public class Database {
private String ric;
private String volume;
private String _url;
private String _userId;
private String _password;
private String _dbLib;
private String _dbFile;
private Connection _conn;
private PreparedStatement _statement;
public Database(LSE item) {
ric = item.get_ric();
volume = item.get_volume();
}
public void writeToDb() throws SQLException{
//setString
}
}
I have a ItemDispatcher class:
public class ItemDispatcher implements Runnable {
private LSE lse;
public ItemDispatcher(LSE lseItem) {
this.lse= lseItem;
}
#Override
public void run() {
try {
new Database(lse).writeToFile();
} catch (IOException e) {
e.printStackTrace();
}
}
}
run() method in ItemDispatcher runs repeatedly. I want to create database connection and prepareStatement in Database class, but doing this on Database class constuctor would create connection many times over. How can I change my design to create connection just once and not over and over again on every execution of run(). I am trying to not do this in any other class and just Database class
Within the scope of ItemDispatcher, declare private variable X of type Database. You might initialize it in a separate method (best) or in the constructor (might be ok). Use the private variable X instead of creating a new instance in method run
Do it in a static block in class Database
static {
}
But this implies that Connections and Statement will be static and then shared by all instances of Database.
Just as an example from another SO post:
public static final Map<String, String> initials = new HashMap<String, String>();
static {
initials.put("AEN", "Alfred E. Newman");
// etc.
}
Use the Singleton pattern . This will allow you to have only one instace of the Database connection.
Taking your code as an example, it would be like this :
public class Database {
private String ric;
private String volume;
private String _url;
private String _userId;
private String _password;
private String _dbLib;
private String _dbFile;
private Connection _conn;
private PreparedStatement _statement;
private static final Database INSTANCE;
private Database(LSE item) {
ric = item.get_ric();
volume = item.get_volume();
}
public static final Database getInstance(LSE item) {
if (INSTANCE == null) {
INSTANCE = new Database(LSE item);
}
return INSTANCE;
}
public void writeToDb() throws SQLException{
//setString
}
}
If your application will be using Threads (Concurrency), I suggest you also to prepare your singleton for those situations , see this question
Related
My PoIs class:
public class PoIs {
private Integer location_id;
private String location_name;
private String location_address;
public PoIs() {}
public PoIs(Integer location_id, String location_name, String location_address) {
this();
this.location_id = location_id;
this.category_id = category_id;
this.location_name = location_name;
this.location_address = location_address;
}
public Integer get_location_id() {
return location_id;
}
public void set_location_id(Integer location_id) {
this.location_id = location_id;
}
public String get_location_name() {
return location_name;
}
public void set_location_name(String location_name) {
this.location_name = location_name;
}
public String get_location_address() {
return location_address;
}
public void set_location_address(String location_address) {
this.location_address = location_address;
}
I populate PoIs with informatision from a sqlite database:
final PoIs p = new PoIs(Integer.parseInt(row.get(0).toString()), row.get(1).toString(), row.get(2).toString());
and at a moment intend to save them on a firabase database:
FIREBASE_REFERENCE.child("PoI_"+ p.get_location_id()).setValue(p)
.addOnCompleteListener(t -> {
final boolean isSuccessful = t.isSuccessful();
final String msg = !isSuccessful
? getResources().getString(R.string.fb_error)
: getResources().getString(R.string.fb_success);
});
All work perfect except that my firebase fields start with an underscore. Instead location_id, location_name, location_address I have _location_id, _location_name, _location_address. I can't understand why this happening. Any ideea how to resolve this issue?
Firebase uses JavaBean naming conventions when mapping from properties in your code to properties in the database. In that convention a method like get_location_name is the getter for a property called _location_name.
If you want the property in the database to be location_name, that'd be a getter getLocation_name. Alternatively, you can use a #PropertyName("location_name")) annotation on all accessors (so the getter/setter function and/or the public field) to indicate the explicit property name you want in the database.
I am implementing a component where one component receive a message, it sends another message to Audit component so it can be audited.
Audit handler has model called AuditObject, and my component has MessageObject. Here is the code:
public final class AuditObject {
private final Long id;
private final String studyUid;
private final AuditPatient patient;
...
}
public final class MessageObject {
private final Long id;
private final String studyUid;
private final PatientObject patient;
private final String accessorName;
...
}
AuditPatient and PatientObject have same variables.
