Java 如何比较两个HashMap
我想将从excel文件读取的数据与从SQL查询获得的数据进行比较。键是第1列,值是第2列,该列被放入HashMap。起初我使用HashMapJava 如何比较两个HashMap,java,excel,jdbc,hashmap,apache-poi,Java,Excel,Jdbc,Hashmap,Apache Poi,我想将从excel文件读取的数据与从SQL查询获得的数据进行比较。键是第1列,值是第2列,该列被放入HashMap。起初我使用HashMap进行比较,因为我只需要比较对,但现在我必须比较,我有点卡住了。 以下是我读取xls文件的代码: public class ReadExcel { HashMap<String, List<String>> result = new HashMap<String, List<String>>(); p
public class ReadExcel {
HashMap<String, List<String>> result = new HashMap<String, List<String>>();
public HashMap<String, List<String>> process() {
try
{
result.clear();
FileInputStream file = new FileInputStream(new File("C:/some.xlsx"));
//Create Workbook instance holding reference to .xlsx file
XSSFWorkbook workbook = new XSSFWorkbook(file);
//Get first/desired sheet from the workbook
XSSFSheet sheet = workbook.getSheetAt(0);
//Iterate through each rows one by one
Iterator<Row> rowIterator = sheet.iterator();
while (rowIterator.hasNext()) {
List<String> xlsList = new ArrayList<String>();
Row row = rowIterator.next();
Cell cell = row.getCell(1);
Cell cell2 = row.getCell(2);
String key ="";
String value="";
xlsList.clear();
switch (cell.getCellType())
{
case Cell.CELL_TYPE_NUMERIC:
key = getStringCellValue(cell);
value = getNumericCellValue(cell2);
break;
case Cell.CELL_TYPE_STRING:
key = getStringCellValue(cell);
value = getStringCellValue(cell2);
break;
}
xlsList.add(value);
result.put(key, xlsList);
}
}
}
当我运行excel阅读器时,它会在HashMap中的car键下放置蓝色、黄色的值。
例如,当我有:
row 1: column 1 = car, column 2 = blue
row 2: column 1 = car, column 2 = yellow
row 3: column 1 = year, column 2 = 1990
row 4: column 1 = year, column 2 = 1999
它仅显示:car=[黄色],year=[1999]。它只需要最后一个值,如果没有重复的关键点,它工作得很好
第一个问题:我怎样才能做得更好?如果我在第1行得到相同的键,只取一次键,并且如果第1行的键相同,则存储第2行的所有值
以下是我从SQL数据库提取数据的代码:
public class DB {
HashMap<String, List<String>> result = new HashMap<String, List<String>>();
public HashMap<String, List<String>> process() {
result.clear();
Connection conn = null;
Statement stmt = null;
List<String> carColour = new ArrayList<String>();
try {
Class.forName("oracle.jdbc.driver.OracleDriver");
conn = DriverManager.getConnection(DB_URL, USER, PASS);
stmt = conn.createStatement();
String sql1 = "SOME SQL SELECT STATEMENT THAT RETURNS 2 or more lines, by that i mean "car" has 2 values or more";
ResultSet rs = stmt.executeQuery(sql1);
while(rs.next()){
carColour.add(rs.getString("colour")); // i select the column "colour"
result.put("car", carColour); // i put "car" as key, and "blue" and "yellow" as values
...................................
}
} catch...
}
DB的代码工作正常,但是如果我想提取更多的列,比如颜色或年份,我必须为所有列创建列表,如果我要提取20列,这可能会非常耗时
第二个问题:我怎样做才能比创建20个列表更容易?使用相同的列表maybe和list.clear;信息技术这要视情况而定,因为如果我有30列,而我只需要20列,我就可以全部获取StringColumn并删除我不想要的列,但是如何删除呢
以下是用于比较的代码:
final Map<String, Boolean> comparisonResult = compareEntries(dbResult, xlsResult);
for(final Entry<String, Boolean> entry : comparisonResult.entrySet()){
if (entry.getValue() == false){
System.out.println("------------------------------------------------------------------------");
System.out.println("| Comparison FAILED | Value not matching! Column name --> " + entry.getKey() + " |");
}
}
System.out.println("------------------------------------------------------------------------");
System.out.println("DB consistency check finished.");
public static <K extends Comparable<? super K>, V>
Map<K, Boolean> compareEntries(final Map<K, V> dbResult,
final Map<K, V> xlsResult){
final Collection<K> allKeys = new HashSet<K>();
allKeys.addAll(dbResult.keySet());
allKeys.addAll(xlsResult.keySet());
final Map<K, Boolean> result = new TreeMap<K, Boolean>();
for(final K key : allKeys){
result.put(key, dbResult.containsKey(key) == xlsResult.containsKey(key) && Boolean.valueOf(equal(dbResult.get(key), xlsResult.get(key))));
}
return result;
}
private static boolean equal(final Object obj1, final Object obj2){
return obj1 == obj2 || (obj1 != null && obj1.equals(obj2));
}
最后一个问题:如何改进代码以比较两个HashMapString,List// ...
while (rowIterator.hasNext()) {
Row row = rowIterator.next();
Cell keyCell = row.getCell(1);
Cell valCell = row.getCell(2);
String key = getStringCellValue(keyCell);
switch (cell.getCellType()) {
case Cell.CELL_TYPE_NUMERIC:
value = getNumericCellValue(valCell);
break;
case Cell.CELL_TYPE_STRING:
value = getStringCellValue(valCell);
break;
}
}
// this line only compiles since Java 8
result.computeIfAbsent(key, k -> new HashSet<Object>()).add(value);
}
当然,这只会产生正确或错误。如果您想知道哪些条目不同,您需要自己来做。如果您只需要检查相等/不相等,我倾向于将两组数据转换为相同的数据类型,然后编写递归ObjectsReeQualobObject obj1,Object obj2方法来比较这两棵树。在ReadExcel的迭代器循环中,您总是在创建一个新的列表xlsList。这就是为什么每个列表最后只包含一个值的原因。也许,更方便的方法是使用SQL在DB级别处理这个问题?为什么您决定从DB导出数据,而不是将数据导入临时表并执行SQL?对于重构您的DB类,您使用spring jdbc库的开放程度如何?非常开放,如果更容易实现,这样做不会在while循环之外工作,只会在它内部工作,我仍然得到:类型不匹配无法从列表转换为集合。Set list=result.getkey;如果list==null result.putkey,则list=new HashSet;list.addvalue;这是因为结果映射的类型是HashMap,但现在应该是HashMap。
// ...
while (rowIterator.hasNext()) {
Row row = rowIterator.next();
Cell keyCell = row.getCell(1);
Cell valCell = row.getCell(2);
String key = getStringCellValue(keyCell);
switch (cell.getCellType()) {
case Cell.CELL_TYPE_NUMERIC:
value = getNumericCellValue(valCell);
break;
case Cell.CELL_TYPE_STRING:
value = getStringCellValue(valCell);
break;
}
}
// this line only compiles since Java 8
result.computeIfAbsent(key, k -> new HashSet<Object>()).add(value);
}
Set<Object> list = result.get(key);
if (list == null) result.put(key, list = new HashSet<Object>());
list.add(value);
if (map1.equals(map2)) {
// both maps are equal!
} else {
// maps are NOT equal!
}