ResultSet 关闭后不允许操作 (mysql, java)
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Operation not allowed after ResultSet closed (mysql, java)
提问by ratnesh
I was stuck with the error , here my line number 42 is while(rs.next()){, please help me with this i am stuck at this for few hrs.
我被错误困住了，这里我的第 42 行是while(rs.next()){，请帮我解决这个问题，我被困在这里几个小时。
> Exception in thread "main" java.sql.SQLException: Operation not allowed after ResultSet closed
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:998)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:937)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:872)
at com.mysql.jdbc.ResultSetImpl.checkClosed(ResultSetImpl.java:740)
at com.mysql.jdbc.ResultSetImpl.next(ResultSetImpl.java:6326)
at removeStopwords.RemoveStopwords.main(RemoveStopwords.java:42)
This is my code:
这是我的代码：
package removeStopwords;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.StringTokenizer;
import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;
public class RemoveStopwords {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost/mydbv2";
// Database credentials
static final String USER = "root";
static final String PASS = "***";
public static void main(String[] args) throws ClassNotFoundException, SQLException {
Connection conn = null;
Statement stmt = null;
Class.forName("com.mysql.jdbc.Driver");
conn = (Connection) DriverManager.getConnection(DB_URL, USER, PASS);
stmt = (Statement) conn.createStatement();
String sql;
ResultSet rs = null;
ResultSet rs2 = null;
ResultSet rs3 = null;
java.sql.PreparedStatement ps = null;
int event_id = 10;
sql = "SELECT id,text from tweet where event_id = " + event_id;
rs = stmt.executeQuery(sql);
String text = "";
Long id;
while (rs.next()) {
id = rs.getLong("id");
text = rs.getString("text");
System.out.println("tweet = " + text);
text = text.replaceAll("http[^\s]+", "");
text = text.replaceAll("www[^\s]+", "");
System.out.println("tweet after removal of links= " + text);
StringTokenizer st = new StringTokenizer(text);
while (st.hasMoreTokens()) {
String stopword = st.nextToken();
System.out.println("stopword : " + stopword);
sql = "SELECT * from stopwords WHERE word =" + '"'+stopword+'"';
rs2 = stmt.executeQuery(sql);
if (rs2.next()) {
text = text.replaceAll(stopword, "");
System.out.println("tweet after removing stopword = " + text);
}
sql = "SELECT * from filtertweet where tweet_id = " + id + "";
rs3 = stmt.executeQuery(sql);
if (!rs3.next()) {
sql = "INSERT INTO filtertweet VALUES(?,?)";
ps = conn.prepareStatement(sql);
ps.setLong(1, id);
ps.setString(2, text);
ps.executeUpdate();
}
}
}
stmt.close();
conn.close();
}
}
回答by Andreas
A Statementobject can have only one active ResultSet, so when you execute rs2 = stmt.executeQuery(sql), the first ResultSet (rs) gets closed.
一个Statement对象只能有一个 active ResultSet，因此当您执行时rs2 = stmt.executeQuery(sql)，第一个 ResultSet( rs) 将关闭。
Create two Statementobjects, one for rsand another for rs2.
创建两个Statement对象，一个用于rs，另一个用于rs2。
Quoting the javadoc of Statement:
引用 javadoc 的Statement：
By default, only one
ResultSetobject perStatementobject can be open at the same time. Therefore, if the reading of oneResultSetobject is interleaved with the reading of another, each must have been generated by differentStatementobjects. All execution methods in theStatementinterface implicitly close a statment's currentResultSetobject if an open one exists.
默认情况下，
ResultSet每个Statement对象只能同时打开一个对象。因此，如果一个ResultSet对象的读取与另一个对象的读取交织在一起，则每个Statement对象都必须由不同的对象生成。如果存在打开Statement的ResultSet对象，则接口中的所有执行方法都会隐式关闭语句的当前对象。
回答by Harish Sridharan
One ResultSet for one Statement is valid. When you are executing multiple queries use various Statements.
一个 Statement 的一个 ResultSet 是有效的。当您执行多个查询时，请使用各种语句。
public static void main(String[] args) throws ClassNotFoundException, SQLException {
Connection conn = null;
Statement stmt = null;
Class.forName("com.mysql.jdbc.Driver");
conn = (Connection) DriverManager.getConnection(DB_URL, USER, PASS);
stmt = (Statement) conn.createStatement();
String sql;
ResultSet rs = null;
ResultSet rs2 = null;
ResultSet rs3 = null;
java.sql.PreparedStatement ps = null;
int event_id = 10;
sql = "SELECT id,text from tweet where event_id = " + event_id;
rs = stmt.executeQuery(sql);
String text = "";
Long id;
while (rs.next()) {
id = rs.getLong("id");
text = rs.getString("text");
System.out.println("tweet = " + text);
text = text.replaceAll("http[^\s]+", "");
text = text.replaceAll("www[^\s]+", "");
System.out.println("tweet after removal of links= " + text);
StringTokenizer st = new StringTokenizer(text);
while (st.hasMoreTokens()) {
String stopword = st.nextToken();
System.out.println("stopword : " + stopword);
sql = "SELECT * from stopwords WHERE word =" + '"'+stopword+'"';
Statement stmt2 = conn.createStatement();
rs2 = stmt2.executeQuery(sql);
if (rs2.next()) {
text = text.replaceAll(stopword, "");
System.out.println("tweet after removing stopword = " + text);
}
sql = "SELECT * from filtertweet where tweet_id = " + id + "";
Statement stmt3 = conn.createStatement();
rs3 = stmt3.executeQuery(sql);
if (!rs3.next()) {
sql = "INSERT INTO filtertweet VALUES(?,?)";
ps = conn.prepareStatement(sql);
ps.setLong(1, id);
ps.setString(2, text);
ps.executeUpdate();
}
}
}
stmt.close();
conn.close();
}
