We Keep Coding

Combine 2 array lists of objects that have null values

I'm trying to concatenate 2 array lists of objects into one but i can't figure out how to do it. I've tried with addAll and add but those methods won't really do what i want.
Basically, i have one array list with values like this:
SearchResult1 [title=null, url=null, price=19 690 EUR]
And another one with values like this:
SearchResult2 [title=Ford Car, url=http://www.something.com, price=null]
How can i combine those 2 arrays into one with values like this:
SearchResult3 [title=Ford Car, url=http://www.something.com, price=19 690 EUR]
This is the code so far:
public List searchMethod() {
try {
final String query = "ford";
final Document page = Jsoup.connect("link" + URLEncoder.encode(query, "UTF-8")).userAgent(USER_AGENT).get();
List<SearchResult> resultList1 = new ArrayList<SearchResult>();
List<SearchResult> resultList2 = new ArrayList<SearchResult>();
List<SearchResult> resultList3 = new ArrayList<SearchResult>();
for(Element searchResult : page.select(".offer-price")) {
String price = searchResult.text();
resultList1.add(new SearchResult(price));
}
for(Element searchResult : page.select(".offer-title__link")) {
String title = searchResult.text();
String url = searchResult.attr("href");
resultList2.add(new SearchResult(title, url));
}
resultList3.addAll(resultList1);
resultList3.addAll(resultList2);
return resultList3;
}catch(Exception e) {
e.printStackTrace();
}
return Collections.emptyList();
}
The values that i put in those arrays are extracted from a web page
Thanks for helping!

From the comment, you have said that you just want to correlate/merge the objects from both lists by each index.
You can simply loop through the list, constructing a new SearchResult (assuming you have getters for the fields)
for(int i = 0; i < resultList1.size(); i++) {
resultList3.add(new SearchResult(resultList1.get(i).getPrice(),
resultList2.get(i).getTitle(),
resultList2.get(i).getUrl()));
}
You may have to change the order of the passed arguments to the SearchResult constructor taking price, title and url as you haven't shown it.

why don't you do it in one shot?
List<SearchResult> resultList1 = new ArrayList<SearchResult>();
for(Element searchResult : page.select(".offer-title__link")) {
String title = searchResult.text();
String url = searchResult.attr("href");
resultList1.add(new SearchResult(title, url));
}
int index = 0;
for(Element searchResult : page.select(".offer-price")) {
String price = searchResult.text();
//since you have already assumed
//that price will come in the same order and title and url.
resultList1.get(index++).setPrice(price);
}
return resultList1;

How to Loop next element in hashmap

I have a set of strings like this
A_2007-04, A_2007-09, A_Agent, A_Daily, A_Execute, A_Exec, B_Action, B_HealthCheck
I want output as:
Key = A, Value = [2007-04,2007-09,Agent,Execute,Exec]
Key = B, Value = [Action,HealthCheck]
I'm using HashMap to do this
pckg:{A,B}
count:total no of strings
reports:set of strings
Logic I used is nested loop:
for (String l : reports[i]) {
for (String r : pckg) {
String[] g = l.split("_");
if (g[0].equalsIgnoreCase(r)) {
report.add(g[1]);
dirFiles.put(g[0], report);
} else {
break;
}
}
}
I'm getting output as
Key = A, Value = [2007-04,2007-09,Agent,Execute,Exec]
How to get second key?
Can someone suggest logic for this?

Assuming that you use Java 8, it can be done using computeIfAbsent to initialize the List of values when it is a new key as next:
List<String> tokens = Arrays.asList(
"A_2007-04", "A_2007-09", "A_Agent", "A_Daily", "A_Execute",
"A_Exec", "P_Action", "P_HealthCheck"
);
Map<String, List<String>> map = new HashMap<>();
for (String token : tokens) {
String[] g = token.split("_");
map.computeIfAbsent(g[0], key -> new ArrayList<>()).add(g[1]);
}

In terms of raw code this should do what I think you are trying to achieve:
// Create a collection of String any way you like, but for testing
// I've simply split a flat string into an array.
String flatString = "A_2007-04,A_2007-09,A_Agent,A_Daily,A_Execute,A_Exec,"
+ "P_Action,P_HealthCheck";
String[] reports = flatString.split(",");
Map<String, List<String>> mapFromReportKeyToValues = new HashMap<>();
for (String report : reports) {
int underscoreIndex = report.indexOf("_");
String key = report.substring(0, underscoreIndex);
String newValue = report.substring(underscoreIndex + 1);
List<String> existingValues = mapFromReportKeyToValues.get(key);
if (existingValues == null) {
// This key hasn't been seen before, so create a new list
// to contain values which belong under this key.
existingValues = new ArrayList<>();
mapFromReportKeyToValues.put(key, existingValues);
}
existingValues.add(newValue);
}
System.out.println("Generated map:\n" + mapFromReportKeyToValues);
Though I recommend tidying it up and organising it into a method or methods as fits your project code.

