CSV导入导出

If there is a big data need to be export, don't use POI, or other tools. because it is slowly, Excel should be generator the font, background, border, merge cells, freezed cellls etc.  you should be know one thing, "the function more power, the system more complex, the speed more slowly.".
so use the easy api to export csv, then the user can translate the file to excel or other format , whatever.

package ycl.learn.excel.csv; 

/**
 Copyright 2005 Bytecode Pty Ltd.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */

import java.io.IOException;
import java.io.PrintWriter;
import java.io.Writer;
import java.util.Iterator;
import java.util.List;

/**
 * A very simple CSV writer released under a commercial-friendly license.
 *
 * @author Glen Smith
 *
 */
public class CSVWriter {
    
    private Writer rawWriter;

    private PrintWriter pw;

    private char separator;

    private char quotechar;
    
    private String lineEnd;

    /** The character used for escaping quotes. */
    public static final char ESCAPE_CHARACTER = '"';

    /** The default separator to use if none is supplied to the constructor. */
    public static final char DEFAULT_SEPARATOR = ',';

    /**
     * The default quote character to use if none is supplied to the
     * constructor.
     */
    public static final char DEFAULT_QUOTE_CHARACTER = '"';
    
    /** The quote constant to use when you wish to suppress all quoting. */
    public static final char NO_QUOTE_CHARACTER = '\u0000';
    
    /** Default line terminator uses platform encoding. */
    public static final String DEFAULT_LINE_END = "\n";

    /**
     * Constructs CSVWriter using a comma for the separator.
     *
     * @param writer
     *            the writer to an underlying CSV source.
     */
    public CSVWriter(Writer writer) {
        this(writer, DEFAULT_SEPARATOR);
    }

    /**
     * Constructs CSVWriter with supplied separator.
     *
     * @param writer
     *            the writer to an underlying CSV source.
     * @param separator
     *            the delimiter to use for separating entries.
     */
    public CSVWriter(Writer writer, char separator) {
        this(writer, separator, DEFAULT_QUOTE_CHARACTER);
    }

    /**
     * Constructs CSVWriter with supplied separator and quote char.
     *
     * @param writer
     *            the writer to an underlying CSV source.
     * @param separator
     *            the delimiter to use for separating entries
     * @param quotechar
     *            the character to use for quoted elements
     */
    public CSVWriter(Writer writer, char separator, char quotechar) {
    	this(writer, separator, quotechar, "\n");
    }

    /**
     * Constructs CSVWriter with supplied separator and quote char.
     *
     * @param writer
     *            the writer to an underlying CSV source.
     * @param separator
     *            the delimiter to use for separating entries
     * @param quotechar
     *            the character to use for quoted elements
     * @param lineEnd
     * 			  the line feed terminator to use
     */
    public CSVWriter(Writer writer, char separator, char quotechar, String lineEnd) {
        this.rawWriter = writer;
        this.pw = new PrintWriter(writer);
        this.separator = separator;
        this.quotechar = quotechar;
        this.lineEnd = lineEnd;
    }
    
    /**
     * Writes the entire list to a CSV file. The list is assumed to be a
     * String[]
     *
     * @param allLines
     *            a List of String[], with each String[] representing a line of
     *            the file.
     */
    public void writeAll(List allLines)  {

        for (Iterator iter = allLines.iterator(); iter.hasNext();) {
            String[] nextLine = (String[]) iter.next();
            writeNext(nextLine);
        }

    }
    
    /**
     * Writes the next line to the file.
     *
     * @param nextLine
     *            a string array with each comma-separated element as a separate
     *            entry.
     */
    public void writeNext(String[] nextLine) {
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < nextLine.length; i++) {

            if (i != 0) {
                sb.append(separator);
            }

            String nextElement = nextLine[i];
            if (nextElement == null)
                continue;
            if (quotechar !=  NO_QUOTE_CHARACTER)
            	sb.append(quotechar);
            for (int j = 0; j < nextElement.length(); j++) {
                char nextChar = nextElement.charAt(j);
                if (nextChar == quotechar) {
                    sb.append(ESCAPE_CHARACTER).append(nextChar);
                } else if (nextChar == ESCAPE_CHARACTER) {
                    sb.append(ESCAPE_CHARACTER).append(nextChar);
                } else {
                    sb.append(nextChar);
                }
            }
            if (quotechar != NO_QUOTE_CHARACTER)
            	sb.append(quotechar);
        }
        
        sb.append(lineEnd);
        pw.write(sb.toString());

