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How to apply for loop on first n vlalues of arraylist

I have an arraylist in which I have ESSID, BSSID, Strenght of access Point on first three indexes, and from Index 4 to 6 I have again ESSID, BSSID, Strength of another AccessPoint. I want to store this list in database like first three values save in one row of table. and next three values save in 2nd row of table.
String[] namesArr = new String[arrayList2.size()]; //conver arraylist to array
for (int j = 0; j < arrayList2.size(); j++){
namesArr[j] = arrayList2.get(j);
int length = namesArr[j].length();
for (int k = 0; k < length; k += 3) {
ssid = namesArr[k];
bssid = namesArr[k + 1];
rssid = namesArr[k + 2];
}
insertValues(this);
}
public void insertValues(View.OnClickListener view){
SendData send = new SendData(this);
send.execute(bssid,ssid,rssid);}
I have made a class to store this data in database that works fine.
public class SendData extends AsyncTask<String, Void, String> {
AlertDialog dialog;
Context context;
public SendData(Context context) {
this.context = context;
}
#Override
protected void onPreExecute() {
dialog = new AlertDialog.Builder(context).create();
dialog.setTitle("Message");
}
#Override
protected void onPostExecute(String s) {
dialog.setMessage(s);
dialog.show();
}
#Override
protected String doInBackground(String... voids) {
String data = "";
String result = "";
String MAC = voids[0];
String Name = voids[1];
String Strength = voids[2];
String con_Str = "http://10.5.48.129/Webapi/accesspoints_data/create.php";
try{
URL url = new URL(con_Str);
HttpURLConnection http = (HttpURLConnection) url.openConnection();
http.setRequestMethod("POST");
http.setDoInput(true);
http.setDoOutput(true);
OutputStream out_Stream = http.getOutputStream();
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(out_Stream, "UTF-8"));
JSONObject obj = new JSONObject();
try {
obj.put("BSSID", MAC);
obj.put("ESSID", Name);
obj.put("RSSID", Strength);
} catch (JSONException e) {
e.printStackTrace();
}
data = obj.toString();
writer.write(data);
writer.flush();
writer.close();
out_Stream.close();
InputStream in_Stream = http.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(in_Stream, "ISO-8859-1"));
String line = "";
while ((line = reader.readLine()) != null)
{
result += line;
}
reader.close();
in_Stream.close();
http.disconnect();
return result;
} catch (MalformedURLException e){
result = e.getMessage();
} catch (IOException e){
result = e.getMessage();
}
return result;
}
}
SendData class is perfectly working but problem is with for loop.

I think this is result that you are expecting :
List<String> arrayList2 = new ArrayList<>();
arrayList2.add("1");
arrayList2.add("2");
arrayList2.add("3");
arrayList2.add("4");
arrayList2.add("5");
arrayList2.add("6");
arrayList2.add("6");
arrayList2.add("7");
arrayList2.add("8");
arrayList2.add("9");
arrayList2.add("10");
List<String[]> sarrayList = new ArrayList<>();
String[] arr = new String[3];
int i = 0;
for (int j = 0; j < arrayList2.size(); j++)
{
arr[i] = arrayList2.get(j);
i++;
if((j+1)%3==0)
{
sarrayList.add(arr);
i = 0;
arr = new String[3];
}
}
for(String [] sa:sarrayList)
{
for(String s:sa)
{
System.out.println(s);
}
System.out.println("=========");
}
This might not be the most efficient way of doing it. But it splits the ArrayList in to String arrays of length=3 and stores them in a new ArrayList named sarrayList

