Hi while developing one of my web application i am storing the user information in to an ArrayList based on sql query executed, it contain duplicate objects how to remove duplicate objects in list , i already tried some method but it still not working.
This Is My Code Correct me where i am wrong
public ArrayList loadData() throws ClassNotFoundException, SQLException {
ArrayList userList = new ArrayList();
String url = "";
String dbName = "";
String userName = "";
String password = "";
Connection con = null;
Class.forName("org.apache.derby.jdbc.ClientDriver");
con = DriverManager.getConnection(url + dbName, userName, password);
PreparedStatement ps = null;
try {
String name;
String fatherName;
int Id;
String filePath;
int age;
String address;
String query = "SELECT NAME,FATHERNAME,AGE,ADDRESS,ID,FILEPATH FROM USER_INFORMATION ,USER_PHOTO WHERE ID=USER_ID";
ps = con.prepareStatement(query);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
name = rs.getString(1);
fatherName = rs.getString(2);
age = rs.getInt(3);
address = rs.getString(4);
Id = rs.getInt(5);
filePath=rs.getString(6);
/* if(flag)
{
prev=Id;
flag=false;
}
else if(Id==prev)
{
TEMP=TEMP+";"+filePath;
}*/
//PhotoList = PhotoList(Id, con);
UserData list = new UserData();
list.setName(name);
list.setFatherName(fatherName);
list.setAge(age);
list.setAddress(address);
list.setId(Id);
// list.setFilePath(filePath);
userList.add(list);
}
ps.close();
con.close();
} catch (Exception e) {
e.printStackTrace();
}
ArrayList al = new ArrayList();
HashSet hs = new HashSet();
hs.addAll(userList);
al.clear();
al.addAll(hs);
return al;
}
And My Bean Class contant is
public class UserData {
private String name;
private String fatherName;
private int Id;
//private String filePath;
private int age;
private String address;
public UserData()
{
}
public UserData(String name, String fatherName,int Id, int age,String address)
{
this.name = name;
this.fatherName = fatherName;
this.Id = Id;
//this.filePath=filePath;
this.age=age;
this.address=address;
}
//GETTER AND SETTER..
General Idea: Use Set, not List. But you must override hash and equals of the class.
If you want a Collection of objects that does not have a specific order and you don't want duplicates, it's better for you just to use a Set like for example HashSet, or, if in your set the order is important, the TreeSet.
Just remember to override the hash and equals methods.
if you add this to your bean everything should work:
public int hashCode() {
return (name + fatherName+ Id + filePath + age + address).hashCode();
}
public boolean equals(Object obj) {
return ( hashCode() == obj.hashCode() );
}
Your userdata class does not implement equals or hashcode. This means two instances created with the same values will not be counted as duplicates. This is why the set contains duplicates.
For example
UserData u1 = new UserData("Foo", "bar",1, 1,"baz");
UserData u2 = new UserData("Foo", "bar",1, 1,"baz");
u1 and u2 are not considered equal as they are different objects. Adding an equals and hashcode method should fix this. However even better is adarshr's idea of removing dupes in the SQL.
All duplicates must be removed at an SQL level. Your SQL is suggesting that it could be generating duplicate records.
String query = "SELECT NAME,FATHERNAME,AGE,ADDRESS,ID,FILEPATH FROM USER_INFORMATION ,USER_PHOTO WHERE ID=USER_ID";
What does the clause ID = USER_ID mean? Shouldn't you be passing in that value as an input to your query?
Also, is the column ID a primary key? Otherwise, use a where clause that doesn't generate duplicates.
