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SQL Component

The The sql: component  component allows you to work with databases using JDBC queries. The difference between this component and and JDBC component  component is that in case of SQL the query is a property of the endpoint and it uses message payload as parameters passed to the query.

This component uses uses spring-jdbc behind  behind the scenes for the actual SQL handling.

Maven users will need to add the following dependency to their their pom.xml for  for this component:

Code Block
languagexml
<dependency> 
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-sql</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

The SQL component also supports:

  • a JDBC based repository for the the Idempotent Consumer EIP  EIP pattern. See further below.
  • a JDBC based repository for the the Aggregator EIP  EIP pattern. See further below.

URI format

From Camel 2.11 onwards this component can create both consumer (e.g. from()) and producer endpoints (e.g. to()).

In previous versions, it could only act as a producer.

This component can be used as

...

Transactional Client.

The SQL component uses the following endpoint URI notation:

Code Block
languagejava
sql:select * from table where id=# order by name[?options]

 

From Camel 2.11 onwards you can use named parameters by using :#name_of_the_parameter style  style as shown:

...

Code Block
languagejava
 sql:select * from table where id=:#myId order by name[?options]

When using named parameters, Camel will lookup the names from, in the given precedence:
1. from message body if its a java.util.Map
2. from message headers

If a named parameter cannot be resolved, then an exception is thrown.

From From Camel 2.14 onward  onward you can use Simple expressions as parameters as shown:

Code Block
languagejava
sql:select * from table where id=:#${property.myId} order by name[?options]

Notice that the standard standard ? symbol  symbol that denotes the parameters to an SQL query is substituted with the the # symbol symbol, because the the ? symbol  symbol is used to specify options for the endpoint. The The ? symbol  symbol replacement can be configured on endpoint basis.

From From Camel 2.17 onwards  onwards you can externalize your SQL queries to files in the classpath or file system as shown:

Code Block
languagejava
sql:classpath:sql/myquery.sql[?options]

And the myquery.sql file is in the classpath and is just a plain text

...

Code Block
languagesql
select * from table where id = :#${property.myId} order by

...

 name 

In the file you can use multilines and format the SQL as you wish. And also use comments such as the – dash line.

You can append query options to the URI in the following format, ?option=value&option=value&...

Options

...

Option

Type

Default

Description

batch

boolean

false

Camel 2.7.5, 2.8.4 and 2.9: Execute SQL batch update statements. See notes below on how the treatment of the inbound message body changes if this is set to true.

dataSourceRef

String

null

Deprecated and will be removed in Camel 3.0: Reference to a DataSource to look up in the registry. Use dataSource=#theName instead.

dataSource

String

null

Camel 2.11: Reference to a DataSource to look up in the registry.

placeholder

String

#

Camel 2.4: Specifies a character that will be replaced to ? in SQL query. Notice, that it is simple String.replaceAll() operation and no SQL parsing is involved (quoted strings will also change). This replacement is only happening if the endpoint is created using the SqlComponent. If you manually create the endpoint, then use the expected ? sign instead.

usePlaceholderbooleantrueCamel 2.17: Sets whether to use placeholder and replace all placeholder characters with ? sign in the SQL queries.

template.<xxx>

 

null

Sets additional options on the Spring JdbcTemplate that is used behind the scenes to execute the queries. For instance, template.maxRows=10. For detailed documentation, see the JdbcTemplate javadoc documentation.

allowNamedParameters

boolean

true

Camel 2.11: Whether to allow using named parameters in the queries.

processingStrategy

 

 

Camel 2.11: SQL consumer only: Allows to plugin to use a custom org.apache.camel.component.sql.SqlProcessingStrategy to execute queries when the consumer has processed the rows/batch.

prepareStatementStrategy

 

 

Camel 2.11: Allows to plugin to use a custom org.apache.camel.component.sql.SqlPrepareStatementStrategy to control preparation of the query and prepared statement.

consumer.delay

long

500

Camel 2.11: SQL consumer only: Delay in milliseconds between each poll.

consumer.initialDelay

long

1000

Camel 2.11: SQL consumer only: Milliseconds before polling starts.