I would advise to use a datastructure to hold the record. See the code below this is a small example how you could do it
ArrayList<Record> records;
for (int i = 2; i < inputArrayList.size(); i = i + 3){
string ssid = namesArr.get(i - 2);
string bssid = namesArr.get(i - 1);
string rssid = namesArr.get(i);
records.add(new Record(ssid, bssid, rssid));
}
class Record{
string ssid;
string bssid;
string rssid;
// Constructor...
// Getter and setter to be implemented...
}

ok from what i understand you want to divide the arraylist each 3 elements thats how you do it with streams and it will return an a collection of arraylists each one has 3 elements
final int chunkSize = 3;
final AtomicInteger counter = new AtomicInteger();
//arrayList here us your array list
final Collection<List<String>> result = arrayList.stream()
.collect(Collectors.groupingBy(it -> counter.getAndIncrement() / chunkSize))
.values();
and mentioning supermar10 answer you code make a class to map the strings to it like that
class Record{
string ssid;
string bssid;
string rssid;
Record(String ssid,String bssid,String rssid){
this.ssid=ssid;
this.bssid=bssid;
this.rssid=rssid;
}
}
now you have a class to map to now save the records in a list of Record
create a a list in the main class
static List<Record> lists=new ArrayList<>();
then map the data like that
result.stream().forEach(nowList -> saveRecord(nowList));
and thats the save method
static void saveRecord(List<String> list){
lists.add(new Record(list.get(0),list.get(1),list.get(2)));
}

I have simplified it to one loop and also modified insertValues so that it takes 3 more parameters. This
int size = arrayList2.size();
for (int j = 0; j < size; j += 3) {
if (size - j < 3 ) {
break;
}
String ssid = arrayList2.get(j);
String bssid = arrayList2.get(j + 1);
String rssid = arrayList2.get(j + 2);
insertValues(this, ssid, bssid, rssid);
}
if one the other hand ssid and so on are class variables the inside of the loop can be changed to
ssid = arrayList2.get(j);
bssid = arrayList2.get(j + 1);
rssid = arrayList2.get(j + 2);
insertValues();

read json with timestamps as jsonobject keys

I am trying to log weather data for a university hydrological project using java.
The data is formated as a json file in 5 minute intervals for the last 24 hours in the following way (example):
{
"1482439800":{
"hu":92,
"te":-2.9,
"dp":-4.5,
"pr":1028.4,
"pa":null,
"ws":1.4,
"wd":180
},
"1482440100":{
"hu":92,
"te":-2.9,
"dp":-4.5,
"pr":1028.4,
"pa":null,
"ws":1.4,
"wd":180
}
}
I have already tried to use the following code to access data from the json file:
private static String readUrl(String urlString) throws Exception {
BufferedReader reader = null;
try {
URL url = new URL(urlString);
reader = new BufferedReader(new InputStreamReader(url.openStream()));
StringBuffer buffer = new StringBuffer();
int read;
char[] chars = new char[1024];
while ((read = reader.read(chars)) != -1)
buffer.append(chars, 0, read);
return buffer.toString();
} finally {
if (reader != null)
reader.close();
}
}
public static Object[][] getstation1(){
Object[][] data = null;
try {
JSONObject json = new JSONObject(readUrl("http://netzwerk.wetter.com/api/stationdata/14091/24/"));
Iterator keys = json.keys();
while (keys.hasNext()) {
Object key = keys.next();
JSONObject value = json.getJSONObject((String) key);
double hu = value.getDouble("hu");
System.out.println(hu);
}
} catch (JSONException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
return data;
}
This was somewhat successful as it returned data for humidity (hu) but in a seemingly random order.
Now for my question: How do I read the times and return them alongside the corresponding weather data from newest to oldest inside the Object[][]?
Any help is appreciated.
Thank you.

A sorted map would be more appropriate than an Object[][].
Quickly:
TreeMap<String, Object> sorted = new TreeMap<>(json.toMap());
But that will sort alphanumerically (probably fine in your case as the timestamps are all the same length).
You could do a little more work to sort the results into a typed map:
TreeMap<Date, Map<String, Double>> byDate = json.toMap().entrySet().stream()
.collect(Collectors.toMap(
e -> new Date(Long.valueOf(e.getKey()) * 1000),
e -> (Map) e.getValue(),
(a, b) -> {throw new IllegalArgumentException("Duplicate key " + a);},
TreeMap::new
));
If you really need an Object[][] you can remap your data once it's sorted:
Object[][] data = sorted.entrySet().stream().map(e -> new Object[] {e.getKey(), e.getValue()}).toArray(Object[][]::new);
Or consider using an object mapper like jackson or gson.

