Operations
XAP provides a simple space API using the GigaSpace interface for interacting with the space.
The interface includes the following main operations:
write one object into the space
writeMultiple objects into the Space
asynchronous write to the Space
change one object in Space
changeMultiple objects in Space
asynchronous change of objects
readById from the Space
readByIds from the Space
read object by template from the Space
readMultiple objects from the Space
read asynchronous from the Space
read if exists
read if exists by id
take object by template from Space
takeById object by id from Space
takeByIds objects by ids from Space
takeMultiple objects from Space
take asynchronous
take if exists
clear objects in Space
aggregation across the Space
count objects in Space
counters increment and decrement
Simpler API
The GigaSpace
interface provides a simpler space API by utilizing Java 5 generics, and allowing sensible defaults. Here are some examples of the space operations as defined within GigaSpace
:
public interface GigaSpace {
<T> LeaseContext<T> write(T entry) throws DataAccessException;
// ....
<T> T read(ISpaceQuery<T> query, Object id)throws DataAccessException;
// ......
<T> T take(T template) throws DataAccessException;
<T> T take(T template, long timeout) throws DataAccessException;
// ......
}
In the example above, the take operation can be performed without specifying a timeout. The default take timeout is 0
(no wait), and can be overridden when configuring the GigaSpace
factory. In a similar manner, the read timeout and write lease can be specified.
The Write Operation
In order to write objects to the Space, you use the write method of the GigaSpace interface. The write method is used to write objects if these are introduced for the first time, or update them if these already exist in the space. In order to override these default semantics, you can use the overloaded write methods which accept update modifiers such as WriteModifiers.UPDATE_ONLY.
POJO Example
The following example writes an Employee
object into the space:
GigaSpace space = ....
Employee employee = new Employee("Last Name", new Integer(32));
employee.setFirstName("first name");
LeaseContext<Employee> lc = space.write(employee);
SpaceDocument Example
Here is an example how you create a SpaceDocument, register it with the space and then write it into the space:
// Create the document
DocumentProperties properties = new DocumentProperties()
.setProperty("CatalogNumber", "av-9876")
.setProperty("Category", "Aviation")
.setProperty("Name", "Jet Propelled Pogo Stick")
.setProperty("Price", 19.99f)
.setProperty("Tags",
new String[] { "New", "Cool", "Pogo", "Jet" })
.setProperty("Features",
new DocumentProperties()
.setProperty("Manufacturer", "Acme")
.setProperty("RequiresAssembly", true)
.setProperty("NumberOfParts", 42));
SpaceDocument doc = new SpaceDocument("Product", properties);
// Register the document
// Create type descriptor:
SpaceTypeDescriptor typeDescriptor = new SpaceTypeDescriptorBuilder(
"Product").idProperty("CatalogNumber")
.routingProperty("Category")
.addPropertyIndex("Name", SpaceIndexType.BASIC)
.addPropertyIndex("Price", SpaceIndexType.EXTENDED).create();
// Register type:
space.getTypeManager().registerTypeDescriptor(typeDescriptor);
// Write the document into the space
LeaseContext<SpaceDocument> lc = space.write(document);
Time To Live
To write an object into the space with a limited time to live you should specify a lease value (in millisecond). The object will expire automatically from the space.
gigaSpace.write(myObject, 10000)
Write Multiple
When writing a batch of objects into the space, these should be placed into an array to be used by the GigaSpace.writeMultiple
operation. The returned array will include the corresponding LeaseContext
object.
Example
Employee emps[] = new Employee[2];
emps[0] = new Employee("Last Name A", new Integer(10));
emps[1] = new Employee("Last Name B", new Integer(20));
try {
LeaseContext[] leaseContexts = space.writeMultiple(emps);
for (int i = 0;i<leaseContexts.length ; i++) {
System.out.println ("Object UID " + leaseContexts[i].getUID() + " inserted into the space");
}
} catch (WriteMultipleException e) {
IWriteResult[] writeResult = e.getResults();
for (int i = 0;i< writeResult.length ; i++) {
System.out.println ("Problem with Object UID " + writeResult ");
}
}
Here are a few important considerations when using the batch operation:
- should be performed with transactions - this allows the client to roll back the space to its initial state prior the operation was started, in case of a failure.