consumer.useFixedDelay

boolean

false

Camel 2.11: SQL consumer only: Set to true to use fixed delay between polls, otherwise fixed rate is used. See ScheduledExecutorService in JDK for details.

maxMessagesPerPoll

int

0

Camel 2.11: SQL consumer only: An integer value to define the maximum number of messages to gather per poll. By default, no maximum is set.

useIterator

boolean

true

Camel 2.11: SQL consumer only: If true each row returned when polling will be processed individually. If false the entire java.util.List of data is set as the IN body. Notice in Camel 2.15.x or older you need to prefix this option with consumer., eg consumer.useIterator=true.

routeEmptyResultSet

boolean

false

Camel 2.11: SQL consumer only: Whether to route a single empty Exchange if there was no data to poll. Notice in Camel 2.15.x or older you need to prefix this option with consumer., eg consumer.useIterator=true.

onConsume

String

null

Camel 2.11: SQL consumer only: After processing each row then this query can be executed, if the Exchange was processed successfully, for example to mark the row as processed. The query can have parameter. Notice in Camel 2.15.x or older you need to prefix this option with consumer., eg consumer.useIterator=true.

onConsumeFailed

String

null

Camel 2.11: SQL consumer only: After processing each row then this query can be executed, if the Exchange failed, for example to mark the row as failed. The query can have parameter. Notice in Camel 2.15.x or older you need to prefix this option with consumer., eg consumer.useIterator=true.

onConsumeBatchComplete

String

null

Camel 2.11: SQL consumer only: After processing the entire batch, this query can be executed to bulk update rows etc. The query cannot have parameters. Notice in Camel 2.15.x or older you need to prefix this option with consumer., eg consumer.useIterator=true.

expectedUpdateCount

int

-1

Camel 2.11: SQL consumer only: If using consumer.onConsume then this option can be used to set an expected number of rows being updated. Typically you may set this to 1 to expect one row to be updated. Notice in Camel 2.15.x or older you need to prefix this option with consumer., eg consumer.useIterator=true.

breakBatchOnConsumeFail

boolean

false

Camel 2.11: SQL consumer only: If using consumer.onConsume and it fails, then this option controls whether to break out of the batch or continue processing the next row from the batch. Notice in Camel 2.15.x or older you need to prefix this option with consumer., eg consumer.useIterator=true.

alwaysPopulateStatement

boolean

false

Camel 2.11: SQL producer only: If enabled then the populateStatement method from org.apache.camel.component.sql.SqlPrepareStatementStrategy is always invoked, also if there is no expected parameters to be prepared. When this is false then the populateStatement is only invoked if there is 1 or more expected parameters to be set; for example this avoids reading the message body/headers for SQL queries with no parameters.

separator

char

,

Camel 2.11.1: The separator to use when parameter values is taken from message body (if the body is a String type), to be inserted at # placeholders. Notice if you use named parameters, then a Map type is used instead.

outputType

String

SelectList

Camel 2.12.0: outputType='SelectList', for consumer or producer,

...

will output a List of Map. SelectOne will output single Java object in the following way:
a) If the query has only single column, then that JDBC Column object is returned. (such as SELECT COUNT( * ) FROM PROJECT will return a Long object.
b) If the query has more than one column, then it will return a Map of that result.
c) If the outputClass is set, then it will convert the query result into an Java bean object by calling all the setters that match the column names. It will assume your class has a default constructor to create instance with.
d) If the query resulted in more than one rows, it throws an non-unique result exception.

From Camel 2.14.1 onwards the SelectList also supports mapping each row to a Java object as the SelectOne does (only step c).

