;
} catch (SQLException e) {
e.printStackTrace();
}
}

public static void close(ResultSet rs) {
if (rs == null)
return;
try {
rs.close();
rs = null;
} catch (SQLException e) {
e.printStackTrace();
}
}

public ResultSet getTaskthreeList(String sql) {
try {
Connection conn= createConn();
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(sql);

close(rs);
close(stmt);
close(conn);
} catch (SQLException e) {
e.printStackTrace();
}
return rs;
}

}

Answer 5

return rs;往前提到rs=st.executeQuery(sqlStr);后 增加finally 在finally块中关闭连接 适配器 和 结果集