- make sure
null
values are not part of the passed array. you should verify that duplicated entries (with the same ID) do not appear as part of the passed array, since the identity of the object is determined based on its
ID
and not based on its reference. This is extremely important with an embedded space, sincewriteMultiple
injects the ID value into the object after the write operation (when autogenerate=false).Exception handling - the operation many throw the following Exceptions.
Return Previous Value
When updating an object which already exists in the space, in some scenarios it is useful to get the previous value of the object (before the update). This previous value is returned in result LeaseContext.getObject()
when using the RETURN_PREV_ON_UPDATE
modifier.
LeaseContext<MyData> lc = space.write(myobject,WriteModifiers.RETURN_PREV_ON_UPDATE.add(WriteModifiers.UPDATE_OR_WRITE));
MyData previousValue = lc.getObject();
Since in most scenarios the previous value is irrelevant, the default behavior is not to return it (i.e. LeaseContext.getObject()
return null). The RETURN_PREV_ON_UPDATE
modifier is used to indicate the previous value should be returned.
Asynchronous write
Asynchronous write
operation can be implemented using a Task, where the Task
implementation include a write operation. With this approach the Task
is sent to the space and executed in an asynchronous manner. The write operation itself will be completed once both the primary and the backup will acknowledge the operation. This activity will be performed as a background activity from the client perspective.
Example
GigaSpace space = new GigaSpaceConfigurer (new UrlSpaceConfigurer("jini://*/*/space")).gigaSpace();
MyClass obj = new MyClass(1,"AAA");
space.write(obj,WriteModifiers.ONE_WAY);
Modifiers
For further details on each of the available modifiers see: WriteModifiers
Writing an object into a space might generate notifications to registered objects.
Writes a new object to the space, returning its LeaseContext.
<T> LeaseContext<T> write(T entry) throws DataAccessException
<T> LeaseContext<T> write(T entry, long lease, long timeout, WriteModifiers modifiers) throws DataAccessException
......
Writes new objects to the space, returning its LeaseContexts.Java API
<T> LeaseContext<T>[] writeMultiple(T[] entries) throws DataAccessException
<T> LeaseContext<T>[] writeMultiple(T[] entries, long[] leases, WriteModifiers modifiers) throws DataAccessException
......
Modifier and Type | Description | default |
---|---|---|
T | POJO, SpaceDocument | |
lease | Time to live | Lease.FOREVER |
timeout | The timeout of an update operation, in milliseconds. If the entry is locked by another transaction wait for the specified number of milliseconds for it to be released. | 0 |
WriteModifiers | Provides modifiers to customize the behavior of write operations | UPDATE_OR_WRITE |
LeaseContext | LeaseContext is a return-value encapsulation of a write operation. |
The Change Operation
The GigaSpace.change and the ChangeSet allows updating existing objects in space, by specifying only the required change instead of passing the entire updated object. Thus reducing required network traffic between the client and the space, and the network traffic generated from replicating the changes between the space instances (e.g between the primary space instance and its backup).
Example:
The following example demonstrates how to update the property ‘firstName’ of an object of type ‘Person’ with id ‘myID’.
GigaSpace space = // ... obtain a space reference
String id = "myID";
IdQuery<WordCount> idQuery = new IdQuery<Person>(Person.class, id, routing);
space.change(idQuery, new ChangeSet().set("firstName", "John"));
The Read Operation
The read operations query the space for an object that matches the criteria provided. If a match is found, a copy of the matching object is returned. If no match is found, null is returned. Passing a null reference as the template will match any object.
Any matching object can be returned. Successive read requests with the same template may or may not return equivalent objects, even if no intervening modifications have been made to the space.
Each invocation of read
may return a new object even if the same object is matched in the space.
If you would like to read objects in the same order they have been written into the space you should perform the read objects in a FIFO mode.
The read
operation default timeout is JavaSpace.NO_WAIT
.