Doing this with Map<String, ArrayList<String>> will be another good approach I think:
String reports[] = {"A_2007-04", "A_2007-09", "A_Agent", "A_Daily",
"A_Execute", "A_Exec", "P_Action", "P_HealthCheck"};
Map<String, ArrayList<String>> map = new HashMap<>();
for (String rep : reports) {
String s[] = rep.split("_");
String prefix = s[0], suffix = s[1];
ArrayList<String> list = new ArrayList<>();
if (map.containsKey(prefix)) {
list = map.get(prefix);
}
list.add(suffix);
map.put(prefix, list);
}
// Print
for (Map.Entry<String, ArrayList<String>> entry : map.entrySet()) {
String key = entry.getKey();
ArrayList<String> valueList = entry.getValue();
System.out.println(key + " " + valueList);
}

for (String l : reports[i]) {
String[] g = l.split("_");
for (String r : pckg) {
if (g[0].equalsIgnoreCase(r)) {
report = dirFiles.get(g[0]);
if(report == null){ report = new ArrayList<String>(); } //create new report
report.add(g[1]);
dirFiles.put(g[0], report);
}
}
}
Removed the else part of the if condition. You are using break there which exits the inner loop and you never get to evaluate the keys beyond first key.
Added checking for existing values. As suggested by Orin2005.
Also I have moved the statement String[] g = l.split("_"); outside inner loop so that it doesn't get executed multiple times.

Java sanitizing Arraylist records suggestions

I am looking for an idea how to accomplish this task. So I'll start with how my program is working.
My program reads a CSV file. They are key value pairs separated by a comma.
L1234456,ygja-3bcb-iiiv-pppp-a8yr-c3d2-ct7v-giap-24yj-3gie
L6789101,zgna-3mcb-iiiv-pppp-a8yr-c3d2-ct7v-gggg-zz33-33ie
etc
Function takes a file and parses it into an arrayList of String[]. The function returns the ArrayList.
public ArrayList<String[]> parseFile(File csvFile) {
Scanner scan = null;
try {
scan = new Scanner(csvFile);
} catch (FileNotFoundException e) {
}
ArrayList<String[]> records = new ArrayList<String[]>();
String[] record = new String[2];
while (scan.hasNext()) {
record = scan.nextLine().trim().split(",");
records.add(record);
}
return records;
}
Here is the code, where I am calling parse file and passing in the CSVFile.
ArrayList<String[]> Records = parseFile(csvFile);
I then created another ArrayList for files that aren't parsed.
ArrayList<String> NotParsed = new ArrayList<String>();
So the program then continues to sanitize the key value pairs separated by a comma. So we first start with the first key in the record. E.g L1234456. If the record could not be sanitized it then it replaces the current key with "CouldNOtBeParsed" text.
for (int i = 0; i < Records.size(); i++) {
if(!validateRecord(Records.get(i)[0].toString())) {
Logging.info("Records could not be parsed " + Records.get(i)[0]);
NotParsed.add(srpRecords.get(i)[0].toString());
Records.get(i)[0] = "CouldNotBeParsed";
} else {
Logging.info(Records.get(i)[0] + " has been sanitized");
}
}
Next we do the 2nd key in the key value pair e.g ygja-3bcb-iiiv-pppp-a8yr-c3d2-ct7v-giap-24yj-3gie
for (int i = 0; i < Records.size(); i++) {
if(!validateRecordKey(Records.get(i)[1].toString())) {
Logging.info("Record Key could not be parsed " + Records.get(i)[0]);
NotParsed.add(Records.get(i)[1].toString());
Records.get(i)[1] = "CouldNotBeParsed";
} else {
Logging.info(Records.get(i)[1] + " has been sanitized");
}
}
The problem is that I need both keyvalue pairs to be sanitized, make a separate list of the keyValue pairs that could not be sanitized and a list of the ones there were sanitized so they can be inserted into a database. The ones that cannot will be printed out to the user.
I thought about looping thought the records and removing the records with the "CouldNotBeParsed" text so that would just leave the ones that could be parsed. I also tried removing the records from the during the for loop Records.remove((i)); However that messes up the For loop because if the first record could not be sanitized, then it's removed, the on the next iteration of the loop it's skipped because record 2 is now record 1. That's why i went with adding the text.
Atually I need two lists, one for the Records that were sanitized and another that wasn't.
So I was thinking there must be a better way to do this. Or a better method of sanitizing both keyValue pairs at the same time or something of that nature. Suggestions?

