多线程从数据库中分页读,单线程将所有结果保存的数据库

本文介绍了一个使用多线程技术从数据库分页查询数据并导出到文件的应用案例。通过CyclicBarrier实现线程间的同步,确保所有查询线程完成后再统一将结果写入文件。

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public class OrderReadThread implements Runnable {

private List<Map<String, Object>> orderList;
private BaseDalClient dalClient;
private Map<String, Object> params;
private int totalRecords;
private CyclicBarrier cyclicBarrier;

@SuppressWarnings({ "rawtypes", "unchecked" })
@Override
public void run() {
// 每个线程分页查询,最终将结果放入公共的orderList
Page<?> pageInfo = dalClient.queryForListPage("eps.UserRegisterServiceImpl.selectOrderList", params,
totalRecords);
List tempList = pageInfo.getList();

orderList.addAll(tempList);
try {
// 子线程执行结束,等待其他未执行完的线程,如果所有线程都执行结束即执行同步线程
cyclicBarrier.await();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
}

public void setOrderList(List<Map<String, Object>> orderList) {
this.orderList = orderList;
}

public void setDalClient(BaseDalClient dalClient) {
this.dalClient = dalClient;
}

public void setParams(Map<String, Object> params) {
this.params = params;
}

public void setTotalRecords(int totalRecords) {
this.totalRecords = totalRecords;
}

public void setCyclicBarrier(CyclicBarrier cyclicBarrier) {
this.cyclicBarrier = cyclicBarrier;
}

}




public class FileWriteTaskThread implements Runnable {

private List<Map<String, Object>> orderList;

public FileWriteTaskThread(List<Map<String, Object>> orderList) {
this.orderList = orderList;
}

@Override
public void run() {
System.out.println("****************将所有子线程统计的最终的结果保存到文件中F*******************");

String outFileName = "order" + getCurrentTimeStr() + ".txt";
String outFilePath = "d:/order/" + outFileName;
BufferedWriter bw = null;
try {
bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(outFilePath), "UTF-8"));
for (Map<String, Object> order : orderList) {
StringBuilder line = new StringBuilder(200);

line.append(MapUtils.getString(order, "b2corderno", "")).append(",")
.append(MapUtils.getString(order, "phonenum", "")).append(",")
.append(MapUtils.getString(order, "customername", "")).append(",")
.append(MapUtils.getString(order, "customeraddress", "")).append(",")
.append(MapUtils.getString(order, "suppliercode", ""));

bw.write(line.toString());
bw.newLine();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (bw != null) {
IOUtils.closeQuietly(bw);
}
}

}

private String getCurrentTimeStr() {
Date d = new Date();
SimpleDateFormat format = new SimpleDateFormat("yyyyMMddHHmmss");
return format.format(d);
}

}




/**
* 每次查询1000条
*/
private static final int PERCENT_DOWNLOAD_NUM = 1000;

public static void main(String[] args) {
// 启动Spring容器
ApplicationContext context = new FileSystemXmlApplicationContext(
"file:src/main/webapp/WEB-INF/applicationContext.xml");
// 获取数据库操作类
BaseDalClient dalClient = context.getBean("dalClient", BaseDalClient.class);
// 查询总记录数
int totalRecords = dalClient
.queryForObject("eps.UserRegisterServiceImpl.selectOrderCount", null, Integer.class);

int temp = totalRecords / PERCENT_DOWNLOAD_NUM;
int queryCount = (totalRecords % PERCENT_DOWNLOAD_NUM) != 0 ? temp + 1 : temp;

List<Map<String, Object>> orderList = Collections.synchronizedList(new ArrayList<Map<String, Object>>());// 线程安全的List
// 同步辅助类,当所有子线程全部执行结束后来执行不同辅助类指定的同步线程FileWriteTaskThread
CyclicBarrier cyclicBarrier = new CyclicBarrier(queryCount, new FileWriteTaskThread(orderList));
for (int i = 1; i <= queryCount; i++) {
Map<String, Object> params = new HashMap<String, Object>();
params.put("pageSize", PERCENT_DOWNLOAD_NUM);
params.put("page", i);

OrderReadThread orderReadThread = new OrderReadThread();
orderReadThread.setDalClient(dalClient);
orderReadThread.setOrderList(orderList);
orderReadThread.setParams(params);
orderReadThread.setTotalRecords(totalRecords);
orderReadThread.setCyclicBarrier(cyclicBarrier);

// 启动多线程来从数据库中分页读取数据
Thread thread = new Thread(orderReadThread);
thread.start();
}
}
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