當從另一個csv文件開始創建csv文件時,我遇到了性能問題。 這是原始文件的外觀:在Java中創建大型csv文件變得非常慢
country,state,co,olt,olu,splitter,ont,cpe,cpe.latitude,cpe.longitude,cpe.customer_class,cpe.phone,cpe.ip,cpe.subscriber_id
COUNTRY-0001,STATE-0001,CO-0001,OLT-0001,OLU0001,SPLITTER-0001,ONT-0001,CPE-0001,28.21487,77.451775,ALL,SIP:[email protected],SIP:[email protected],CPE_SUBSCRIBER_ID-QHLHW4
COUNTRY-0001,STATE-0002,CO-0002,OLT-0002,OLU0002,SPLITTER-0002,ONT-0002,CPE-0002,28.294018,77.068924,ALL,SIP:[email protected],SIP:[email protected],CPE_SUBSCRIBER_ID-AH8NJQ
潛在它可能是數百萬這樣的線,我已經檢測到的問題1.280.000線。
這是算法:
File csvInputFile = new File(csv_path);
int blockSize = 409600;
brCsvInputFile = new BufferedReader(frCsvInputFile, blockSize);
String line = null;
StringBuilder sbIntermediate = new StringBuilder();
skipFirstLine(brCsvInputFile);
while ((line = brCsvInputFile.readLine()) != null) {
createIntermediateStringBuffer(sbIntermediate, line.split(REGEX_COMMA));
}
private static void skipFirstLine(BufferedReader br) throws IOException {
String line = br.readLine();
String[] splitLine = line.split(REGEX_COMMA);
LOGGER.debug("First line detected! ");
createIndex(splitLine);
createIntermediateIndex(splitLine);
}
private static void createIndex(String[] splitLine) {
LOGGER.debug("START method createIndex.");
for (int i = 0; i < splitLine.length; i++)
headerIndex.put(splitLine[i], i);
printMap(headerIndex);
LOGGER.debug("COMPLETED method createIndex.");
}
private static void createIntermediateIndex(String[] splitLine) {
LOGGER.debug("START method createIntermediateIndex.");
com.tekcomms.c2d.xml.model.v2.Metadata_element[] metadata_element = null;
String[] servicePath = newTopology.getElement().getEntity().getService_path().getLevel();
if (newTopology.getElement().getMetadata() != null)
metadata_element = newTopology.getElement().getMetadata().getMetadata_element();
LOGGER.debug(servicePath.toString());
LOGGER.debug(metadata_element.toString());
headerIntermediateIndex.clear();
int indexIntermediateId = 0;
for (int i = 0; i < servicePath.length; i++) {
String level = servicePath[i];
LOGGER.debug("level is: " + level);
headerIntermediateIndex.put(level, indexIntermediateId);
indexIntermediateId++;
// its identificator is going to be located to the next one
headerIntermediateIndex.put(level + "ID", indexIntermediateId);
indexIntermediateId++;
}
// adding cpe.latitude,cpe.longitude,cpe.customer_class, it could be
// better if it would be metadata as well.
String labelLatitude = newTopology.getElement().getEntity().getLatitude();
// indexIntermediateId++;
headerIntermediateIndex.put(labelLatitude, indexIntermediateId);
String labelLongitude = newTopology.getElement().getEntity().getLongitude();
indexIntermediateId++;
headerIntermediateIndex.put(labelLongitude, indexIntermediateId);
String labelCustomerClass = newTopology.getElement().getCustomer_class();
indexIntermediateId++;
headerIntermediateIndex.put(labelCustomerClass, indexIntermediateId);
// adding metadata
// cpe.phone,cpe.ip,cpe.subscriber_id,cpe.vendor,cpe.model,cpe.customer_status,cpe.contact_telephone,cpe.address,
// cpe.city,cpe.state,cpe.zip,cpe.bootfile,cpe.software_version,cpe.hardware_version
// now i need to iterate over each Metadata_element belonging to
// topology.element.metadata
// are there any metadata?
if (metadata_element != null && metadata_element.length != 0)
for (int j = 0; j < metadata_element.length; j++) {
String label = metadata_element[j].getLabel();
label = label.toLowerCase();
LOGGER.debug(" ==label: " + label + " index_pos: " + j);
indexIntermediateId++;
headerIntermediateIndex.put(label, indexIntermediateId);
}
printMap(headerIntermediateIndex);
LOGGER.debug("COMPLETED method createIntermediateIndex.");
}
讀取整個數據集,1.280.000線取800毫秒!所以這個問題是這種方法
private static void createIntermediateStringBuffer(StringBuilder sbIntermediate, String[] splitLine) throws ClassCastException,
NullPointerException {
LOGGER.debug("START method createIntermediateStringBuffer.");
long start, end;
start = System.currentTimeMillis();
ArrayList<String> hashes = new ArrayList<String>();
com.tekcomms.c2d.xml.model.v2.Metadata_element[] metadata_element = null;
String[] servicePath = newTopology.getElement().getEntity().getService_path().getLevel();
LOGGER.debug(servicePath.toString());
if (newTopology.getElement().getMetadata() != null) {
metadata_element = newTopology.getElement().getMetadata().getMetadata_element();
LOGGER.debug(metadata_element.toString());
}
for (int i = 0; i < servicePath.length; i++) {
String level = servicePath[i];
LOGGER.debug("level is: " + level);
if (splitLine.length > getPositionFromIndex(level)) {
String name = splitLine[getPositionFromIndex(level)];
sbIntermediate.append(name);
hashes.add(name);
sbIntermediate.append(REGEX_COMMA).append(HashUtils.calculateHash(hashes)).append(REGEX_COMMA);
LOGGER.debug(" ==sbIntermediate: " + sbIntermediate.toString());
}
}
// end=System.currentTimeMillis();
// LOGGER.info("COMPLETED adding name hash. " + (end - start) + " ms. " + (end - start)/1000 + " seg.");
// adding cpe.latitude,cpe.longitude,cpe.customer_class, it should be
// better if it would be metadata as well.