Start by changing the data structure: rather than using a list of two-element String[] arrays, define a class for your key-value pairs:
class KeyValuePair {
private final String key;
private final String value;
public KeyValuePair(String k, String v) { key = k; value = v; }
public String getKey() { return key; }
public String getValue() { return value; }
}
Note that the class is immutable.
Now make an object with three lists of KeyValuePair objects:
class ParseResult {
private final List<KeyValuePair> sanitized = new ArrayList<KeyValuePair>();
private final List<KeyValuePair> badKey = new ArrayList<KeyValuePair>();
private final List<KeyValuePair> badValue = new ArrayList<KeyValuePair>();
public ParseResult(List<KeyValuePair> s, List<KeyValuePair> bk, List<KeyValuePair> bv) {
sanitized = s;
badKey = bk;
badValue = bv;
}
public List<KeyValuePair> getSanitized() { return sanitized; }
public List<KeyValuePair> getBadKey() { return badKey; }
public List<KeyValuePair> getBadValue() { return badValue; }
}
Finally, populate these three lists in a single loop that reads from the file:
public static ParseResult parseFile(File csvFile) {
Scanner scan = null;
try {
scan = new Scanner(csvFile);
} catch (FileNotFoundException e) {
???
// Do something about this exception.
// Consider not catching it here, letting the caller deal with it.
}
final List<KeyValuePair> sanitized = new ArrayList<KeyValuePair>();
final List<KeyValuePair> badKey = new ArrayList<KeyValuePair>();
final List<KeyValuePair> badValue = new ArrayList<KeyValuePair>();
while (scan.hasNext()) {
String[] tokens = scan.nextLine().trim().split(",");
if (tokens.length != 2) {
???
// Do something about this - either throw an exception,
// or log a message and continue.
}
KeyValuePair kvp = new KeyValuePair(tokens[0], tokens[1]);
// Do the validation on the spot
if (!validateRecordKey(kvp.getKey())) {
badKey.add(kvp);
} else if (!validateRecord(kvp.getValue())) {
badValue.add(kvp);
} else {
sanitized.add(kvp);
}
}
return new ParseResult(sanitized, badKey, badValue);
}
Now you have a single function that produces a single result with all your records cleanly separated into three buckets - i.e. sanitized records, records with bad keys, and record with good keys but bad values.

Changing HashMap keys during iteration

is it possible to change keys of a the same HashMap instance during iteration ? Because map entry set don't have a method entry.setKey(). Now what I can think off is create another HashMap...
MultipartParsingResult parsingResult = parseRequest(request);
Map<String, String[]> mpParams = parsingResult.getMultipartParameters();
Map<String, String[]> mpParams2 = new HashMap<String, String[]>();
Iterator<Entry<String,String[]>> it = mpParams.entrySet().iterator();
while (it.hasNext()) {
Entry<String,String[]> entry = it.next();
String name = entry.getKey();
if (name.startsWith(portletNamespace)) {
mpParams2.put(name.substring(portletNamespace.length(), name.length()), entry.getValue());
}
else {
mpParams2.put(name, entry.getValue());
}
}

Maybe this helps:
map.put(newkey,map.remove(oldkey));

You should keep information in other collection to modify it after iteration. You can only remove entry using iterator.remove() during iterator. HashMap contract forbids mutating it during iteration.