From Camel 2.18 onwards there is a new StreamList outputType that streams the result of the query using an Iterator. It can be used with the Splitter EIP in streaming mode to process the ResultSet in streaming fashion. This StreamList do not support batch mode, but you can use outputClass to map each row to a class.

outputClass

String

null

Camel 2.12.0: Specify the full package and class name to use as conversion when outputType=SelectOne.

outputHeader

Stringnull

Camel 2.15: To store the result as a header instead of the message body. This allows to preserve the existing message body as-is.

parametersCount

int

0

Camel 2.11.2/2.12.0 If set greater than zero, then Camel will use this count value of parameters to replace instead of querying via JDBC metadata API. This is useful if the JDBC vendor could not return correct parameters count, then user may override instead.

noop

boolean

false

Camel 2.12.0 If set, will ignore the results of the SQL query and use the existing IN message as the OUT message for the continuation of processing

useMessageBodyForSqlbooleanfalseCamel 2.16: Whether to use the message body as the SQL and then headers for parameters. If this option is enabled then the SQL in the uri is not used. The SQL parameters must then be provided in a header with the key CamelSqlParameters. This option is only for the producer.
transactedbooleanfalseCamel 2.16.2: SQL consumer only:Enables or disables transaction. If enabled then if processing an exchange failed then the consumer break out processing any further exchanges to cause a rollback eager

Treatment of the message body

The SQL component tries to convert the message body to an object of of java.util.Iterator type  type and then uses this iterator to fill the query parameters (where each query parameter is represented by a # symbol  symbol (or configured placeholder) in the endpoint URI). If the message body is not an array or collection, the conversion results in an iterator that iterates over only one object, which is the body itself.

For example, if the message body is an instance of of java.util.List, the first item in the list is substituted into the first occurrence of of # in  in the SQL query, the second item in the list is substituted into the second occurrence of of #, and so on.

If If batch is  is set to to true, then the interpretation of the inbound message body changes slightly – instead of an iterator of parameters, the component expects an iterator that contains the parameter iterators; the size of the outer iterator determines the batch size.

From Camel 2.16 onwards you can use the option useMessageBodyForSql option useMessageBodyForSql that allows to use the message body as the SQL statement, and then the SQL parameters must be provided in a header with the key SqlConstants.SQL_PARAMETERS. This allows the SQL component to work more dynamic as the SQL query is from the message body.

Result of the query

For For select operations operations, the result is an instance of of List<Map<String, Object>> type type, as returned by the the JdbcTemplate.queryForList() method method. For For update operations operations, the result is the number of updated rows, returned as an an Integer.

By default, the result is placed in the message body.  If the outputHeader parameter is set, the result is placed in the header.  This is an alternative to using a full message enrichment pattern to add headers, it provides a concise syntax for querying a sequence or some other small value into a header.  It is convenient to use outputHeader and outputType together:

Code Block
languagejava
from("jms:order.inbox")
    .to("sql:select order_seq.nextval from dual?outputHeader=OrderId&outputType=SelectOne")
    .to("jms:order.booking");

Using StreamList

From Camel  Camel 2.18 onwards  onwards the producer supports outputType=StreamList that uses an iterator to stream the output of the query. This allows to process the data in a streaming fashion which for example can be used by the Splitter EIP  EIP to process each row one at a time, and load data from the database as needed.

Code Block
languagejava
from("direct:withSplitModel")
   .to("sql:select * from projects order by id?outputType=StreamList&outputClass=org.apache.camel.component.sql.ProjectModel")
   .to("log:stream")
   .split(body()).streaming()
       .to("log:row")
       .to("mock:result")
   .end();

...

Header values

When performing performing update operations operations, the SQL Component stores the update count in the following message headers:

Header

Description

CamelSqlUpdateCount

The number of rows updated for update operations, returned as an Integer object. This This header is not provided when using outputType=StreamList.

CamelSqlRowCount

The number of rows returned for select operations, returned as an Integer object. This header is not provided when using outputType=StreamList.

CamelSqlQuery

Camel 2.8: Query to execute. This query takes precedence over the query specified in the endpoint URI. Note that query parameters in the header are represented by a ? instead of a # symbol

When performing insert operations operations, the SQL Component stores the rows with the generated keys and number of these rown in the following message headers (Available as of Camel 2.12.4, 2.13.1):

...

If you insert data using SQL INSERT, then the RDBMS may support auto generated keys. You can instruct the SQL producer to return the generated keys in headers.
To do that set the header header CamelSqlRetrieveGeneratedKeys=true. Then the generated keys will be provided as headers with the keys listed in the table above.

You can see more details in this this unit test.

Configuration

You can now set a reference to a DataSource in  in the URI directly:

...