String labelLatitude = newTopology.getElement().getEntity().getLatitude();
if (splitLine.length > getPositionFromIndex(labelLatitude)) {
String lat = splitLine[getPositionFromIndex(labelLatitude)];
sbIntermediate.append(lat).append(REGEX_COMMA);
}
String labelLongitude = newTopology.getElement().getEntity().getLongitude();
if (splitLine.length > getPositionFromIndex(labelLongitude)) {
String lon = splitLine[getPositionFromIndex(labelLongitude)];
sbIntermediate.append(lon).append(REGEX_COMMA);
}
String labelCustomerClass = newTopology.getElement().getCustomer_class();
if (splitLine.length > getPositionFromIndex(labelCustomerClass)) {
String customerClass = splitLine[getPositionFromIndex(labelCustomerClass)];
sbIntermediate.append(customerClass).append(REGEX_COMMA);
}
// end=System.currentTimeMillis();
// LOGGER.info("COMPLETED adding lat,lon,customer. " + (end - start) + " ms. " + (end - start)/1000 + " seg.");
// watch out metadata are optional, it can appear as a void chain!
if (metadata_element != null && metadata_element.length != 0)
for (int j = 0; j < metadata_element.length; j++) {
String label = metadata_element[j].getLabel();
LOGGER.debug(" ==label: " + label + " index_pos: " + j);
if (splitLine.length > getPositionFromIndex(label)) {
String actualValue = splitLine[getPositionFromIndex(label)];
if (!"".equals(actualValue))
sbIntermediate.append(actualValue).append(REGEX_COMMA);
else
sbIntermediate.append("").append(REGEX_COMMA);
} else
sbIntermediate.append("").append(REGEX_COMMA);
LOGGER.debug(" ==sbIntermediate: " + sbIntermediate.toString());
}//for
sbIntermediate.append("\n");
end = System.currentTimeMillis();
LOGGER.info("COMPLETED method createIntermediateStringBuffer. " + (end - start) + " ms. ");
}
正如你所看到的,這種方法增加了一個預先計算的行到的StringBuffer,讀取輸入CSV文件中的每一行,從該行計算新的數據,最後生成的行添加到StringBuffer,所以最後我可以用這個緩衝區創建文件。
我已經運行jconsole,我可以看到沒有內存泄漏,我可以看到表示創建對象的鋸齒和gc回憶garbaje。它永遠不會拖垮內存堆棧閾值。
我注意到的一件事是,向StringBuffer添加新行所需的時間在幾ms範圍內完成(5,6,10),但隨着時間增加到(100-200 )毫秒和我懷疑在不久的將來,所以可能這是戰鬥馬。
我試圖對代碼進行分析,我知道有3圈,但他們都非常短褲,在只有8個元素的第一個循環迭代:
for (int i = 0; i < servicePath.length; i++) {
String level = servicePath[i];
LOGGER.debug("level is: " + level);
if (splitLine.length > getPositionFromIndex(level)) {
String name = splitLine[getPositionFromIndex(level)];
sbIntermediate.append(name);
hashes.add(name);
sbIntermediate.append(REGEX_COMMA).append(HashUtils.calculateHash(hashes)).append(REGEX_COMMA);
LOGGER.debug(" ==sbIntermediate: " + sbIntermediate.toString());
}
}
我已經meassured需要時間從分割線中獲得名稱,它毫無價值,0毫秒,與計算哈希方法相同,爲0毫秒。
其他循環實際上是相同的,迭代0到n,其中n是一個非常小的int,例如3到10,所以我不明白爲什麼它需要更多時間來完成該方法,唯一的我發現的事情是,添加一個新行到緩衝區正在變慢進程。
我正在考慮一個生產者消費者多線程策略,讀取每一行並將它們放入循環緩衝區的讀取器線程,另一個線程逐個處理它們,處理它們並將預先計算的行添加到StringBuffer中,是線程安全的,當文件完全獲得時,讀者線程發送消息給另一個線程,告訴他們停止。最後,我必須將此緩衝區保存到文件中。你怎麼看?這是一個好主意?
看到'newTopology.getElement()。getEntity()'和所有,你可能會使用臨時變量。並描述應用程序; NetBeans IDE可以開箱即用,但通常這應該值得研究。記錄中的一些toString調用可能代價很高。首先寫入文件可能會更好。至少根據文件大小提供初始容量,'new StringBuilder(100000);'。 – 2014-12-04 13:46:10
嗨Joop,謝謝你的迴應,newTopology.getElement()。getEntity()是一個屬性,從一個XML文件解析,它只計算一次。我將按照您對StringBuilder初始大小的建議。 – aironman 2014-12-04 14:06:27
無論何時需要擴展StringBuilder,Java都會創建一個新的char緩衝區,並將當前數據複製到新數組中,然後釋放舊數組。隨着StringBuilder變得越來越大,這個過程需要越來越多的時間。你爲什麼不直接把結果寫回文件? – markbernard 2014-12-04 14:15:15