[英]Reading CSV File Using Scanner Class Error
我有一個來自Java圖書示例的原始代碼。 該程序僅讀取一個文本文件(“ clients.txt”)。 但是,我想將“ clients.txt”修改為“ clients.csv”,並讓程序讀取“ .csv”文件。 我已經按照這種格式用“,”作為分隔符來解析數據,並且僅在下面的ReadTextFile.java
文件中添加/更新了兩行代碼:
添加/更新的代碼:
input = new Scanner( new File( "clients.csv" ) );
input.useDelimiter(",");
以為這是從讀取.txt
文件到.csv
文件的簡單修改,我收到了NoSuchElementException
或File improperly formed
.csv
File improperly formed
打印消息。
我知道還有其他一些類可以使用,例如BufferedReader
和/或CsvReader
類,但只是想弄清楚為什么input.useDelimiter()
方法在這里不起作用。
=====================
Process started >>>
<<< Process finished. (Exit code 0)
java ReadTextFileTest
Process started >>>
Account First Name Last Name Balance
File improperly formed.
<<< Process finished. (Exit code 1)
=====================
import java.io.File;
import java.io.FileNotFoundException;
import java.lang.IllegalStateException;
import java.util.NoSuchElementException;
import java.util.Scanner;
public class ReadTextFile
{
private Scanner input;
public void openFile()
{
try
{
// Orig code: input = new Scanner( new File( "clients.txt")
input = new Scanner( new File( "clients.csv")); // added/updated
input.useDelimiter(","); // added
}
catch ( FileNotFoundException fileNotFoundException )
{
System.err.println( "Error opening file." );
System.exit( 1 );
}
}
public void readRecords()
{
AccountRecord record = new AccountRecord();
System.out.printf( "%-10s%-12s%-12s%10s\n", "Account",
"First Name", "Last Name", "Balance" );
try
{
while ( input.hasNext() )
{
record.setAccount( input.nextInt() ); // read account number
record.setFirstName( input.next() ); // read first name
record.setLastName( input.next() ); // read last name
record.setBalance( input.nextDouble() ); // read balance
System.out.printf( "%-10d%-12s%-12s%10.2f\n",
record.getAccount(), record.getFirstName(),
record.getLastName(), record.getBalance() );
}
}
catch ( NoSuchElementException elementException )
{
System.err.println( "File improperly formed." );
input.close();
System.exit( 1 );
}
catch ( IllegalStateException stateException )
{
System.err.println( "Error reading from file." );
System.exit( 1 );
}
}
public void closeFile()
{
if ( input != null )
input.close();
}
}
=====================
public class ReadTextFileTest
{
public static void main( String args[] )
{
ReadTextFile application = new ReadTextFile();
application.openFile();
application.readRecords();
application.closeFile();
}
}
=====================
public class AccountRecord
{
private int account;
private String firstName;
private String lastName;
private double balance;
public AccountRecord()
{
this( 0, "", "", 0.0 );
}
public AccountRecord( int acct, String first, String last, double bal)
{
setAccount( acct );
setFirstName( first );
setLastName( last );
setBalance( bal );
}
public void setAccount( int acct ) { account = acct; } public int getAccount() { return account; }
public void setFirstName( String first )
{
firstName = first;
}
public String getFirstName()
{
return firstName;
}
public void setLastName( String last )
{
lastName = last;
}
public String getLastName()
{
return lastName;
}
public void setBalance( double bal )
{
balance = bal;
}
public double getBalance()
{
return balance;
}
}
==========================
100 Bob Jones 24.98
200 Steve Doe -345.67
300 Pam White 0.00
400 Sam Stone -42.16
500 Sue Rich 224.62
100 Bob Jones -4.98
200 Steve Doe 45.67
==============================================
100,Bob,Jones,24.98
200,Steve,Doe,-345.67
300,Pam,White,0.00
400,Sam,Stone,-42.16
500,Sue,Rich,224.62
100,Bob,Jones,-4.98
200,Steve,Doe,45.67
您的代碼嘗試讀取第一個余額時失敗。 由於您的定界符只是一個逗號( ,
)。 它嘗試將24.98<new-line>200
讀取為雙精度。
我們可以使用Pattern
將逗號和換行符用作分隔符。
import java.util.regex.Pattern;
Pattern delimiter = Pattern.compile(",|\\s");
input = new Scanner(new File("clients.csv")).useDelimiter(delimiter);
文件的一行上有一些尾隨空格,因此我使用了,|\\\\s
否則可以使用,|\\n
或,|\\n|\\r\\n
。
您的CSV文件必須為:
100,Bob,Jones,24.98,200,Steve,Doe,-345.67,300,Pam,White,0.00,400,Sam,Stone,-42.16,500,Sue,lastName,0.00
您的CSV文件不能包含\\n
(換行符),因為它將是程序的非法字符。 因為您的定界符是,
而不是\\n
。
但是,要保持您的clients.csv
文件不變,可以使用以下方法:
input.useDelimiter(Pattern.compile(",|\\n|\\r"));
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