Related
there is table of employee in database like in this image and use jdbc and java to fetch data from table. expected result also in image.
desired output in image
You can create an Employee class which contains the list of reports as below along with empId and reportingId:
public class Employee {
private String empId;
private String reportingId;
private List<Employee> reports;
public Employee(String empId, String reportingId) {
this.empId = empId;
this.reportingId = reportingId;
this.reports = new ArrayList<>();
}
public String getEmpId() {
return empId;
}
public String getReportingId() {
return reportingId;
}
public List<Employee> getReports() {
return reports;
}
}
// Step 1: Connect to the database
Connection conn = DriverManager.getConnection(connectionString, username, password);
// Step 2: Execute a SELECT statement
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT empId, reportingId FROM employee");
// Step 3: Iterate over the resultset and create a Map of Employee objects
Map<String, Employee> employees = new HashMap<>();
while (rs.next()) {
String empId = rs.getString("empId");
String reportingId = rs.getString("reportingId");
Employee employee = new Employee(empId, reportingId);
employees.put(empId, employee);
}
// Step 4: Iterate over the Map and create the hierarchy of Employee objects
for (Employee employee : employees.values()) {
Employee manager = employees.get(employee.getReportingId());
if (manager != null) {
manager.getReports().add(employee);
}
}
// The hierarchy of Employee objects is now complete
You can then print the hierarchy of Employee objects using a recursive method, like this:
public void printHierarchy(Employee employee, int level) {
for (int i = 0; i < level; i++) {
System.out.print("\t");
}
System.out.println(employee.getEmpId());
for (Employee report : employee.getReports()) {
printHierarchy(report, level + 1);
}
}
Call the printHierarchy method from 101 employee
Output:
101
1013
1012
101222
101223
1011
101101
101102
My information is read in via CSV for "banking information", A person CSV is
5
1,Tony,Stark,C,tonys,naslvj34-t934,stark#hmmm.org;tony#gmail.com;tostark55#yaho.com
2,Patrick,Hart,C,phart2,sdlwgl5034i52,hart#hmmm.org;hart1#who.org
3,Tom,Baker,E,bake95,kweojtnefq567,
4,Kevin,Black,C,keb765,prjhohier99,black#mail.org
5,Alex,Codd,E,alcodd,andlqjr78,codd#DBMS.org;alex#gmail.com
my Account CSV is,
5
1,313001,S,35881.12
2,313002,G,772400.34
3,313003,C,250002.15
4,313004,P,96310.66
5,313005,P,15624.15
1,313006,C,39950.99
In the Account CSV the 2nd token is My "Account type", so S = "Savings" G = "Gold Savings" C = "Checkings" and so on. When reading these in my CSV parser class, an object was made of the types, so A Checking class was made and when the CSV was tokenized when token[2] was equal to "C".
My Persons class is set up as so, excluding my getters and setters
private int personId;
private String firstName;
private String lastName;
private String type;
private String usrname;
private String password;
private ArrayList<String> emails;
public Person(int personId, String firstName, String lastName, String type, String usrname, String password,
ArrayList<String> emails) {
super();
And my Account class is set up as so.
private Person accountHolder;
private int accountNumber;
private double currentBalance;
public Account() {}
public Account(Person accountHolder, int accountNumber, double currentBalance) {
this.accountHolder = accountHolder;
this.accountNumber = accountNumber;
this.currentBalance = currentBalance;
}
This is one of my example account types (there are multiple)
public class CheckingAccount extends Account {
public CheckingAccount(Person p, int i, double d) {
super(p,i, d);
}
This is my database adder
public static void DbAddAccount(Person personId, Account accountHolder){
Connection conn = null;
try {
conn = DriverManager.getConnection(DatabaseInfo.URL, DatabaseInfo.USERNAME, DatabaseInfo.PASSWORD);
} catch (SQLException e) {
System.out.println("Connection Failed");
throw new RuntimeException(e);
}
String accountQuery = "insert into Account (accountId,accountNumber,currentBalance,type,personId) values (?,?,?,?,?);";
PreparedStatement accountPs = null;
ResultSet accountKeys = null;
int accountId = 0;
try {
//These are my prepare Statements for my queries
accountPs = conn.prepareStatement(accountQuery);
accountPs.setInt(1, accountId+ 1 );
accountPs.setInt(2, accountHolder.getAccountNumber());
accountPs.setDouble(3, accountHolder.getCurrentBalance());
accountPs.setString(4, ??????????????????????????????????);
accountPs.setInt(5, personId.getPersonId());
accountPs.executeUpdate();
accountPs.close();
conn.close();
}
catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
JDBC is not adding anything when running.