Thanks for the answer but in the end I decided to go a slightly simpler route.
I retrieved all the key names, sorted them and then read the corresponding data key by key. And as I was getting frequent errors because of data being null I added protection for that as well (I need them as actual numbers).
public static Object[][] getstation1(){
Object[][] data = null;
try {
JSONObject json = new JSONObject(readUrl("http://netzwerk.wetter.com/api/stationdata/14091/2/"));
System.out.println("Fetching "+"http://netzwerk.wetter.com/api/stationdata/14091/2/");
String[] times = json.getNames(json);
Arrays.sort(times);
data = new Object[times.length][8];
for (int i = 0; i < times.length; i++){
Date temp = new Date((long)Integer.parseInt(times[i])*1000);
data[i][0] = temp;
if (json.getJSONObject(times[i]).isNull("hu")){
data[i][1] = 0;
} else {
data[i][1] = json.getJSONObject(times[i]).getDouble("hu");
}
if (json.getJSONObject(times[i]).isNull("te")){
data[i][2] = 0;
} else {
data[i][2] = json.getJSONObject(times[i]).getDouble("te");
}
if (json.getJSONObject(times[i]).isNull("dp")){
data[i][3] = 0;
} else {
data[i][3] = json.getJSONObject(times[i]).getDouble("dp");
}
if (json.getJSONObject(times[i]).isNull("pr")){
data[i][4] = 0;
} else {
data[i][4] = json.getJSONObject(times[i]).getDouble("pr");
}
if (json.getJSONObject(times[i]).isNull("pa")){
data[i][5] = 0;
} else {
data[i][5] = json.getJSONObject(times[i]).getDouble("pa");
}
if (json.getJSONObject(times[i]).isNull("ws")){
data[i][6] = 0;
} else {
data[i][6] = json.getJSONObject(times[i]).getDouble("ws");
}
if (json.getJSONObject(times[i]).isNull("wd")){
data[i][7] = 0;
} else {
data[i][7] = json.getJSONObject(times[i]).getDouble("wd");
}
}
} catch (JSONException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
return data;
}

How to copy resultset into object?

I am using the following to add retrieved values to the class. all values will be added to attributes of the class but I am using compisition ( have an object of class in the class) and it does not show anything on output.
class employee
{
....
private Address address = new Address();
.....
}
...
Employee emp = new Employee();
try {
ps = con.prepareStatement("select * from employee,address "
+ "WHERE employee.username = ? AND "
+ "employee.ADD_ID = address.ID");
ps.setString(1, username);
ResultSet r = ps.executeQuery();
if (r.next()) {
BeanProcessor bp = new BeanProcessor();
emp = bp.toBean(r,Employee.class);
System.out.println("blockkkk:"+emp.getAddress().getBlock());
//output of above line is blockkkk:null
}
con.close();
ps.close();
} catch (SQLException e) {
System.err.println(e.getMessage());
}
return emp;
Address class is as following:
public class Address {
.....
private String block;
....
public String getBlock() {
return block;
}
public void setBlock(String block) {
this.block = block;
}
....
}

The BeanProcessor.toBean works like this:
Convert a ResultSet row into a JavaBean. This implementation uses reflection and BeanInfo classes to match column names to bean property names. Properties are matched to columns based on several factors:
The class has a writable property with the same name as a column. The name comparison is case insensitive.
The column type can be converted to the property's set method parameter type with a ResultSet.get* method. If the conversion fails (ie. the property was an int and the column was a Timestamp) an SQLException is thrown.
Primitive bean properties are set to their defaults when SQL NULL is returned from the ResultSet. Numeric fields are set to 0 and booleans are set to false. Object bean properties are set to null when SQL NULL is returned. This is the same behavior as the ResultSet get* methods.
May be the address is not a writable property. Pls do check it.