Code Block
languagesql
 select * from table where id=# order by name?dataSource=myDS

Sample

In the sample below we execute a query and retrieve the result as a List of  of rows, where each row is a Map<String, Object and Object> and the key is the column name.

First, we set up a table to use for our sample. As this is based on an unit test, we do it in java:{snippet:id=e2|lang=java|url=camel/trunk/components/camel-sql/src/test/java/org/apache/camel/component/sql/SqlDataSourceRefTest.java}The SQL script createAndPopulateDatabase.sql we

Code Block
languagejava
db = new EmbeddedDatabaseBuilder()
    .setType(EmbeddedDatabaseType.DERBY).addScript("sql/createAndPopulateDatabase.sql").build();


The SQL script createAndPopulateDatabase.sql we execute looks like as described below:{snippet:id=e1|lang=sql|url=camel/trunk/components/camel-sql/src/test/resources/sql/createAndPopulateDatabase.sql}

Code Block
languagesql
create table projects (id integer primary key, project varchar(10), license varchar(5));
insert into projects values (1, 'Camel', 'ASF');
insert into projects values (2, 'AMQ', 'ASF');
insert into projects values (3, 'Linux', 'XXX');

Then we configure our route and our our sql component component. Notice that we use a direct endpoint  endpoint in front of the the sql endpoint endpoint. This allows us to send an exchange to the the direct endpoint  endpoint with the URI, direct:simple, which is much easier for the client to use than the long long sql: URI URI. Note that the the DataSource is  is looked up up in the registry, so we can use standard Spring XML to configure our our DataSource.{snippet:id=e1|lang=java|url=camel/trunk/components/camel-sql/src/test/java/org/apache/camel/component/sql/SqlDataSourceRefTest.java}

 

Code Block
languagejava
from("direct:simple")
    .to("sql:select * from projects where license = # order by id?dataSource=#jdbc/myDataSource")
    .to("mock:result");

And then we fire the message into the the direct endpoint  endpoint that will route it to our our sql component  component that queries the database.{snippet:id=e3|lang=java|url=camel/trunk/components/camel-sql/src/test/java/org/apache/camel/component/sql/SqlDataSourceRefTest.java}We could configure the DataSource in Spring XML as follows:

...

 

Code Block
languagejava
MockEndpoint mock = getMockEndpoint("mock:result");
mock.expectedMessageCount(1);

// send the query to direct that will route it to the sql where we will execute the query
// and bind the parameters with the data from the body. The body only contains one value
// in this case (XXX) but if we should use multi values then the body will be iterated
// so we could supply a List<String> instead containing each binding value.
template.sendBody("direct:simple", "XXX");

mock.assertIsSatisfied();

// the result is a List
List<?> received = assertIsInstanceOf(List.class, mock.getReceivedExchanges().get(0).getIn().getBody());

// and each row in the list is a Map
Map<?, ?> row = assertIsInstanceOf(Map.class, received.get(0));

// and we should be able the get the project from the map that should be Linux
assertEquals("Linux", row.get("PROJECT"));

We could configure the DataSource in Spring XML as follows:

Code Block
languagejava
<jee:jndi-lookup id="myDS" jndi-name="jdbc/myDataSource"/

]]>

Using named parameters

Available as of Camel 2.11

In the given route below, we want to get all the projects from the projects table. Notice the SQL query has 2 named parameters, :#lic and :#min.
Camel will then lookup for these parameters from the message body or message headers. Notice in the example above we set two headers with constant value
for the named parameters:

java

Code Block
languagejava
from("direct:projects")
   .setHeader("lic", constant("ASF"))
   .setHeader("min", constant(123))
   .to("sql:select * from projects where license = :#lic and id > :#min order by id")

:#min order by id") ]]>

Though if the message body is a java.util.Map then  then the named parameters will be taken from the body.

Code Block
languagejava
from("direct:projects") 
   .to("sql:select * from projects where license = :#lic and id > :#min order by id")

:#min order by id") ]]>

Using expression parameters

...

In the given route below, we want to get all the project from the database. It uses the body of the exchange for defining the license and uses the value of a property as the second parameter.