I think your code has following issues:
Account Object:
Object is missing field to store "Account Type"
Setting incorrect account type in DbAddAccount method
At line accountPs.setString(4, ??????????????????????????????????);
you are number of question marks (without enclosing in quote to make string) as account type which appears it is not correct.
series of ??? wont get converted to string without enclosed in quotes.
Even if you enclose in quotes, I think it wont be intended account number;
Solution
for Issue 1; declare account_type in Account Object.
for issue 2; instead of using accountPs.setString(4, ??????????????????????????????????);
use:
accountPs.setString(4, account.getAccountType());
I am using Spring MVC with JdbcTemplate and a MySQL database.
Say I have the following 2 tables :
table_school
ID NAME
table_students
ID NAME ADDRESS SCHOOL_ID
I have a School POJO that has the following class variables :
int id, String name, List<Student> students
Is there a way of retrieving a List with each School object containing the appropriate List of Student objects using JdbcTemplate in one query? I know this is easily achievable using Hibernate but I would like to use JdbcTemplate ..
Many thanks !
Yes, you can fetch all data in 1 query.
Simple example:
class Student {
int id;
String name;
String addr;
Student(int id, String name, String addr) {
this.addr = addr;
this.id = id;
this.name = name;
}
}
class School {
int id;
String name;
List<Student> students = new ArrayList<>();
School(int id, String name) {
this.id = id;
this.name = name;
}
void addStudent(Student s) {
students.add(s);
}
}
/*
* helper method that gets school from map or create if not present
*/
private School getSchool(Map<Integer, School> schoolMap, int id, String name) {
School school = schoolMap.get(id);
if (school == null) {
school = new School(id, name);
schoolMap.put(id, school);
}
return school;
}
// RUN QUERY
String sql =
" select st.ID, st.NAME, st.ADDRESS. s.id, s.name" +
" from table_students st" +
" inner join table_school s on st.school_id = s.id";
final Map<Integer, School> schoolMap = new HashMap<>();
jdbcTemplate.query(sql, new RowCallbackHandler() {
#Override
public void processRow(ResultSet rs) throws SQLException {
int studentId = rs.getInt(1);
String studentName = rs.getString(2);
String studentAddr = rs.getString(3);
int schoolId = rs.getInt(4);
String schoolName = rs.getString(5);
Student student = new Student(studentId, studentName, studentAddr);
getSchool(schoolMap, schoolId, schoolName).addStudent(student);
}
});
One final point regarding fetching performance:
If you expect many records to fetch it is nearly always a good idea to increase jdbc fetch size parameter. So before run query set it on your jdbcTemplate:
jdbcTemplate.setFetchSize(200); // you can experiment with this value
or if you are using spring's JdbcDaoSupport you can use such pattern:
public class MyDao extends JdbcDaoSupport {
....
#Override
protected void initTemplateConfig() {
getJdbcTemplate().setFetchSize(200);
}
}
I'm making a mysql database connector with java to show all the data.
When I run the code, I get an NullPointerException in my getData() function.
here is my code.
public String[][] getData() {
String values[][];
try {
rs = st.executeQuery("SELECT * FROM adresses");
int i = 0;
while(rs.next()) {
String id = rs.getString("id");
String name = rs.getString("name");
String adress = rs.getString("email_adress");
String catagory = rs.getString("catarogy");
values[i][0] = id;
values[i][1] = name;
values[i][2] = adress;
values[i][3] = catagory;
i++;
}
return values;
} catch (SQLException e) {
e.printStackTrace();
return values;
}
}
When the value of the String values is nothing I get The error. But if I give the String allready a value it says nothing .
public String[][] getData() {
String values[][] = {{"","","",""},
{"","","",""},
{"","","",""},};
try {
rs = st.executeQuery("SELECT * FROM adresses");
int i = 0;
while(rs.next()) {
String id = rs.getString("id");
String name = rs.getString("name");
String adress = rs.getString("email_adress");
String catagory = rs.getString("catarogy");
values[i][0] = id;
values[i][1] = name;
values[i][2] = adress;
values[i][3] = catagory;
i++;
}
return values;
} catch (SQLException e) {
e.printStackTrace();
return values;
}
}
I want more data than that in my data String. how can I let it automatically do that??