public static Object copyFromResultSet(Class clazz, ResultSet resultSet)
{
ArrayList objectArrayList = new ArrayList(1);
try
{
Object object = clazz.newInstance();
objectArrayList.add(object);
copyFromResultSet(objectArrayList, resultSet);
}
catch (Exception e)
{
e.printStackTrace();
}
return objectArrayList.get(0);
}
then:
public static void copyFromResultSet(ArrayList<Object> objectArrayList, ResultSet resultSet)
{
ArrayList arrayList = null;
try
{
if (objectArrayList != null)
{
int objectArrayList_len = objectArrayList.size();
int objectArrayList_index = 0;
java.beans.BeanInfo toBeanInfo[] = new java.beans.BeanInfo[objectArrayList_len];
Vector<Method> objectMethodVector[] = new Vector[objectArrayList_len];
Vector<Type> objectTypeVector[] = new Vector[objectArrayList_len];
int totalMethod[] = new int[objectArrayList_len];
int[][] indexes = new int[objectArrayList_len][];
for (objectArrayList_index = 0; objectArrayList_index < objectArrayList_len; objectArrayList_index++)
{
toBeanInfo[objectArrayList_index] = java.beans.Introspector.getBeanInfo(objectArrayList.get(objectArrayList_index).getClass());
}
if (objectArrayList_len > 0 && resultSet != null)
{
Method method = null;
Type type[] = null;
int cols = 0;
String colName = null;
for (objectArrayList_index = 0; objectArrayList_index < objectArrayList_len; objectArrayList_index++)
{
//toBeanInfo[objectArrayList_index]=java.beans.Introspector.getBeanInfo(objectArrayList.get(objectArrayList_index).getClass());
java.beans.PropertyDescriptor toPropertyDescriptor[] = toBeanInfo[objectArrayList_index].getPropertyDescriptors();
int toPropertyDescriptor_length = toPropertyDescriptor.length;
method = null;
type = null;
ResultSetMetaData resultSetMetaData = resultSet.getMetaData();
cols = resultSetMetaData.getColumnCount();
colName = null;
Vector<Method> methodVector = new Vector(cols);
Vector<Type> typeVector = new Vector(cols);
indexes[objectArrayList_index] = new int[cols];
totalMethod[objectArrayList_index] = -1;
for (int i = 1; i <= cols; i++)
{
colName = resultSetMetaData.getColumnName(i);
for (int j = 0; j < toPropertyDescriptor_length; j++)
{
if (toPropertyDescriptor[j].getName().equalsIgnoreCase(colName))
{
totalMethod[objectArrayList_index]++;
method = toPropertyDescriptor[j].getWriteMethod();
type = method.getGenericParameterTypes();
methodVector.add(method);
typeVector.add(type[0]);
indexes[objectArrayList_index][totalMethod[objectArrayList_index]] = i;
break;
}
}
}
objectMethodVector[objectArrayList_index] = (methodVector);
objectTypeVector[objectArrayList_index] = (typeVector);
}
if (resultSet.next())
{
arrayList = new ArrayList();
for (objectArrayList_index = 0; objectArrayList_index < objectArrayList_len; objectArrayList_index++)
{
for (int i = 0; i <= totalMethod[objectArrayList_index]; i++)
{
//System.out.println(objectMethodVector[objectArrayList_index].get(i));
objectMethodVector[objectArrayList_index].get(i).invoke(objectArrayList.get(objectArrayList_index), getObject(indexes[objectArrayList_index][i], objectTypeVector[objectArrayList_index].get(i), resultSet));
}
arrayList.add(objectArrayList.get(objectArrayList_index));
}
}
while (resultSet.next())
{
for (objectArrayList_index = 0; objectArrayList_index < objectArrayList_len; objectArrayList_index++)
{
for (int i = 0; i <= totalMethod[objectArrayList_index]; i++)
{
objectMethodVector[objectArrayList_index].get(i).invoke(objectArrayList.get(objectArrayList_index), getObject(indexes[objectArrayList_index][i], objectTypeVector[objectArrayList_index].get(i), resultSet));
}
arrayList.add(objectArrayList.get(objectArrayList_index));
}
}
}
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
just copy paste this code call method copyFromResultSet(class, ResultSet )
pass two perameters first is class name and second is resultset.
i am sure this is working properlly