    }

    /**
     * Close the underlying stream writer flushing any buffered content.
     *
     * @throws IOException if bad things happen
     *
     */
    public void close() throws IOException {
        pw.flush();
        pw.close();
        rawWriter.close();
    }

}

this method is copy from opencsv, not very complex, use reader, every time writer one line.

package ycl.learn.excel.csv; 

/**
 Copyright 2005 Bytecode Pty Ltd.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.util.ArrayList;
import java.util.List;

/**
 * A very simple CSV reader released under a commercial-friendly license.
 * 
 * @author Glen Smith
 * 
 */
public class CSVReader {

    private BufferedReader br;

    private boolean hasNext = true;

    private char separator;

    private char quotechar;
    
    private int skipLines;

    private boolean linesSkiped;

    /** The default separator to use if none is supplied to the constructor. */
    public static final char DEFAULT_SEPARATOR = ',';

    /**
     * The default quote character to use if none is supplied to the
     * constructor.
     */
    public static final char DEFAULT_QUOTE_CHARACTER = '"';
    
    /**
     * The default line to start reading.
     */
    public static final int DEFAULT_SKIP_LINES = 0;

    /**
     * Constructs CSVReader using a comma for the separator.
     * 
     * @param reader
     *            the reader to an underlying CSV source.
     */
    public CSVReader(Reader reader) {
        this(reader, DEFAULT_SEPARATOR);
    }

    /**
     * Constructs CSVReader with supplied separator.
     * 
     * @param reader
     *            the reader to an underlying CSV source.
     * @param separator
     *            the delimiter to use for separating entries.
     */
    public CSVReader(Reader reader, char separator) {
        this(reader, separator, DEFAULT_QUOTE_CHARACTER);
    }
    
    

    /**
     * Constructs CSVReader with supplied separator and quote char.
     * 
     * @param reader
     *            the reader to an underlying CSV source.
     * @param separator
     *            the delimiter to use for separating entries
     * @param quotechar
     *            the character to use for quoted elements
     */
    public CSVReader(Reader reader, char separator, char quotechar) {
        this(reader, separator, quotechar, DEFAULT_SKIP_LINES);
    }
    
    /**
     * Constructs CSVReader with supplied separator and quote char.
     * 
     * @param reader
     *            the reader to an underlying CSV source.
     * @param separator
     *            the delimiter to use for separating entries
     * @param quotechar
     *            the character to use for quoted elements
     * @param line
     *            the line number to skip for start reading 
     */
    public CSVReader(Reader reader, char separator, char quotechar, int line) {
        this.br = new BufferedReader(reader);
        this.separator = separator;
        this.quotechar = quotechar;
        this.skipLines = line;
    }

    /**
     * Reads the entire file into a List with each element being a String[] of
     * tokens.
     * 
     * @return a List of String[], with each String[] representing a line of the
     *         file.
     * 
     * @throws IOException
     *             if bad things happen during the read
     */
    public List readAll() throws IOException {

        List allElements = new ArrayList();
        while (hasNext) {
            String[] nextLineAsTokens = readNext();
            if (nextLineAsTokens != null)
                allElements.add(nextLineAsTokens);
        }
        return allElements;

    }

    /**
     * Reads the next line from the buffer and converts to a string array.
     * 
     * @return a string array with each comma-separated element as a separate
     *         entry.
     * 
     * @throws IOException
     *             if bad things happen during the read
     */
    public String[] readNext() throws IOException {

        String nextLine = getNextLine();
        return hasNext ? parseLine(nextLine) : null;
    }

    /**
     * Reads the next line from the file.
     * 
     * @return the next line from the file without trailing newline
     * @throws IOException
     *             if bad things happen during the read
     */
    private String getNextLine() throws IOException {
    	if (!this.linesSkiped) {
            for (int i = 0; i < skipLines; i++) {
                br.readLine();
            }
            this.linesSkiped = true;
        }
        String nextLine = br.readLine();
        if (nextLine == null) {
            hasNext = false;
        }
        return hasNext ? nextLine : null;
    }