The read operation can be performed with the following options:
- Template matching
- By Id
- By IdQuery
- By SQLQuery
To learn more about the different options refer to Querying the Space
Examples:
The following example writes an Employee
object into the space and reads it back from the space :
Employee employee = new Employee("Last Name", new Integer(32));
employee.setFirstName("first name");
space.write(employee);
// Read by template
Employee template = new Employee(new Integer(32));
Employee e = space.read(template);
// Read by id
Employee e = space.readById(Employee.class, new Integer(32));
// Read by IdQuery
IdQuery<Employee> query = new IdQuery<Employee>(Employee.class,
new Integer(32));
Employee e = space.read(query);
// Read by SQLQuery
SQLQuery<Employee> query = new SQLQuery<Employee>(Employee.class,
"firstName='first name'");
Employee e = space.read(query);
Read multiple
The GigaSpace interface provides simple way to perform bulk read operations. You may read a large amount of objects in one call.
Examples:
Employee emps[] = new Employee[2];
emps[0] = new Employee("Last Name A", new Integer(31));
emps[1] = new Employee("Last Name B", new Integer(32));
space.writeMultiple(emps);
// Read multiple by template
Employee[] employees = space.readMultiple(new Employee());
// Read multiple by SQLQuery
SQLQuery<Employee> query = new SQLQuery<Employee>(Employee.class,"lastName ='Last Name B'");
Employee[] e = space.readMultiple(query);
// Read by Ids
Integer[] ids = new Integer[] { 31, 32 };
ReadByIdsResult<Employee> result = space.readByIds(Employee.class,ids);
Employee[] employees = result.getResultsArray();
// Read by IdsQuery
Integer[] ids = new Integer[] { 31, 32 };
IdsQuery<Employee> query = new IdsQuery<Employee>(Employee.class, ids);
ReadByIdsResult<Employee> result = space.readByIds(query);
Employee[] employees = result.getResultsArray();
Here are a few important considerations when using the batch operation:
- boosts the performance, since it perform multiple operations using one call. These methods returns the matching results in one result object back to the client. This allows the client and server to utilize the network bandwidth in an efficient manner. In some cases, these batch operations can be up to 10 times faster than multiple single based operations.
- should be handled with care, since they can return a large data set (potentially all the space data). This might cause an out of memory error in the space and client process. You should use the GSIterator to return the result in batches (paging) in such cases.
- dos not support timeout operations. The simple way to achieve this is by calling the
read
operation first with the proper timeout, and if non-null values are returned, perform the batch operation. - Exception handling - operation many throw the following Exceptions. ReadMultipleException
Read if exists
A readIfExists operation will return a matching object, or a null if there is currently no matching object in the space. If the only possible matches for the template have conflicting locks from one or more other transactions, the timeout value specifies how long the client is willing to wait for interfering transactions to settle before returning a value. If at the end of that time no value can be returned that would not interfere with transactional state, null is returned. Note that, due to the remote nature of the space, read and readIfExists may throw a RemoteException if the network or server fails prior to the timeout expiration.
Example:
Employee employee = new Employee("Last Name", new Integer(32));
employee.setFirstName("first name");
space.write(employee);
SQLQuery<Employee> query = new SQLQuery<Employee>(Employee.class,
"firstName='first name'");
Employee e = space.readIfExists(query);
Asynchronous Read
The GigaSpace interface supports asynchronous (non-blocking) read operations through the GigaSpace interface. It returns a Future<T> object, where T is the type of the object the request returns. Future
Alternatively, asyncRead also accept an implementation of AsyncFutureListener, which will have its AsyncFutureListener.onResult
method called when the result has been populated. This does not affect the return type of the Future<T>
, but provides an additional mechanism for handling the asynchronous response.
Example:
Employee employee = new Employee("Last Name", new Integer(32));
employee.setFirstName("first name");
space.write(employee);
Integer[] ids = new Integer[] { 31, 32 };
IdsQuery<Employee> query = new IdsQuery<Employee>(Employee.class, ids);
AsyncFuture<Employee> result = space.asyncRead(query);
// This part of the code could be executed in a different Thread
try {
Employee e = result.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
Passing an AsyncFutureListener with Java 8 lambda syntax:
Employee employee = new Employee("Last Name", new Integer(32));
employee.setFirstName("first name");
space.write(employee);
Integer[] ids = new Integer[] { 31, 32 };
IdsQuery<Employee> query = new IdsQuery<Employee>(Employee.class, ids);
AsyncFuture<Employee> result = space.asyncRead(query, (result) -> {
System.out.println("Got a result: " + result.getResult());
});
// This part of the code could be executed in a different Thread
try {
Employee e = result.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
Modifiers
The read operations can be configured with different modifiers.