Code Block
languagejava
from("direct:projects")
   .setBody(constant("ASF"))
   .setProperty("min", constant(123)) 
   .to("sql:select * from projects where license = :#${body} and id > :#${property.min} order by id")

:#${property.min} order by id")]]>

Using IN queries with dynamic values

...

From Camel 2.17 onwards the SQL producer allows to use SQL queries with IN statements where the IN values is dynamic computed. For example from the message body or a header etc.

To use IN you need to:

  • prefix the parameter name with in:
  • add add ( ) around the parameter

An example explains this better. The following query is used:

...

 

Code Block
languagesql
select * from projects where project in (:#in:names) order by

...

 id 


In the following route:

 

Code Block
languagejava
from("direct:query") 
  .to("sql:classpath:sql/selectProjectsIn.sql") 
  .to("log:query") 
  .to("mock:query");


Then the IN query can use a header with the key names with the dynamic values such as:

 

Code Block
languagejava
// use an array 
template.requestBodyAndHeader("direct:query", "Hi there!", "names", new String[]{"Camel", "AMQ"});
 
// use a list 
List<String> names = new ArrayList<String>();
names.add("Camel"); 
names.add("AMQ");
template.requestBodyAndHeader("direct:query", "Hi there!", "names", names);
 
// use a string separated values with comma 
template.requestBodyAndHeader("direct:query", "Hi there!", "names", "Camel,AMQ");

The query can also be specified in the endpoint instead of being externalized (notice that externalizing makes maintaining the SQL queries easier)

Code Block
languagejava
from("direct:query") 
  .to("sql:select * from projects where project in (:#in:names) order by id") 
  .to("log:query") 
  .to("mock:query");

 

Using the JDBC based idempotent repository

Available as of Camel 2.7: In this section we will use the JDBC based idempotent repository.

Abstract

...

class From Camel 2.9 onwards there is an abstract class org.apache.camel.processor.idempotent.jdbc.AbstractJdbcMessageIdRepository you can extend to build custom JDBC idempotent repository.

First we have to create the database table which will be used by the idempotent repository. For For Camel 2.7, we use the following schema:

...

Code Block
languagesql
 sqlCREATE TABLE CAMEL_MESSAGEPROCESSED (
   processorName VARCHAR(255),
   messageId VARCHAR(100) )

...

 

In In Camel 2.8, we added the createdAt column:

...

Code Block
languagesql
 CREATE TABLE CAMEL_MESSAGEPROCESSED (
   processorName VARCHAR(255),
   messageId VARCHAR(100),
   createdAt TIMESTAMP )

...

 The SQL Server TIMESTAMP type is a fixed-length binary-string type. It does not map to any of the JDBC time types: DATETIME, or TIMESTAMP.

 

We recommend to have a unique constraint on the columns processorName and messageId. Because the syntax for this constraint differs for database to database, we do not show it here.

Second we need to setup a javax.sql.DataSource in  in the spring XML file:

 ]]>

Code Block
languagexml
<jdbc:embedded-database id="dataSource" type="DERBY" /> 


And finally we can create our JDBC idempotent repository in the spring XML file as well:

...

 ]]>

Code Block
languagexml
 <bean id="messageIdRepository" class="org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository">  
   <constructor-arg ref="dataSource" /> 
   <constructor-arg value="myProcessorName" />
 </

...

bean> 


Customize the JdbcMessageIdRepository

Starting with with Camel 2.9.1 you  you have a few options to tune the the org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository for  for your needs:

ParameterDefault ValueDescription
createTableIfNotExiststrueDefines whether or not Camel should try to create the table if it doesn't exist.
tableExistsStringSELECT 1 FROM CAMEL_MESSAGEPROCESSED WHERE 1 = 0This query is used to figure out whether the table already exists or not. It must throw an exception to indicate the table doesn't exist.

createString

CREATE TABLE CAMEL_MESSAGEPROCESSED (processorName VARCHAR(255), messageId VARCHAR(100), createdAt TIMESTAMP)

The statement which is used to create the table.
queryStringSELECT COUNT(*) FROM CAMEL_MESSAGEPROCESSED WHERE processorName = ? AND messageId = ?