Tnx.
PS.
The function is called in my class FrameGUI and has to change to Object
public class FrameGUI extends JFrame {
public JTable dataHolder;
Mysql mysql = new Mysql();
public String[] columnNames = {
"ID", "Name", "Adress", "Catagory"
};
-> public Object[][] data = mysql.getData();
public FrameGUI() {
init();
mysql.getData();
}
}
You do not initialize String values[][] so it is null. You either need to initialize it first or use a more appropriate datastructure like a List.
You should define a class and use a List (e.g. the ArrayList) instead.
e.g. if you want to call it User -
public class User {
private String id;
private String name;
//...
}
and a list
List<User> users = new ArrayList<User>();
and then instantiate the User class for each row and add the new instance to the list -
User currUser = new User();
users.add(currUser);
//set values from result set
The list can grow automatically when needed and the code is much more readable than using the array.
You get an index out of bounds in the first example because a String[][] (or String Matrix) gets initialized as a zero-length array.
In the second instance, you initialized the array to a size of 3x4 - that works so long as you only get 3 results back.
What you really need is a data structure with a dynamic size. Arrays aren't automatically sized dynamically. Try using a collection implementation like ArrayList or LinkedList or Vector.
Also, instead of saving your values to a String[], try creating a bean class that can hold your result. Create a new instance of it for each result that you get back instead of initializing a new array.
Because you didn't initialized your array, that is why you get NPE. Actually I suggest you to use List for your purposes:
public ArrayList<ArrayList<String>> getData() {
ArrayList<ArrayList<String>> values = new ArrayList<>();
try {
rs = st.executeQuery("SELECT * FROM adresses");
while(rs.next()) {
String id = rs.getString("id");
String name = rs.getString("name");
String adress = rs.getString("email_adress");
String catagory = rs.getString("catarogy");
ArrayList<String> list = new ArrayList<>();
list.add(id);
list.add(name);
list.add(adress);
list.add(catagory);
values.add(list);
}
return values;
} catch (SQLException e) {
e.printStackTrace();
return null;
}
}
The main problem in you code is you are using arrays to save variable number of data. Arrays is fixed sized after they are created so you can't add (or remove) elements to them dynamically.
Instead of using arrays you should use an ArrayList object which have methods to add more elements. Also instead of creating a multidimensional array it looks like a better idea to create a class for the data you get from you database.
So lets first create a Address class:
public class Address {
public String id, name, adress, catagory;
public Address(String id, String name, String adress, String catagory) {
this.id = id;
this.name = name;
this.adress = adress;
this.catagory = catagory;
}
}
Now you can write you code as:
public List<Address> getData() {
List<Address> values = new ArrayList<Address>();
try {
rs = st.executeQuery("SELECT * FROM adresses");
int i = 0;
while(rs.next()) {
String id = rs.getString("id");
String name = rs.getString("name");
String adress = rs.getString("email_adress");
String catagory = rs.getString("catarogy");
values.add(new Address(id, name, adress, catagory));
}
return values;
} catch (SQLException e) {
e.printStackTrace();
return values;
}
}
The returned list will contain a list of Address objects which have the values from you database. Also, the size of the list is always the same as the content you put into it.
I have a database server communicating with a Java application server using JDBC. I want to store data from the database ResultSet into Java variables.
Here's my Java class, HRPeople:
public class HRPeople {
public int elements;
public String[] FirstName;
public String[] LastName;
public String[] Email;
public int[] Salary;
}
I currently use this class to store data from ResultSet, as follows:
query = "SELECT first_name, last_name, email, salary FROM HR.Employees where rownum < 6";
rset = stmt.executeQuery(query);
while (rset.next()) {
returnHRdata.FirstName[ii] = rset.getString("first_name");
returnHRdata.LastName[ii] = rset.getString("last_name");
returnHRdata.Email[ii] = rset.getString("email");
returnHRdata.Salary[ii] = rset.getInt("salary");
ii = ii + 1;
}
The problem with the above scenario is that the primitive arrays require me to know the number of rows in the ResultSet so that I can properly initialize those arrays. So what I want to do is use an ArrayList instead. How would I modify the above scenario to do this?
