mysql 分页分批导出_将分批分页查询的数据导出成excel表格
将分批分页查询的数据导出成excel表格
将数据库中的数据按照一定的过滤和排序规则，进行分批分页查询后生成Excel或者其他形式的报表数据，然后提供前端给下载是一个比较常见的业务场景，而且一般还会限定最大的行数，或者由前端指定行数。其实这个逻辑比较简单，分批查询数据，用几个for循环就可以搞定。但是报表很多的话，写起来也有点烦。于是想到把分页数据包装成流，简化api。 定义了几个简单的类，只要查询数据的Service层方法实现PagingQuery接口，而Domain实现CsvLine接口即可。
CsvLine.java
/**
* @author zouk
**/
public interface CsvLine {
/**
* generate a line
*
* @return a csv line
*/
String[] csvLine();
}
PagingQuery.java
import java.util.List;
/**
* @author zouk
**/
public interface PagingQuery {
/**
* paging query data base
*
* @param offset offer for sql
* @param limit limit for sql
* @return list of CsvLine
*/
List query(int offset, int limit);
}
CsvLineStreamBuilder.java
import java.util.Iterator;
import java.util.function.Supplier;
import java.util.stream.Stream;
/**
* @author zouk
**/
public class CsvLineStreamBuilder {
@SuppressWarnings("unchecked")
public static Stream create(final PagingQuery pagingQuery, final int limit, final int queryPageSize) {
Supplier supplier = new Supplier() {
Iterator iterator = pagingQuery.query(0, queryPageSize).iterator();
String[] nextLine;
int count = 0;
boolean noMore = false;
@Override
public String[] get() {
if (count > limit || noMore) {
return new String[]{};
}
if (iterator.hasNext()) {
nextLine = iterator.next().csvLine();
} else {
iterator = pagingQuery.query(count, queryPageSize).iterator();
if (iterator.hasNext()) {
nextLine = iterator.next().csvLine();
} else {
noMore = true;
--count;
nextLine = new String[]{};
}
}
++count;
return nextLine;
}
};
return Stream.generate(supplier).limit(limit);
}
}
ExcelWriter.java
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.function.Consumer;
import java.util.stream.Stream;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.xssf.streaming.SXSSFWorkbook;
/**
* @author zouk
**/
public class ExcelWriter {
private static final int ROW_WINDOW_SIZE = 100;
public static void streamToExcel(Stream stream, String[] fieldNames, String excelFile) throws IOException {
SXSSFWorkbook wb = new SXSSFWorkbook(ROW_WINDOW_SIZE);
Sheet sh = wb.createSheet();
Row firstRow = sh.createRow(0);
for (int colNum = 0; colNum < fieldNames.length; ++colNum) {
Cell cell = firstRow.createCell(colNum);
cell.setCellValue(fieldNames[colNum]);
}
stream.forEachOrdered(new Consumer() {
int rowNum = 1;
@Override
public void accept(String[] csvLine) {
Row row = sh.createRow(rowNum);
for (int colNum = 0; colNum < csvLine.length; ++colNum) {
Cell cell = row.createCell(colNum);
cell.setCellValue(csvLine[colNum]);
}
++rowNum;
}
});
FileOutputStream fOut = new FileOutputStream(excelFile);
wb.write(fOut);
fOut.close();
wb.dispose();
}
}