Examples:
Employee template = new Employee();
// Read objects in a FIFO mode
Employee e = space.read(template, 0, ReadModifiers.FIFO);
// Dirty read
Employee e = space.read(template, 0, ReadModifiers.DIRTY_READ);
For further details on each of the available modifiers see: ReadModifiers
Read by template:Java API
<T> T read(T template) throws DataAccessException
<T> T read(T template, long timeout, ReadModifiers modifiers)throws DataAccessException
.....
Read by Id:Java API
<T> T readById(Class<T> clazz, Object id) throws DataAccessException
<T> T readById(Class<T> clazz, Object id, Object routing, long timeout, ReadModifiers modifiers)throws DataAccessException
.....
Read by ISpaceQuery:Java API
<T> T read(ISpaceQuery<T> query, Object id)throws DataAccessException
<T> T read(ISpaceQuery<T> query, Object routing, long timeout, ReadModifiers modifiers)throws DataAccessException
....
Read multiple:Java API
<T> T[] readMultiple(ISpaceQuery<T> query) throws DataAccessException
<T> T[] readMultiple(ISpaceQuery<T> query, long timeout, ReadModifiers modifiers) throws DataAccessException
<T> T[] readMultiple(T template) throws DataAccessException
<T> T[] readMultiple(T template, long timeout, ReadModifiers modifiers) throws DataAccessException
<T> T[] readMultiple(ISpaceQuery<T> template, int maxEntries, ReadModifiers modifiers) throws DataAccessException
...
Asynchronous Read:Java API
<T> AsyncFuture<T> asyncRead(T template) throws DataAccessException
<T> AsyncFuture<T> asyncRead(T template, long timeout, ReadModifiers modifiers, AsyncFutureListener<T> listener) throws DataAccessException
<T> AsyncFuture<T> asyncRead(ISpaceQuery<T> query)throws DataAccessException
<T> AsyncFuture<T> asyncRead(ISpaceQuery<T> query, long timeout, ReadModifiers modifiers, AsyncFutureListener<T> listener)throws DataAccessException
.....
Read if exists:Java API
<T> T readIfExists(T template)throws DataAccessException
<T> T readIfExistsById(Class<T> clazz, Object id)throws DataAccessException
<T> T readIfExistsById(Class<T> clazz, Object id, Object routing, long timeout, ReadModifiers modifiers) throws DataAccessException
<T> T readIfExistsById(IdQuery<T> query, long timeout, ReadModifiers modifiers) throws DataAccessException
....
Modifier and Type | Description | Default | Unit |
---|---|---|---|
T | POJO, SpaceDocument | ||
timeout | Time to wait for the response | 0 | milliseconds |
query | ISpaceQuery | ||
AsyncFutureListener | Allows to register for a callback on an AsyncFuture to be notified when a result arrives | ||
ReadModifiers | Provides modifiers to customize the behavior of read operations | NONE |
The Take Operation
The take
operations behave exactly like the corresponding read
operations, except that the matching object is removed from the space on one atomic operation. Two take
operations will never return copies of the same object, although if two equivalent objects were in the space the two take
operations could return equivalent objects.
If a take
returns a non-null value, the object has been removed from the space, possibly within a transaction. This modifies the claims to once-only retrieval: A take is considered to be successful only if all enclosing transactions commit successfully.
If a RemoteException
is thrown, the take may or may not have been successful.
If an UnusableEntryException
is thrown, the take removed
the unusable object from the space.
If any other exception is thrown, the take did not occur, and no object was removed from the space.
If you would like to take objects from the space in the same order they have been written into the space you should perform the take objects in a FIFO mode.
Taking an object from the space might generate notifications to registered objects/queries.
The take operation can be performed with the following options:
- Template matching
- By Id
- By IdQuery
- By SQLQuery
To learn more about the different options refer to Querying the Space
Examples:
The following example writes an Employee
object into the space and removes it from the space :
Employee employee = new Employee("Last Name", new Integer(32));
employee.setFirstName("first name");
space.write(employee);
// Take by template
Employee template = new Employee(new Integer(32));
Employee e = space.take(template);
// Take by id
Employee e = space.takeById(Employee.class, new Integer(32));
// Take by IdQuery
IdQuery<Employee> query = new IdQuery<Employee>(Employee.class,
new Integer(32));
Employee e = space.take(query);
// Take by SQLQuery
SQLQuery<Employee> query = new SQLQuery<Employee>(Employee.class,
"firstName='first name'");
Employee e = space.take(query);
Take multiple
The GigaSpace interface provides simple way to perform bulk take operations. You may take large amount of objects in one call.
