SQL查询在while循环中不起作用 - JAVA

Question

我在NetBeans上用Java编写了一个代码:

package helloworld;

import java.sql.*;
import java.io.*;
import java.lang.Object;
import java.io.IOException;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.*;
import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.collections.functors.EqualPredicate;
import org.apache.lucene.queryParser.ParseException;

public class HelloWorld {
    public static void main(String[] args) throws IOException, ParseException {
        // TODO code application logic here       
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

        String url = "jdbc:mysql://localhost:3306/kdd";
        String user = "root";
        String password = "Pass1234";    

        try {
            conn = DriverManager.getConnection(url, user, password);
            stmt = conn.createStatement();

            String sqlQuery = "Select * from ad_contents";
            rs = stmt.executeQuery(sqlQuery);

            while (rs.next()) { //(rs.next())              
                int adID = rs.getInt(1);
                String keywordTokens = rs.getString(2);
                String titleTokens = rs.getString(3);
                String descriptionTokens = rs.getString(4);

                List<String> keywordList = Arrays.asList(keywordTokens.split("\\|", -1));
                List<String> titleList = Arrays.asList(titleTokens.split("\\|", -1));
                List<String> descriptionList = Arrays.asList(descriptionTokens.split("\\|", -1));
                Set<String> distincts = new HashSet<String>();
                distincts.addAll(keywordList);
                distincts.addAll(titleList);
                distincts.addAll(descriptionList);

                int keywordHit = 0, titleHit = 0, descriptionHit = 0;

                for (String distinctCounter : distincts) {                    
                    keywordHit = CollectionUtils.cardinality(distinctCounter, keywordList);
                    titleHit = CollectionUtils.cardinality(distinctCounter, titleList);
                    descriptionHit = CollectionUtils.cardinality(distinctCounter, descriptionList);
                    String intoQuery = "insert into ad_word_counts values (" + adID + "," + distinctCounter + "," + keywordHit + "," + titleHit + "," + descriptionHit + ")";
                    stmt.execute(intoQuery);
                    //node myNode= new node(adID, Integer.parseInt(distinctCounter) , keywordHit, titleHit, descriptionHit);                                     
                }

            }           
        } catch (SQLException ex) {
        } finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (stmt != null) {
                    stmt.close();
                }
                if (conn != null) {
                    conn.close();
                }
            } catch (SQLException ex) {
            }
        }
    }
}

但是,对于rs Result Set的第一行,它只进入while块一次.因此,它仅为1个adID写入数据."intoQuery"不适用于所有rs Result Set行.我怎么处理它？

Answer 1

那是因为你在while循环中的for循环中再执行了一次查询: -

for (String distinctCounter : distincts) {                    

    // Create a new statement to execute query in while loop                
    Statement stmt1 = conn.createStatement();  
    stmt1.execute(intoQuery);

}

这将导致旧result set的关闭.

看看: - ResultSet#close文档,其中说: -

当Statement对象关闭,重新执行或用于从多个结果序列中检索下一个结果时,Statement对象会自动关闭它生成它的Statement对象.

因此,文档清楚地表明,使用相同的语句重新执行新查询将关闭该ResultSet对象.

因此,您需要使用其他statement实例来创建内部查询.

建议: -

理想情况下,您的上述代码会抛出一个SQLException(请参阅参考资料ResultSet#next),因为您在catch块中吞下了异常,因此您不必知道.

    catch (SQLException ex) {
    }

切勿使用empty挡块.它没用,除了它阻止你的程序在运行时停止.但它不会有任何好处.