    /**
     * Parses an incoming String and returns an array of elements.
     * 
     * @param nextLine
     *            the string to parse
     * @return the comma-tokenized list of elements, or null if nextLine is null
     * @throws IOException if bad things happen during the read
     */
    private String[] parseLine(String nextLine) throws IOException {

        if (nextLine == null) {
            return null;
        }

        List tokensOnThisLine = new ArrayList();
        StringBuffer sb = new StringBuffer();
        boolean inQuotes = false;
        do {
        	if (inQuotes) {
                // continuing a quoted section, reappend newline
                sb.append("\n");
                nextLine = getNextLine();
                if (nextLine == null)
                    break;
            }
            for (int i = 0; i < nextLine.length(); i++) {

                char c = nextLine.charAt(i);
                if (c == quotechar) {
                	// this gets complex... the quote may end a quoted block, or escape another quote.
                	// do a 1-char lookahead:
                	if( inQuotes  // we are in quotes, therefore there can be escaped quotes in here.
                	    && nextLine.length() > (i+1)  // there is indeed another character to check.
                	    && nextLine.charAt(i+1) == quotechar ){ // ..and that char. is a quote also.
                		// we have two quote chars in a row == one quote char, so consume them both and
                		// put one on the token. we do *not* exit the quoted text.
                		sb.append(nextLine.charAt(i+1));
                		i++;
                	}else{
                		inQuotes = !inQuotes;
                		// the tricky case of an embedded quote in the middle: a,bc"d"ef,g
                		if(i>2 //not on the begining of the line
                				&& nextLine.charAt(i-1) != this.separator //not at the begining of an escape sequence 
                				&& nextLine.length()>(i+1) &&
                				nextLine.charAt(i+1) != this.separator //not at the	end of an escape sequence
                		){
                			sb.append(c);
                		}
                	}
                } else if (c == separator && !inQuotes) {
                    tokensOnThisLine.add(sb.toString());
                    sb = new StringBuffer(); // start work on next token
                } else {
                    sb.append(c);
                }
            }
        } while (inQuotes);
        tokensOnThisLine.add(sb.toString());
        return (String[]) tokensOnThisLine.toArray(new String[0]);

    }

    /**
     * Closes the underlying reader.
     * 
     * @throws IOException if the close fails
     */
    public void close() throws IOException{
    	br.close();
    }
    
}

this is copy from opencsv, the reader speed is very well, will be reader one line at once.

so copy the test method.

package ycl.learn.excel.csv;

import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import ycl.learn.excel.ExcelHeader;
import ycl.learn.excel.ExcelHeader.ColumnHeader;

public class TestCSVWriter {
	
	private static final String DOWN_FILE = "C:\\Documents and Settings\\e557400\\workspace\\YclPlmTest\\DownUserHeader.csv";

	/**
	 * @param args
	 */
	public static void main(String[] args)throws Exception {
		// TODO Auto-generated method stub

		ColumnHeader[] chs = ExcelHeader.UserHeader.values();
		List<String[]> dataMapList = new ArrayList<String[]>();
		int j = 0;
		String[] dataMap = new String[chs.length];
		for(ColumnHeader ch:chs){
			dataMap[j] = ch.getName();
			j++;
		}
		dataMapList.add(dataMap);
		for(int i=0;i<10;i++){
			dataMap = new String[chs.length];
			j=0;
			for(ColumnHeader ch:chs){
				if(ch == ExcelHeader.UserHeader.ACTION){
					dataMap[j] = "i \"love\" you";
				}
				else if(ch == ExcelHeader.UserHeader.FIRST_NAME){
					dataMap[j] =  "2012-01-01";
				}
				else if(ch == ExcelHeader.UserHeader.LAST_NAME){
					dataMap[j] = "1.2365145";
				} 
				else if(ch == ExcelHeader.UserHeader.E_MAIL){
					dataMap[j] =  "aa";
				}
				else{
					dataMap[j] = "aanewnew2007";
				}
				j++;
			}
			dataMapList.add(dataMap);
		}
		Writer writer = new FileWriter(DOWN_FILE);
		CSVWriter csvWriter = new CSVWriter(writer); 
		csvWriter.writeAll(dataMapList);
		csvWriter.close();
		System.out.println("writer complete");
	}
	
}

after you generator the csv file, you can reader it.

package ycl.learn.excel.csv;

import java.io.FileReader;
import java.io.Reader;
import java.util.List;

public class TestCSVReader {

	private static final String DOWN_FILE = "C:\\Documents and Settings\\e557400\\workspace\\YclPlmTest\\DownUserHeader.csv";
	
	public static void main(String[] args)throws Exception {
		Reader reader = new FileReader(DOWN_FILE);
		CSVReader csvreader = new CSVReader(reader);
		List<String[]> list = csvreader.readAll();
		for(String[] line :list){
			for(String token:line){
				System.out.print(token+",");
			}
			System.out.println();
		}
	}
}

perfect, you export your data, and read your data, this is called persisdent to file system.