I am trying to send it through amqp connection via jms message. I already have MessageGateway. So my code will look like this on my side.
public void send(MessageObject messageObject) {
//translate MessageObject to AuditObject
messageGateway.send(auditObject, endpoint);
}
What is the best way to translate(or map) MessageObject to AuditObject? Do I have to manually create each fields by assigning them? What is the best way to approach this problem?
Use static method in a class to convert one object to another and call it.
class ConvertObject {
public static AuditObject convertMessageObjectToAudioObject(MessageObject messageObject) {
AuditObject auditObject = new AuditObject();
auditObject.setStudyUid(messageObject.getStudyUid());
auditObject.setPatient(messageObject.getPatient());
return auditObject;
}
}
public void send(MessageObject messageObject) {
AuditObject auditObject = ConvertObject.convertMessageObjectToAudioObject(messageObject);
messageGateway.send(auditObject, endpoint);
}
I have a couple of objects from which selected members should be combined to create an output object. All these are POJOs. I am seeing that all object mappers work on a single POJO to another POJO level. Is there any mapper that supports what I am looking for? Of course, I understand that there is some mapping stuff that I need to specify.
Edit:
I know how to get this done by writings own Java class. I am just looking for a way to do it with one of the mapping libraries.
You aren't limited in what you require to be passed to your mapper. You can define it to accept several items and build the object based on the multiple inputs. Here is an example:
public class ClassOne {
private final String someProperty;
public ClassOne(String someProperty) {
this.someProperty = someProperty;
}
public String getSomeProperty() {
return someProperty;
}
}
public class ClassTwo {
private final String someOtherProperty;
public ClassTwo(String someOtherProperty) {
this.someOtherProperty = someOtherProperty;
}
public String getSomeOtherProperty() {
return someOtherProperty;
}
}
public class CombinedClass {
public static CombinedClass mapper(ClassOne one, ClassTwo two){
return new CombinedClass(one.getSomeProperty(), two.getSomeOtherProperty());
}
private final String someProperty;
private final String someOtherProperty;
private CombinedClass(String someProperty, String someOtherProperty) {
this.someProperty = someProperty;
this.someOtherProperty = someOtherProperty;
}
public String getSomeProperty() {
return someProperty;
}
public String getSomeOtherProperty() {
return someOtherProperty;
}
}
I have a HashMap that look something like this-
HashMap<String, TableConnectionInfo> tableList
which means it's value is a Class TableConnectionInfo which looks something like this-
public class TableConnectionInfo {
public String url;
public String user;
public String password;
public String driver;
public String suffix;
public String sql;
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getUser() {
return user;
}
public void setUser(String user) {
this.user = user;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getDriver() {
return driver;
}
public void setDriver(String driver) {
this.driver = driver;
}
public String getSuffix() {
return suffix;
}
public void setSuffix(String suffix) {
this.suffix = suffix;
}
public String getSql() {
return sql;
}
public void setSql(String sql) {
this.sql = sql;
}
}
So Suppose, If I have two values in the above HashMap. That means, I need to make two different connections to two different database. And suppose if that map has three values, then I need to make three different connections to three different database.
In the main thread, I am populating the above map by reading it from the properties file like this and after that this map won't get modified.
for (String arg : databaseNames) {
TableConnectionInfo ci = new TableConnectionInfo();
String url = prop.getProperty(arg + ".url");
String user = prop.getProperty(arg + ".user");
String password = prop.getProperty(arg + ".password");
String driver = prop.getProperty(arg + ".driver");
String suffix = prop.getProperty(arg + ".suffix");
String sql = prop.getProperty(arg + ".sql");
ci.setUrl(url);
ci.setDriver(driver);
ci.setPassword(password);
ci.setSql(sql);
ci.setSuffix(suffix);
ci.setUser(user);
tableList.put(arg, ci);
}
Now I am passing this tableList map to various threads like this and it won't be modified (by making set calls) by any thread. Each thread will be using get method to get the required method.
for (int i = 0; i< 1000; i++) {
service.submit(new Task(tableList));
}
So in the run method I need to make different conenctions basis on the tableList size. So if tableList size is two, that means I need to make two different connections, callableStatements and methods to two different database.
Question:-
So is there any better way as compared to way I am doing in my run method to create different connections to database basis on tableList size ?