To remove a batch of objects without returning these back into the client use GigaSpace.clear(SQLQuery)
;
Examples:
Employee emps[] = new Employee[2];
emps[0] = new Employee("Last Name A", new Integer(31));
emps[1] = new Employee("Last Name B", new Integer(32));
space.writeMultiple(emps);
// Take multiple by template
Employee[] employees = space.takeMultiple(Employee.class);
// Take multiple by SQLQuery
SQLQuery<Employee> query = new SQLQuery<Employee>(Employee.class,
"lastName ='Last Name B'");
Employee[] e = space.takeMultiple(query);
// Take by Ids
Integer[] ids = new Integer[] { 31, 32 };
TakeByIdsResult<Employee> result = space.takeByIds(Employee.class,ids);
Employee[] employees = result.getResultsArray();
// Take by IdsQuery
Integer[] ids = new Integer[] { 31, 32 };
IdsQuery<Employee> query = new IdsQuery<Employee>(Employee.class, ids);
TakeByIdsResult<Employee> result = space.takeByIds(query);
Employee[] employees = result.getResultsArray();
Here are a few important considerations when using the batch operation:
- boosts the performance, since it performs multiple operations using one call. This method returns the matching results in one result object back to the client. This allows the client and server to utilize the network bandwidth in an efficient manner. In some cases, this batch operation can be up to 10 times faster than multiple single based operations.
- should be handled with care, since it can return a large data set (potentially all the space data). This might cause an out of memory error in the space and client process. You should use the GSIterator to return the result in batches (paging) in such cases.
- should be performed with transactions - this allows the client to roll back the space to its initial state prior the operation was started, in case of a failure.
- operation dos not support timeout operations. The simple way to achieve this is by calling the
read
operation first with the proper timeout, and if non-null values are returned, perform the batch operation. - in the event of a take error, DataAccessException will wrap a TakeMultipleException, accessible via DataAccessException.getRootCause().
Take if exists
A takeIfExists operation will return a matching object, or a null if there is currently no matching object in the space. If the only possible matches for the template have conflicting locks from one or more other transactions, the timeout value specifies how long the client is willing to wait for interfering transactions to settle before returning a value. If at the end of that time no value can be returned that would not interfere with transactional state, null is returned.
Example:
Employee employee = new Employee("Last Name", new Integer(32));
employee.setFirstName("first name");
space.write(employee);
SQLQuery<Employee> query = new SQLQuery<Employee>(Employee.class,
"firstName='first name'");
Employee e = space.takeIfExists(query);
Asynchronous Take
The GigaSpace interface supports asynchronous (non-blocking) take operations through the GigaSpace interface. It returns a Future<T> object, where T is the type of the object the request returns. Future
Alternatively, asyncTake also accept an implementation of AsyncFutureListener, which will have its AsyncFutureListener.onResult
method called when the result has been populated. This does not affect the return type of the Future<T>
, but provides an additional mechanism for handling the asynchronous response.
Example:
Employee employee = new Employee("Last Name", new Integer(32));
employee.setFirstName("first name");
space.write(employee);
Integer[] ids = new Integer[] { 31, 32 };
IdsQuery<Employee> query = new IdsQuery<Employee>(Employee.class, ids);
AsyncFuture<Employee> result = space.asyncTake(query);
try {
Employee e = result.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
Passing an AsyncFutureListener with Java 8 lambda syntax:
Employee employee = new Employee("Last Name", new Integer(32));
employee.setFirstName("first name");
space.write(employee);
Integer[] ids = new Integer[] { 31, 32 };
IdsQuery<Employee> query = new IdsQuery<Employee>(Employee.class, ids);
AsyncFuture<Employee> result = space.asyncTake(query, (result) -> {
System.out.println("Got result: " + result.getResult());
});
try {
Employee e = result.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
Modifiers
The take operations can be configured with different modifiers.