The query which is used to figure out whether the message already exists in the repository (the result is not equals to '0'). It takes two parameters. This first one is the processor name (String) and the second one is the message id (String).

insertStringINSERT INTO CAMEL_MESSAGEPROCESSED (processorName, messageId, createdAt) VALUES (?, ?, ?)

The statement which is used to add the entry into the table. It takes three parameter. The first one is the processor name (String), the second one is the message id (String) and the third one is the timestamp (java.sql.Timestamp) when this entry was added to the repository.

deleteStringDELETE FROM CAMEL_MESSAGEPROCESSED WHERE processorName = ? AND messageId = ?

The statement which is used to delete the entry from the database. It takes two parameter. This first one is the processor name (String) and the second one is the message id (String).

 

A customized customized org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository could  could look like:

]]>

Code Block
languagexml
<bean id="messageIdRepository" class="org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository">
   <constructor-arg ref="dataSource" />
   <constructor-arg value="myProcessorName" />
   <property name="tableExistsString" value="SELECT 1 FROM CUSTOMIZED_MESSAGE_REPOSITORY WHERE 1 = 0" />
   <property name="createString" value="CREATE TABLE CUSTOMIZED_MESSAGE_REPOSITORY (processorName VARCHAR(255), messageId VARCHAR(100), createdAt TIMESTAMP)" />    
   <property name="queryString" value="SELECT COUNT(*) FROM CUSTOMIZED_MESSAGE_REPOSITORY WHERE processorName = ? AND messageId = ?" />
   <property name="insertString" value="INSERT INTO CUSTOMIZED_MESSAGE_REPOSITORY (processorName, messageId, createdAt) VALUES (?, ?, ?)" />
   <property name="deleteString" value="DELETE FROM CUSTOMIZED_MESSAGE_REPOSITORY WHERE processorName = ? AND messageId = ?" />
</bean>


Using the JDBC based aggregation repository

Available as of Camel 2.6

Using JdbcAggregationRepository in Camel 2.

...

6 In Camel 2.6, the JdbcAggregationRepository is provided in the camel-jdbc-aggregator component. From Camel 2.7 onwards, the JdbcAggregationRepository is provided in the camel-sql component.

JdbcAggregationRepository is an  is an AggregationRepository which  which on the fly persists the aggregated messages. This ensures that you will not loose messages, as the default aggregator will use an in memory only only AggregationRepository.

The The JdbcAggregationRepository allows  allows together with Camel to provide persistent support for the the Aggregator.

It has the following options:

OptionTypeDescription
dataSourceDataSourceMandatory: The javax.sql.DataSource to use for accessing the database.
repositoryNameStringMandatory: The name of the repository.
transactionManagerTransactionManager

Mandatory: The org.springframework.transaction.PlatformTransactionManager to mange transactions for the database. The TransactionManager must be able to support databases.

lobHandlerLobHandlerorg.springframework.jdbc.support.lob.LobHandler to handle Lob types in the database. Use this option to use a vendor specific LobHandler, for example when using Oracle.
returnOldExchangebooleanWhether the get operation should return the old existing Exchange if any existed. By default this option is false to optimize as we do not need the old exchange when aggregating.
useRecoverybooleanWhether or not recovery is enabled. This option is by default true. When enabled the Camel Aggregator automatic recover failed aggregated exchange and have them resubmitted.
recoveryIntervallong

If recovery is enabled then a background task is run every x'th time to scan for failed exchanges to recover and resubmit. By default this interval is 5000 millis.

maximumRedeliveriesintAllows you to limit the maximum number of redelivery attempts for a recovered exchange. If enabled then the Exchange will be moved to the dead letter channel if all redelivery attempts failed. By default this option is disabled. If this option is used then the deadLetterUri option must also be provided.

deadLetterUri

String

An endpoint uri for a Dead Letter Channel where exhausted recovered Exchanges will be moved. If this option is used then the maximumRedeliveries option must also be provided.

storeBodyAsTextboolean

Camel 2.11: Whether to store the message body as String which is human readable. By default this option is false storing the body in binary format.

headersToStoreAsTextList<String>

 Camel 2.11: Allows to store headers as String which is human readable. By default this option is disabled, storing the headers in binary format.

jdbcOptimisticLockingExceptionMapperjdbcOptimisticLockingExceptionMapper

Camel 2.12: Allows to plugin a custom org.apache.camel.processor.aggregate.jdbc.JdbcOptimisticLockingExceptionMapper to map vendor specific error codes to an optimistick locking error, for Camel to perform a retry. This requires optimisticLocking to be enabled.