Eclipse warning about NullPointer Access - Android

I am trying to retrieve the UID of a Mifare Classic 1k card, and for that I use this code:
private String getUID(){
MifareClassic mfc = MifareClassic.get((Tag) intent.getParcelableExtra(NfcAdapter.EXTRA_TAG));
byte[] data;
byte[] sevenDigits = null;
String uid;
try{
mfc.connect();
boolean auth = false;
auth = mfc.authenticateSectorWithKeyA(0, MifareClassic.KEY_DEFAULT);
if(auth){
data = mfc.readBlock(mfc.sectorToBlock(0));
for (int i =0; i < 8; i++){
sevenDigits[i] = data[i];
}
return getHexString(sevenDigits);
} else {
return "Authenticatie mislukt";
}
} catch (IOException e) {
return null;
}
}
Eclipse keeps giving me a warning about this line
for (int i = 0; i < 8; i++) {
sevenDigits[i] = data[i];
}
, saying that it can only be null at that point... My question is: how do i rewrite this code so that this warning goes away?

sevenDigits
is defined as null and not modified. You probably need to call
sevenDigits = new byte[data.length];
before the loop

You declare the sevenDigits[] as null you must initialize this by its size before you used it
sevenDigits[] = new byte[size];
do not use the static value in iterator for length use the length of array which you want to use in that for loop
data = mfc.readBlock(mfc.sectorToBlock(0));
sevenDigits[] = new byte[data.length];
for (int i =0; i < data.length; i++){
sevenDigits[i] = data[i];
}

How to convert serialClob to String format?

I am trying to convert serialclob to string. But I am not successful. I think I am not doing in the correct way. My code is:
char[] buffer;
int count = 0;
int length = 0;
String data = null;
String[] type;
StringBuffer sb;
try{
SqlRowSet rows = getJdbcTemplate().queryForRowSet("select c.BOUNDING_BOX.GET_WKT() BOUNDING_BOX FROM EXAMPLE c WHERE EXAMPLE_ID = 100",
new Object[] {subid});
SubscriptionModel subscription = new SubscriptionModel();
System.out.println("bbox");
SqlRowSetMetaData rsmd = rows.getMetaData();
type = new String[rsmd.getColumnCount()];
for(int col=0;col<rsmd.getColumnCount();col++)
type[col] = rsmd.getColumnTypeName(col + 1);
System.out.println("Read rows and only serial clob data type values");
while(rows.next()){
System.out.println("test 1 here");
for(int col=0;col<rsmd.getColumnCount();col++){
System.out.println("test 2 here");
if("CLOB".equals(type[col]){
System.out.println("test 3 here");
SerialClob clob = (SerialClob) ((ResultSet) rows).getClob(col + 1);
if(clob != null){
System.out.println("clob is not null");
Reader is = clob.getCharacterStream();
sb = new StringBuffer();
length = (int) clob.length();
if(length>0){
buffer = new char[length];
count = 0;
try{
while((count = is.read(buffer)) != -1)
sb.append(buffer);
data = new String(sb);
}catch(Exception e){
}
}
else
data = (String) null;
}else
data = (String) null;
}else{
data = (String) rows.getObject(col + 1);
}
}
}
return subscription;
}catch(Exception e){
e.printStackTrace();
}
But I am getting an error like:
bbox
Read rows and only serial clob data type values
test 1 here
test 2 here
java.lang.ClassCastException: javax.sql.rowset.serial.SerialClob cannot be cast to java.lang.String
Where is my mistake?

Well this is at least one problem:
if(type[col] == "CLOB")
That's comparing string references directly. I suspect this would work better:
if ("CLOB".equals(type[col]))
That will get you into the right if block. I haven't looked in detail at the rest of your code - it would be simpler to read and maintain if you could break it up into smaller methods.

The problem is most likely here --
if(type[col] == "CLOB"){ // <-- This does Object equality
Use String#equals() method to do String comparisons.
if ( "CLOB".equals(type[col]) ) {