Examples:
Employee template = new Employee();
// Takes objects in a FIFO mode
Employee e = space.take(template, 0, TakeModifiers.FIFO);
// Takes objects according to FIFO group
Employee e = space.take(template, 0, TakeModifiers.FIFO_GROUPING_POLL);
For further details on each of the available modifiers see: TakeModifiers
Take by template:Java API
<T> T take(T template) throws DataAccessException
<T> T take(T template, long timeout, TakeModifiers modifiers)throws DataAccessException
.....
Take by Id:Java API
<T> T takeById(Class<T> clazz, Object id) throws DataAccessException
<T> T takeById(Class<T> clazz, Object id, Object routing, long timeout, TakeModifiers modifiers)throws DataAccessException
.....
Take by ISpaceQuery:Java API
<T> T take(ISpaceQuery<T> query, Object id)throws DataAccessException
<T> T take(ISpaceQuery<T> query, Object routing, long timeout, TakeModifiers modifiers)throws DataAccessException
....
Take multiple:Java API
<T> T[] takeMultiple(ISpaceQuery<T> query) throws DataAccessException
<T> T[] takeMultiple(ISpaceQuery<T> query, long timeout, TakeModifiers modifiers) throws DataAccessException
<T> T[] takeMultiple(T template) throws DataAccessException
<T> T[] takeMultiple(T template, long timeout, TakeModifiers modifiers) throws DataAccessException
<T> T[] takeMultiple(ISpaceQuery<T> template, int maxEntries, TakeModifiers modifiers) throws DataAccessException
...
Asynchronous take:Java API
<T> AsyncFuture<T> asyncTake(T template) throws DataAccessException
<T> AsyncFuture<T> asyncTake(T template, long timeout, TakeModifiers modifiers, AsyncFutureListener<T> listener) throws DataAccessException
<T> AsyncFuture<T> asyncTake(ISpaceQuery<T> query)throws DataAccessException
<T> AsyncFuture<T> asyncTake(ISpaceQuery<T> query, long timeout, TakeModifiers modifiers, AsyncFutureListener<T> listener)throws DataAccessException
.....
Take if exists:Java API
<T> T takeIfExists(T template)throws DataAccessException
<T> T takeIfExistsById(Class<T> clazz, Object id)throws DataAccessException
<T> T takeIfExistsById(Class<T> clazz, Object id, Object routing, long timeout, TakeModifiers modifiers) throws DataAccessException
<T> T takeIfExistsById(IdQuery<T> query, long timeout, TakeModifiers modifiers) throws DataAccessException
....
Modifier and Type | Description | Default | Unit |
---|---|---|---|
T | POJO, SpaceDocument | ||
timeout | Time to wait for the response | 0 | milliseconds |
query | ISpaceQuery | ||
AsyncFutureListener | Allows to register for a callback on an AsyncFuture to be notified when a result arrives | ||
TakeModifiers | Provides modifiers to customize the behavior of take operations | NONE |
The Clear Operation
You can use GigaSpace.clear
to remove objects from the space. When using the clear operation no object/objects are returned.
Examples:
GigaSpace space;
// Clear by Template
Employee employee = new Employee("Last Name", new Integer(32));
space.clear(employee);
// Clear by SQLQuery
String querystr = "age > 30";
SQLQuery query = new SQLQuery(Employee.class, querystr);
space.clear(query);
// Clear by IdQuery
IdQuery<Employee> query = new IdQuery<Employee>(Employee.class,
new Integer(32));
space.clear(query);
// Clear with Modifier
SQLQuery<Employee> query = new SQLQuery<Employee>(Employee.class,
"firstName='first name'");
space.clear(query, ClearModifiers.EVICT_ONLY);
Clears objects from space.Java API
void clear(T entry) throws DataAccessException
void clear(T entry, ClearModifiers modifiers) throws DataAccessException
void clear(ISpaceQuery<T> query) throws DataAccessException
......
Modifier and Type | Description | default |
---|---|---|
T | POJO, SpaceDocument | |
query | SQLQuery, IdQuery | |
ClearModifiers | Provides modifiers to customize the behavior of the clear operations | NONE |
The Count Operation
You can use GigaSpace.count
to count objects in a space.