Optimistic Locking

Optimistic locking is set to on by default.  If two exchanges attempt to insert at the same time an exception will thrown, caught, converted to an OptimisticLockingException, and rethrown.  

What is preserved when persisting

JdbcAggregationRepository will  will only preserve any any Serializable compatible  compatible data types. If a data type is not such a type its dropped and a WARN is  is logged. And it only persists the the Message body  body and the the Message headers headers. The The Exchange properties are  properties are not persisted persisted.

From Camel 2.11 onwards you can store the message body and select(ed) headers as String in separate columns.

Recovery

The The JdbcAggregationRepository will  will by default recover any failed failed Exchange. It does this by having a background tasks that scans for failed failed Exchanges in the persistent store. You can use the the checkInterval option  option to set how often this task runs. The recovery works as transactional which ensures that Camel will try to recover and redeliver the failed failed Exchange. Any Any Exchange which  which was found to be recovered will be restored from the persistent store and resubmitted and send out again.

The following headers is set when an an Exchange is  is being recovered/redelivered:

...

HeaderTypeDescription
Exchange.REDELIVEREDBooleanIs set to true to indicate the Exchange is being redelivered.
Exchange.REDELIVERY_COUNTERIntegerThe redelivery attempt, starting from 1.

 

Only when an an Exchange has  has been successfully processed it will be marked as complete which happens when the the confirm method  method is invoked on the the AggregationRepository. This means if the same same Exchange fails  fails again it will be kept retried until it success.

You can use option option maximumRedeliveries to  to limit the maximum number of redelivery attempts for a given recovered recovered Exchange. You must also set the the deadLetterUri option  option so Camel knows where to send the the Exchange when the  when the maximumRedeliveries was  was hit.

You can see some examples in the unit tests of camel-sql, for example example this test.

Database

To be operational, each aggregator uses two table: the aggregation and completed one. By convention the completed has the same name as the aggregation one suffixed with with "_COMPLETED". The name must be configured in the Spring bean with the the RepositoryName property property. In the following example aggregation will be used.

The table structure definition of both table are identical: in both case a String value is used as key (id) whereas a Blob contains the exchange serialized in byte array.
However one difference should be remembered: the the id field  field does not have the same content depending on the table.
In the aggregation table table id holds  holds the correlation Id used by the component to aggregate the messages. In the completed table, id holds  holds the id of the exchange stored in corresponding the blob field.

Here is the SQL query used to create the tables, just replace replace "aggregation" with  with your aggregator repository name.

...

Code Block
languagesql
CREATE TABLE aggregation (
 id varchar(255) NOT NULL,
 exchange blob NOT NULL,
 constraint aggregation_pk PRIMARY KEY (id) 
);
 
CREATE TABLE aggregation_completed (
 id varchar(255) NOT NULL,
 exchange blob NOT NULL,
 constraint aggregation_completed_pk PRIMARY KEY (id) 
);

Storing body and headers as text

Available as of Camel 2.11

You can configure the the JdbcAggregationRepository to  to store message body and select(ed) headers as String in separate columns. For example to store the body, and the following two headers headers companyName and  and accountName use  use the following SQL:

Code Block
languagesql
CREATE TABLE aggregationRepo3 (
 id varchar(255) NOT NULL, 
 exchange blob NOT NULL, 
 body varchar(1000),
 companyName varchar(1000),
 accountName varchar(1000),
 constraint aggregationRepo3_pk PRIMARY KEY (id) 
);
 
CREATE TABLE aggregationRepo3_completed (
 id varchar(255) NOT NULL,
 exchange blob NOT NULL,
 body varchar(1000),
 companyName varchar(1000),
 accountName varchar(1000),
 constraint aggregationRepo3_completed_pk PRIMARY KEY (id) 
); 

And then configure the repository to enable this behavior as shown below:

...