Here's my initial attempt (is this close)? Is HRPeople.java file shown above even used in this scenario?
query = "SELECT first_name, last_name, email, salary FROM HR.Employees where rownum < 6";
rset = stmt.executeQuery(query);
List<HRPeople> returnHRdata = new ArrayList<HRPeople>();
while (rset.next()) {
returnHRdata.FirstName = rset.getString("first_name");
returnHRdata.LastName = rset.getString("last_name");
returnHRdata.Email = rset.getString("email");
returnHRdata.Salary = rset.getInt("salary");
returnHRdata.add;
}
UPDATE 1:
If I add to the code the following,
return returnHRdata;
I get the following error (any idea why?):
myClass.java:213: incompatible types
found : java.util.List<HRPerson>
required: java.util.ArrayList<HRPerson>
return returnHRdata;
^
1 error
You probably want to first define an HRPerson like this:
public class HRPerson {
public String firstName;
public String lastName;
public String email;
public int salary;
}
Then your main code would look like:
query = "SELECT first_name, last_name, email, salary FROM HR.Employees where rownum < 6";
rset = stmt.executeQuery(query);
List<HRPerson> returnHRdata = new ArrayList<HRPerson>();
while (rset.next()) {
HRPerson person = new HRPerson();
person.firstName = rset.getString("first_name");
person.lastName = rset.getString("last_name");
person.email = rset.getString("email");
person.salary = rset.getInt("salary");
returnHRdata.add(person);
}
List<HRPeople> returnHRdata = new ArrayList<HRPeople>();
while (rset.next()) {
HRPeople people = new HRPeople();
people.FirstName = rset.getString("first_name");
people.LastName = rset.getString("last_name");
people.Email = rset.getString("email");
people.Salary = rset.getInt("salary");
returnHRdata.add(people);
}
You can improve this code by using a lowerCase letter for your first char of your fields and using getters and setters to access them.
Convert this:
public class HRPeople {
public int elements;
public String[] FirstName;
public String[] LastName;
public String[] Email;
public int[] Salary;
}
to:
public class HRPerson {
public String firstName;
public String lastName;
public String email;
public int salary;
}
and:
List<HRPerson> people = new ArrayList<HRPerson>();
Now it should be easy:
while (rset.next()) {
HRPerson person = new HRPerson();
returnHRdata.firstName = rset.getString("first_name");
returnHRdata.lastName = rset.getString("last_name");
returnHRdata.email = rset.getString("email");
returnHRdata.salary = rset.getInt("salary");
people.add(person);
}
Close...
while (rset.next()) {
HRPeople person = new HRPeople();
person.setFirstName(rset.getString("first_name"));
person.setLastName(rset.getString("last_name"));
person.setEmail(rset.getString("email"));
person.setSalary(rset.getInt("salary"));
returnHRdata.add(person);
}
You of course must define the setXXXX methods on the HRPerson class. Oh yeah, and do what Thomasz suggested.
create a class HRPeople, which has firstname, lastname.... attributes, and declare getter, setters method.
then:
List<HRPeople> returnHRdata = new ArrayList<HRPeople>();
HRPeople people = null;
while (rset.next()) {
people = new HRPeople();
people.setFirstName( rset.getString("first_name"));
people.setLastName (rset.getString("last_name"));
...
returnHRdata.add(people);
}
Instead of storing an array of each property in your object, make a single object to describe a given entity in the table.
class HRPerson {
String firstName;
String lastName;
String email;
Integer salary;
}
Create a list of this type, allowing you to store the results.
List<HRPerson> hrPeople = new ArrayList<HRPerson>();
while(rset.next()) {
HRPerson person = new HRPerson();
person.firstName = rset.getString("first_name");
person.lastName = rset.getString("last_name");
person.email = rset.getString("email");
person.salary = rset.getInt("salary");
hrPeople.add(person);
}
Finally, fill it by creating new objects for each row in your table.