Examples:
GigaSpace space;
// Count with Template
Employee employee = new Employee("Last Name");
int count = space.count(employee);
// Count with SQLQuery
String querystr = "age > 30";
SQLQuery query = new SQLQuery(Employee.class, querystr);
int count = space.count(query);
// Count with IdsQuery
Integer[] ids = new Integer[] { 32, 33, 34 };
IdsQuery<Employee> query = new IdsQuery<Employee>(Employee.class, ids);
int count = space.count(query);
// Count with Modifier
SQLQuery<Employee> query = new SQLQuery<Employee>(Employee.class,
"firstName='first name'");
int count = space.count(query, CountModifiers.EXCLUSIVE_READ_LOCK);
Count objects in space.Java API
int count(T entry) throws DataAccessException
int count(T entry, ClearModifiers modifiers) throws DataAccessException
int count(ISpaceQuery<T> query) throws DataAccessException
......
Modifier and Type | Description | default |
---|---|---|
T | POJO, SpaceDocument | |
query | SQLQuery, IdQuery | |
CountModifiers | Provides modifiers to customize the behavior of the count operations | NONE |
Counters
The ISpaceProxy.Change
API allows you to increment or decrement an Numerical field within your Space object or Document. This change may operate on a numeric property only (byte,short,int,long,float,double) or their corresponding Boxed variation. To maintain a counter you should use the Change operation with the ChangeSet
increment/decrement method that adds/subtract the provided numeric value to the existing counter.
Example:
Incrementing a Counter done using the ChangeSet().Increment
call:
GigaSpace space = // ... obtain a space reference
String id = "myID";
IdQuery<WordCount> idQuery = new IdQuery<WordCount>(WordCount.class, id);
space.change(idQuery, new ChangeSet().increment("mycounter", 1));
Getting the Counter value via the read call:
GigaSpace space = // ... obtain a space reference
String id = "myID";
IdQuery<WordCount> idQuery = new IdQuery<WordCount>(WordCount.class, id);
WordCount wordount = space.readById(WordCount.class , idQuery);
int counterValue = wordount.getMycounter();
Aggregators
There is no need to retrieve the entire data set from the space to the client side , iterate the result set and perform the aggregation. This would be an expensive activity as it might return large amount of data into the client application. The Aggregators allow you to perform the entire aggregation activity at the space side avoiding any data retrieval back to the client side.
Example:
import static org.openspaces.extensions.QueryExtension.*;
...
SQLQuery<Person> personSQLQuery = new SQLQuery<Person>();
// retrieve the maximum value stored in the field "age"
Number maxAgeInSpace = maxValue(space, personSQLQuery, "age");
/// retrieve the minimum value stored in the field "age"
Number minAgeInSpace = minValue(space, personSQLQuery, "age");
// Sum the "age" field on all space objects.
Number combinedAgeInSpace = sum(space, personSQLQuery, "age");
// Sum's the "age" field on all space objects then divides by the number of space objects.
Double averageAge = average(space, personSQLQuery, "age");
// Retrieve the space object with the highest value for the field "age".
Person oldestPersonInSpace = maxEntry(space, personSQLQuery, "age");
/// Retrieve the space object with the lowest value for the field "age".
Person youngestPersonInSpace = minEntry(space, personSQLQuery, "age");
@SpaceClass
public class Person {
private Long id;
private Long age;
private String country;
@SpaceId(autoGenerate=false)
public Long getId() {
return id;
}
public Person setId(Long id) {
this.id = id;
return this;
}
public Long getAge() {
return age;
}
public Person setAge(Long age) {
this.age = age;
return this;
}
@SpaceIndex
public String getCountry() {
return country;
}
public Person setCountry(String country) {
this.country = country;
return this;
}
}
Async Extension
When running with Java8, it is possible to have an even simpler Space API with the AsyncExtension
.
AsyncExtension substituts the Space AsyncFuture
with the Java8 CompletableFuture
and thus can make the code more fluent.
There is no need to retrieve the entire data set from the Space to the client side , iterate the result set and perform the aggregation. This would be an expensive activity as it might return a large amount of data into the client application. The Aggregators
allow you to perform the entire aggregation activity at the Space side avoiding any data retrieval back to the client side.
Example:
import static org.openspaces.extensions.AsyncExtension.asyncRead;
asyncRead(gigaSpace, template).thenAccept(value -> {
System.out.println("got " + value);
})