Java Resultset.next（）while循环打印两次和

我正在尝试这个教程代码，它似乎从MySQL打印出了我的数据库两次。它来自下面的while循环：

 while (resultSet.next()) {
  // It is possible to get the columns via name
  // also possible to get the columns via the column number
  // which starts at 1
  // e.g. resultSet.getString(2);
  String user = resultSet.getString("myuser");
  String email = resultSet.getString("email");
  String website = resultSet.getString("webpage");
  String summary = resultSet.getString("summary");
  Date date = resultSet.getDate("datum");
  String comment = resultSet.getString("comments");
  System.out.println("User: " + user);
  System.out.println("Email: " + email);
  System.out.println("Website: " + website);
  System.out.println("Summary: " + summary);
  System.out.println("Date: " + date);
  System.out.println("Comment: " + comment);

}

那个循环打印两次。如果我在循环的末尾放一个break语句，它仍然会打印数据库的第一行两次。我认为这与resultSet.next（）有关。以下是完整的代码：

package de.vogella.mysql.first;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Date;

public class MySQLAccess {
private Connection connect = null;
private Statement statement = null;
private PreparedStatement preparedStatement = null;
private ResultSet resultSet = null;

public void readDataBase() throws Exception {
try {
  // This will load the MySQL driver, each DB has its own driver
  Class.forName("com.mysql.jdbc.Driver");
  // Setup the connection with the DB
  connect = DriverManager
      .getConnection("jdbc:mysql://localhost/feedback?"
          + "user=sqluser&password=sqluserpw");

  // Statements allow to issue SQL queries to the database
  statement = connect.createStatement();
  // Result set get the result of the SQL query
  resultSet = statement
      .executeQuery("select * from FEEDBACK.COMMENTS");
  writeResultSet(resultSet);

  // PreparedStatements can use variables and are more efficient
  preparedStatement = connect
      .prepareStatement("insert into  FEEDBACK.COMMENTS values (default, ?, ?, ?, ? , ?, ?)");
  // "myuser, webpage, datum, summary, COMMENTS from FEEDBACK.COMMENTS");
  // Parameters start with 1
  preparedStatement.setString(1, "Test");
  preparedStatement.setString(2, "TestEmail");
  preparedStatement.setString(3, "TestWebpage");
  preparedStatement.setDate(4, new java.sql.Date(2009-12-11));
  preparedStatement.setString(5, "TestSummary");
  preparedStatement.setString(6, "TestComment");
  preparedStatement.executeUpdate();

  preparedStatement = connect
      .prepareStatement("SELECT myuser, email, webpage, datum, summary, COMMENTS from FEEDBACK.COMMENTS");
  resultSet = preparedStatement.executeQuery();
  writeResultSet(resultSet);

  // Remove again the insert comment
  preparedStatement = connect
  .prepareStatement("delete from FEEDBACK.COMMENTS where myuser= ? ; ");
  preparedStatement.setString(1, "Test");
  preparedStatement.executeUpdate();

  resultSet = statement
  .executeQuery("select * from FEEDBACK.COMMENTS");
  writeMetaData(resultSet);

} catch (Exception e) {
  throw e;
} finally {
  close();
}

}

private void writeMetaData(ResultSet resultSet) throws SQLException {
//   Now get some metadata from the database
// Result set get the result of the SQL query

System.out.println("The columns in the table are: ");

System.out.println("Table: " + resultSet.getMetaData().getTableName(1));
for  (int i = 1; i<= resultSet.getMetaData().getColumnCount(); i++){
  System.out.println("Column " +i  + " "+ resultSet.getMetaData().getColumnName(i));
}
}

private void writeResultSet(ResultSet resultSet) throws SQLException {
// ResultSet is initially before the first data set
while (resultSet.next()) {
  // It is possible to get the columns via name
  // also possible to get the columns via the column number
  // which starts at 1
  // e.g. resultSet.getString(2);
  String user = resultSet.getString("myuser");
  String email = resultSet.getString("email");
  String website = resultSet.getString("webpage");
  String summary = resultSet.getString("summary");
  Date date = resultSet.getDate("datum");
  String comment = resultSet.getString("comments");
  System.out.println("User: " + user);
  System.out.println("Email: " + email);
  System.out.println("Website: " + website);
  System.out.println("Summary: " + summary);
  System.out.println("Date: " + date);
  System.out.println("Comment: " + comment);

 }
}

// You need to close the resultSet
private void close() {
try {
  if (resultSet != null) {
    resultSet.close();
  }

  if (statement != null) {
    statement.close();
  }

  if (connect != null) {
    connect.close();
  }
} catch (Exception e) {

}

package de.vogella.mysql.first；
导入java.sql.Connection；
导入java.sql.DriverManager；
导入java.sql.PreparedStatement；
导入java.sql.ResultSet；
导入java.sql.SQLException；
导入java.sql.Statement；
导入java.util.Date；
公共类MySQLAccess{
私有连接connect=null；
私有语句=null；
private PreparedStatement PreparedStatement=null；
私有ResultSet ResultSet=null；
public void readDataBase（）引发异常{
试一试{
//这将加载MySQL驱动程序，每个数据库都有自己的驱动程序
Class.forName（“com.mysql.jdbc.Driver”）；
//设置与数据库的连接
connect=DriverManager
.getConnection（“jdbc:mysql://localhost/feedback?"
+“user=sqluser&password=sqluserpw”）；
//语句允许向数据库发出SQL查询
语句=connect.createStatement（）；
//结果集获取SQL查询的结果
结果集=语句
.executeQuery（“从FEEDBACK.COMMENTS中选择*）；
writeResultSet（结果集）；
//PreparedStatements可以使用变量，效率更高
preparedStatement=connect
.prepareStatement（“插入到FEEDBACK.COMMENTS值中（默认值），，，，，，，，，，，）”；
//“我的用户、网页、数据、摘要、反馈意见。意见”）；
//参数以1开头
编制报表。设置字符串（1，“测试”）；
准备好的报表。设置字符串（2，“测试邮件”）；
准备好的声明。设置字符串（3，“测试网页”）；
setDate（4，新java.sql.Date（2009-12-11））；
编制报表。设置字符串（5，“测试摘要”）；
准备好的声明。集合字符串（6，“测试注释”）；
preparedStatement.executeUpdate（）；
preparedStatement=connect
.prepareStatement（“从反馈中选择myuser、电子邮件、网页、数据、摘要、评论”）；
resultSet=preparedStatement.executeQuery（）；
writeResultSet（结果集）；
//再次删除插入注释
preparedStatement=connect
.prepareStatement（“从FEEDBACK.COMMENTS中删除，其中myuser=？；”；
编制报表。设置字符串（1，“测试”）；
preparedStatement.executeUpdate（）；
结果集=语句
.executeQuery（“从FEEDBACK.COMMENTS中选择*）；
writeMetaData（结果集）；
}捕获（例外e）{
投掷e；
}最后{
close（）；
}
}
私有void writeMetaData（ResultSet ResultSet）引发SQLException{
//现在从数据库中获取一些元数据
//结果集获取SQL查询的结果
System.out.println（“表中的列为：”）；
System.out.println（“表：+resultSet.getMetaData（）.getTableName（1））；
对于（int i=1；i）您的代码调用writeResultSet（）两次：一次在插入之前，一次在插入之后。可能打印了两次，因为您调用了两次？查找writeResultSet调用。尝试注释第一个writeResultSet（）。然后执行。以连词结尾的标题？我肯定会看一看，但是