Below is my Task class that impelements Runnable Interface
class Task implements Runnable {
private Connection[] dbConnection = null;
private CallableStatement[] callableStatement = null;
private ArrayList<Method> methods[] = null;
private final HashMap<String, TableConnectionInfo> tableLists;
public Task(HashMap<String, TableConnectionInfo> tableList) {
this.tableLists = tableList;
}
#Override
public void run() {
try {
int j = 0;
dbConnection = new Connection[tableLists.size()];
callableStatement = new CallableStatement[tableLists.size()];
methods = new ArrayList[tableLists.size()];
for (TableConnectionInfo ci : tableLists.values()) {
dbConnection[j] = getDBConnection(ci.getUrl(), ci.getUser(), ci.getPassword(), ci.getDriver());
callableStatement[j] = dbConnection[j].prepareCall(ci.getSql());
methods[j] = getRequiredMethods(ci.getSuffix());
j++;
}
}
}
}
Make a connection to that database-
private Connection getDBConnection(String url, String username, String password, String driver) {
Connection dbConnection = null;
try {
Class.forName(driver);
dbConnection = DriverManager.getConnection(url, username, password);
}
return dbConnection;
}
Just to add here getRequiredMethods will get all the methodNames of a particular table. So suppose if tableList size is 1 then we will be having only one connection to that database so getRequiredMethods will get all the methods for that table1 and store it in a ArrayList. But suppose if tableList size is 2 then we will be having two different connections to two different database so that is the reason I made methods as an array so that it can hold methods for table 1 and methods for table 2.
Ok, I'm still not sure how the Task is meant to use the data it's getting. But, I would move the getConnection, getCallableStatement and getMethods() functions to methods on the TableConnectionInfo. You can simply create a Collection of TableConnectionInfo (initialised as you already have, storing in an ArrayList). Then the Runnable simply iterates through the TableConnectionInfo.
public class TableConnectionInfo {
private String url;
private String user;
private String password;
private String driver;
private String suffix;
private String sql;
private Connection connection;
<snip... getters and setters for the properties>
public Connection getConnection() {
// TODO create and return a connection
if (connection == null) {
// create the connection
}
return connection;
}
public CallableStatement getCallableStatement() {
// get the callable statement
return null;
}
public Collection<Method> getMethods() {
// Get the Methods
return null;
}
}
public class TableTask implements Runnable {
private Collection<TableConnectionInfo> tables;
public TableTask(Collection<TableConnectionInfo> tables) {
this.tables = tables;
}
#Override
public void run() {
for (TableConnectionInfo table : tables) {
// do something with table.getConnection(), or table.getCallableStatement()
// and/or table.getMethods()
}
}
}
I'm new in java programming and trying to learn it.
I ran into a problem that cannot find a solution for it in the web:
I have an enum, that is a "list" of actions and each of them has a property
of type Actions that conains a list of possible subactions. The subacions are constant string.
I'd like to instanziate a anonymus instance of Actions in the enum constructor so that
in addition to the standart subactions, each enum could have its subactions
I tried to write an enum like the following
public enum Action {
ACTION1("One", new Actions(){
public static final String TEST = "test";
}),
ACTION2("TWO", null),
ACTION3("THREE,null);
private final String act;
public final Actions actions;
private Action(String act, Actions actions) {
this.act = act;
this.actions = actions;
}
}
and this is Actions class
public class Actions {
public static final String SUBACTION_TEST1 = "suoOne";
public static final String SUBACTION_TEST2 = "subTwo";
}
than, this is how I use the Action enum:
String as = Action.ACTION1.params.SUBACTION_TEST1;
and up to here it wors but I'cannot write this:
String ast = Action.ACTION1.params.TEST;
I know that probably this approach is wrong but before the change the implementation
I'd like to know why doesn't work.
Thanks.
Your enum has no property named params, which is the immediate reason your code example does not work. One thing you could do to improve this design, is to have your Actions class return the list of sub-actions via a well defined method:
public class Actions {
public static final String SUBACTION_TEST1 = "suoOne";
public static final String SUBACTION_TEST2 = "subTwo";
public List<String> getSubActions() {
return Arrays.asList(SUBACTION_TEST1, SUBACTION_TEST2);
}
}
public enum Action {
ACTION1("One", new Actions(){
public static final String TEST = "test";
#Override
public List<String> getSubActions() {
return Arrays.asList(TEST);
}
}),
private final String act;
private final Actions actions;
private Action(String act, Actions actions) {
this.act = act;
this.actions = actions;
}
public Actions getActions() {
return actions;
}
}
And to use this:
List<String> subActionList = Action.ACTION1.getSubActions();