我有一个经过哈希映射的csv文件,每当用户输入城市名称(键(时,它都会显示该城市的所有详细信息。我必须优化搜索结果时间,每次它读取文件(而不是只有一次(并显示值。CSV文件包含如下数据:
城市,city_ascii,纬度,液化天然气,国家,ISO2,ISO3,admin_name,首都,人口,ID Malishevë,Malisheve,42.4822,20.7458,科索沃,XK,XKS,Malishevë,admin,,1901597212 普里兹伦,普里兹伦,42.2139,20.7397,科索沃,XK,XKS,普里兹伦,admin,,1901360309 祖宾波托克,祖宾波托克,42.9144,20.6897,科索沃,XK,XKS,祖宾 波托克,管理员,1901608808
import java.io.File;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Scanner;
import java.io.IOException;
public class CSVFileReaders{
public static void main(String[] args) {
String filePath = "C:\worldcities1.csv";
Scanner in = new Scanner(System.in);
System.out.println(" n Enter the City name to be Searched : n _> ");
long start = System.currentTimeMillis();
String searchTerm = in.nextLine();
readAndFindRecordFromCSV(filePath, searchTerm);
long end = System.currentTimeMillis();
System.out.println(" n It took " + (end - start) + " Milli Seconds to search the result n");
in.close();
}
public static void readAndFindRecordFromCSV( String filePath, String searchTerm) {
try{
HashMap<String,ArrayList<String>> cityMap = new HashMap<String,ArrayList<String>>();
Scanner x = new Scanner (new File(filePath),"UTF-8");
String city= "";
while(x.hasNextLine()) {
ArrayList<String> values = new ArrayList<String>();
String name = x.nextLine();
//break each line of the csv file to its elements
String[] line = name.split(",");
city = line[1];
for(int i=0;i<line.length;i++){
values.add(line[i]);
}
cityMap.put(city,values);
}
x.close();
//Search the city
if(cityMap.containsKey(searchTerm)) {
System.out.println("City name is : "+searchTerm+"nCity details are accordingly in the order :"
+ "n[city , city_ascii , lat , lng , country , iso2 , iso3 , admin_name , capital , population , id] n"
+cityMap.get(searchTerm)+"");
}
else {
System.out.println("Enter the correct City name");
}
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}'
时间应该优化,每次我搜索它都会读取整个文件(应该发生(
目前,您将地图初始化混合在搜索功能中。
你不想要那个。
首先,初始化地图,然后在搜索功能中使用它。
为此,请为实例化和评估映射的语句提取一个方法,然后重构readAndFindRecordFromCSV()
方法,以便它接受Map
作为附加参数:
public static void readAndFindRecordFromCSV( String filePath, String searchTerm, HashMap<String,ArrayList<String>> dataByCity) {...}
通过重构IDE功能,它应该足够简单:"提取方法",然后"更改签名"。
这是一个代码(未在运行时测试,但在编译时测试(,它将逻辑拆分为单独的任务,并且还依赖于实例方法:
public class CSVFileReaders {
private final String csvFile;
private HashMap<String, ArrayList<String>> cityMap;
private final Scanner in = new Scanner(System.in);
public static void main(String[] args) {
String filePath = "C:\worldcities1.csv";
CSVFileReaders csvFileReaders = new CSVFileReaders(filePath);
csvFileReaders.createCitiesMap();
csvFileReaders.processUserFindRequest(); // First search
csvFileReaders.processUserFindRequest(); // Second search
}
public CSVFileReaders(String csvFile) {
this.csvFile = csvFile;
}
public void createCitiesMap() {
cityMap = new HashMap<>();
try (Scanner x = new Scanner(new File(csvFile), "UTF-8")) {
String city = "";
while (x.hasNextLine()) {
ArrayList<String> values = new ArrayList<String>();
String name = x.nextLine();
//break each line of the csv file to its elements
String[] line = name.split(",");
city = line[1];
for (int i = 0; i < line.length; i++) {
values.add(line[i]);
}
cityMap.put(city, values);
}
x.close();
} catch (FileNotFoundException e) {
throw new RuntimeException(e);
}
}
public void processUserFindRequest() {
System.out.println(" n Enter the City name to be Searched : n _> ");
long start = System.currentTimeMillis();
String searchTerm = in.nextLine();
long end = System.currentTimeMillis();
System.out.println(" n It took " + (end - start) + " Milli Seconds to search the result n");
//Search the city
if (cityMap.containsKey(searchTerm)) {
System.out.println("City name is : " + searchTerm + "nCity details are accordingly in the order :"
+ "n[city , city_ascii , lat , lng , country , iso2 , iso3 , admin_name , capital , population , id] n"
+ cityMap.get(searchTerm) + "");
} else {
System.out.println("Enter the correct City name");
}
}
}
有趣的部分在这里:
String filePath = "C:\worldcities1.csv";
CSVFileReaders csvFileReaders = new CSVFileReaders(filePath);
csvFileReaders.createCitiesMap();
csvFileReaders.processUserFindRequest(); // First search
csvFileReaders.processUserFindRequest(); // Second search
逻辑现在更清楚了。
为什么每次搜索都要创建/加载CSV到HashMap中?只需在开始时只创建一次 HashMap,然后在每次搜索时只需检查它是否存在于 HashMap 中,例如将读取部分移动到单独的方法中:
HashMap<String,ArrayList<String>> cityMap = new HashMap<String,ArrayList<String>>();
public static void readCSVIntoHashMap( String filePath) {
try{
Scanner x = new Scanner (new File(filePath),"UTF-8");
String city= "";
while(x.hasNextLine()) {
ArrayList<String> values = new ArrayList<String>();
String name = x.nextLine();
//break each line of the csv file to its elements
String[] line = name.split(",");
city = line[1];
for(int i=0;i<line.length;i++){
values.add(line[i]);
}
cityMap.put(city,values);
}
x.close();
...
}
然后有一个单独的搜索方法:
public static void search(String searchTerm) {
if(cityMap.containsKey(searchTerm)) {
...
}
}