There are four common types of modification you might want to do to the keys or values in a HashMap.
To change a HashMap key, you look up the value object with get, then remove the old key and put it with the new key.
To change the fields in a value object, look the value object up by key with get, then use its setter methods.
To replace the value object in its entirely, just put a new value object at the old key.
To replace the value object with one based on the old, look the value object up with get, create a new object, copy data over from the old one, then put the new object under the same key.
Something like this example.
static class Food
{
// ------------------------------ FIELDS ------------------------------
String colour;
String name;
float caloriesPerGram;
// -------------------------- PUBLIC INSTANCE METHODS --------------------------
public float getCaloriesPerGram()
{
return caloriesPerGram;
}
public void setCaloriesPerGram( final float caloriesPerGram )
{
this.caloriesPerGram = caloriesPerGram;
}
public String getColour()
{
return colour;
}
public void setColour( final String colour )
{
this.colour = colour;
}
public String getName()
{
return name;
}
public void setName( final String name )
{
this.name = name;
}
public String toString()
{
return name + " : " + colour + " : " + caloriesPerGram;
}
// --------------------------- CONSTRUCTORS ---------------------------
Food( final String name, final String colour, final float caloriesPerGram )
{
this.name = name;
this.colour = colour;
this.caloriesPerGram = caloriesPerGram;
}
}
// --------------------------- main() method ---------------------------
/**
* Sample code to TEST HashMap Modifying
*
* #param args not used
*/
public static void main( String[] args )
{
// create a new HashMap
HashMap<String, Food> h = new HashMap<String, Food>( 149
/* capacity */,
0.75f
/* loadfactor */ );
// add some Food objecs to the HashMap
// see http://www.calorie-charts.net for calories/gram
h.put( "sugar", new Food( "sugar", "white", 4.5f ) );
h.put( "alchol", new Food( "alcohol", "clear", 7.0f ) );
h.put( "cheddar", new Food( "cheddar", "orange", 4.03f ) );
h.put( "peas", new Food( "peas", "green", .81f ) );
h.put( "salmon", new Food( "salmon", "pink", 2.16f ) );
// (1) modify the alcohol key to fix the spelling error in the key.
Food alc = h.get( "alchol" );
h.put( "alcohol", alc );
h.remove( "alchol" );
// (2) modify the value object for sugar key.
Food sug = h.get( "sugar" );
sug.setColour( "brown" );
// do not need to put.
// (3) replace the value object for the cheddar key
// don't need to get the old value first.
h.put( "cheddar", new Food( "cheddar", "white", 4.02f ) );
// (4) replace the value object for the peas key with object based on previous
Food peas = h.get( "peas" );
h.put( "peas", new Food( peas.getName(), peas.getColour(), peas.getCaloriesPerGram() * 1.05f ) );
// enumerate all the keys in the HashMap in random order
for ( String key : h.keySet() )
{
out.println( key + " = " + h.get( key ).toString() );
}
}// end main
}
I hope this helps

i got to this thread when i needed to change the keys of the map entries.
in my case i have a JSON representation in a Map , meaning it can hold map or list of maps, here is the code:
private Map<String,Object> changeKeyMap(Map<String, Object> jsonAsMap) throws InterruptedException {
Map<String,Object> mapClone = new LinkedHashMap<>();
for (Map.Entry<String, Object> entry : jsonAsMap.entrySet()) {
if (Thread.currentThread().isInterrupted()) throw new InterruptedException();
Object value = entry.getValue();
if (entry.getValue() instanceof Map) {
value = changeKeyMap((Map) entry.getValue());
} else if (isListOfMaps(entry.getValue())) {
value = changeKeyListOfMaps((List<Map<String, Object>>) entry.getValue());
}
String changedKey = changeSingleKey(entry.getKey());
mapClone.put(changedKey, value);
}
return mapClone;
}
private List<Map<String,Object>> changeKeyListOfMaps(List<Map<String,Object>> listOfMaps) throws InterruptedException {
List<Map<String,Object>> newInnerMapList = new ArrayList<>();
for(Object singleMapFromArray :listOfMaps){
Map<String,Object> changeKeyedMap = changeKeyMap((Map<String, Object>) singleMapFromArray);
newInnerMapList.add(changeKeyedMap);
}
return newInnerMapList;
}
private boolean isListOfMaps(Object object) {
return object instanceof List && !((List) object).isEmpty() && ((List) object).get(0) instanceof Map;
}
private String changeSingleKey(String originalKey) {
return originalKey + "SomeChange"
}

The best thing to do is to copy the map into a new one with the modifications you want, then return this new maps and destroy the old one.
I wonder what's the performance impact of this solution however.

Query String Manipulation in Java

Does anyone have, or know of, a java class that I can use to manipulate query strings?
Essentially I'd like a class that I can simply give a query string to and then delete, add and modify query string KVP's.
Thanks in advance.
EDIT
In response to a comment made to this question, the query string will look something like this;
N=123+456+112&Ntt=koala&D=abc
So I'd like to pass this class the query string and say something like;
String[] N = queryStringClass.getParameter("N");
and then maybe
queryStringClass.setParameter("N", N);
and maybe queryStringClass.removeParameter("N");
Or something to that effect.

SOmething like this
public static Map<String, String> getQueryMap(String query)
{
String[] params = query.split("&");
Map<String, String> map = new HashMap<String, String>();
for (String param : params)
{
String name = param.split("=")[0];
String value = param.split("=")[1];
map.put(name, value);
}
return map;
}
To iterate the map simply:
String query = url.getQuery();
Map<String, String> map = getQueryMap(query);
Set<String> keys = map.keySet();
for (String key : keys)
{
System.out.println("Name=" + key);
System.out.println("Value=" + map.get(key));
}

You can also use Google Guava's Splitter.
String queryString = "variableA=89&variableB=100";
Map<String,String> queryParameters = Splitter
.on("&")
.withKeyValueSeparator("=")
.split(queryString);
System.out.println(queryParameters.get("variableA"));
prints out
89
This I think is a very readable alternative to parsing it yourself.
Edit: As #raulk pointed out, this solution does not account for escaped characters. However, this may not be an issue because before you URL-Decode, the query string is guaranteed to not have any escaped characters that conflict with '=' and '&'. You can use this to your advantage in the following way.
Say that you must decode the following query string:
a=%26%23%25!)%23(%40!&b=%23%24(%40)%24%40%40))%24%23%5E*%26
which is URL encoded, then you are guaranteed that the '&' and '=' are specifically used for separating pairs and key from value, respectively, at which point you can use the Guava splitter to get:
a = %26%23%25!)%23(%40!
b = %23%24(%40)%24%40%40))%24%23%5E*%26
Once you have obtained the key-value pairs, then you can URL decode them separately.
a = &#%!)#(#!
b = #$(#)$##))$#^*&
That should cover all cases.

If you are using J2EE, you can use ServletRequest.getParameterValues().
Otherwise, I don't think Java has any common classes for query string handling. Writing your own shouldn't be too hard, though there are certain tricky edge cases, such as realizing that technically the same key may appear more than once in the query string.
One implementation might look like:
import java.util.*;
import java.net.URLEncoder;
import java.net.URLDecoder;
public class QueryParams {
private static class KVP {
final String key;
final String value;
KVP (String key, String value) {
this.key = key;
this.value = value;
}
}
List<KVP> query = new ArrayList<KVP>();
public QueryParams(String queryString) {
parse(queryString);
}
public QueryParams() {
}
public void addParam(String key, String value) {
if (key == null || value == null)
throw new NullPointerException("null parameter key or value");
query.add(new KVP(key, value));
}
private void parse(String queryString) {
for (String pair : queryString.split("&")) {
int eq = pair.indexOf("=");
if (eq < 0) {
// key with no value
addParam(URLDecoder.decode(pair), "");
} else {
// key=value
String key = URLDecoder.decode(pair.substring(0, eq));
String value = URLDecoder.decode(pair.substring(eq + 1));
query.add(new KVP(key, value));
}
}
}
public String toQueryString() {
StringBuilder sb = new StringBuilder();
for (KVP kvp : query) {
if (sb.length() > 0) {
sb.append('&');
}
sb.append(URLEncoder.encode(kvp.key));
if (!kvp.value.equals("")) {
sb.append('=');
sb.append(URLEncoder.encode(kvp.value));
}
}
return sb.toString();
}
public String getParameter(String key) {
for (KVP kvp : query) {
if (kvp.key.equals(key)) {
return kvp.value;
}
}
return null;
}
public List<String> getParameterValues(String key) {
List<String> list = new LinkedList<String>();
for (KVP kvp : query) {
if (kvp.key.equals(key)) {
list.add(kvp.value);
}
}
return list;
}
public static void main(String[] args) {
QueryParams qp = new QueryParams("k1=v1&k2&k3=v3&k1=v4&k1&k5=hello+%22world");
System.out.println("getParameter:");
String[] keys = new String[] { "k1", "k2", "k3", "k5" };
for (String key : keys) {
System.out.println(key + ": " + qp.getParameter(key));
}
System.out.println("getParameters(k1): " + qp.getParameterValues("k1"));
}
}

Another way is to use apache http-components. It's a bit hacky, but at least you leverage all the parsing corner cases:
List<NameValuePair> params =
URLEncodedUtils.parse("http://example.com/?" + queryString, Charset.forName("UTF-8"));
That'll give you a List of NameValuePair objects that should be easy to work with.

You can create a util method and use regular expression to parse it. A pattern like "[;&]" should suffice.