Code Block
languagexml
<bean id="repo3" class="org.apache.camel.processor.aggregate.jdbc.JdbcAggregationRepository">
    <property name="repositoryName" value="aggregationRepo3"/>
    <property name="transactionManager" ref="txManager3"/>
    <property name="dataSource" ref="dataSource3"/>
    <!-- configure to store the message body and following headers as text in the repo -->
    <property name="storeBodyAsText" value="true"/>
    <property name="headersToStoreAsText">
       <list>
           <value>companyName</value>
           <value>accountName</value>
       </list>
    </property>
 </bean>


Codec (Serialization)

Since they can contain any type of payload, Exchanges are not serializable by design. It is converted into a byte array to be stored in a database BLOB field. All those conversions are handled by the the JdbcCodec class class. One detail of the code requires your attention: the the ClassLoadingAwareObjectInputStream.

The The ClassLoadingAwareObjectInputStream has  has been reused from the the Apache ActiveMQ project project. It wraps an an ObjectInputStream and  and use it with the the ContextClassLoader rather  rather than the the currentThread one one. The benefit is to be able to load classes exposed by other bundles. This allows the exchange body and headers to have custom types object references.

Transaction

A Spring Spring PlatformTransactionManager is  is required to orchestrate transaction.

Service (Start/Stop)

The The start method  method verify the connection of the database and the presence of the required tables. If anything is wrong it will fail during starting.

...

Depending on the targeted environment, the aggregator might need some configuration. As you already know, each aggregator should have its own repository (with the corresponding pair of table created in the database) and a data source. If the default lobHandler is not adapted to your database system, it can be injected with the the lobHandler property property.

Here is the declaration for Oracle:

...

Code Block
languagejava
<bean id="lobHandler" class="org.springframework.jdbc.support.lob.OracleLobHandler">
  <property name="nativeJdbcExtractor" ref="nativeJdbcExtractor"/>
</bean> 
<bean id="nativeJdbcExtractor" class="org.springframework.jdbc.support.nativejdbc.CommonsDbcpNativeJdbcExtractor"/>
<bean id="repo" class="org.apache.camel.processor.aggregate.jdbc.JdbcAggregationRepository">
    <property name="transactionManager" ref="transactionManager"/>
    <property name="repositoryName" value="aggregation"/>
    <property name="dataSource" ref="dataSource"/>
    <!-- Only with Oracle, else use default -->
    <property name="lobHandler" ref="lobHandler"/>
</bean>

Optimistic locking

From From Camel 2.12 onwards  onwards you can turn on on optimisticLocking and  and use this JDBC based aggregation repository in a clustered environment where multiple Camel applications shared the same database for the aggregation repository. If there is a race condition there JDBC driver will throw a vendor specific exception which the the JdbcAggregationRepository can  can react upon. To know which caused exceptions from the JDBC driver is regarded as an optimistick locking error we need a mapper to do this. Therefore there is a org.apache.camel.processor.aggregate.jdbc.JdbcOptimisticLockingExceptionMapper allows  allows you to implement your custom logic if needed. There is a default implementation implementation org.apache.camel.processor.aggregate.jdbc.DefaultJdbcOptimisticLockingExceptionMapper which  which works as follows:

The following check is done:

If the caused exception is an an SQLException then  then the SQLState is checked if starts with 23.

If the caused exception is a DataIntegrityViolationException

...

Here is an example, where we define 2 extra FQN class names from the JDBC vendor.

...

 

Code Block
languagexml
<bean id="repo" class="org.apache.camel.processor.aggregate.jdbc.JdbcAggregationRepository">
   <property name="transactionManager" ref="transactionManager"/>
   <property name="repositoryName" value="aggregation"/> 
   <property name="dataSource" ref="dataSource"/>
   <property name"jdbcOptimisticLockingExceptionMapper" ref="myExceptionMapper"/>
</bean> 
<!-- use the default mapper with extra FQN class names from our JDBC driver --> 
<bean id="myExceptionMapper" class="org.apache.camel.processor.aggregate.jdbc.DefaultJdbcOptimisticLockingExceptionMapper">
   <property name="classNames"> 
     <util:set> 
       <value>com.foo.sql.MyViolationExceptoion</value>
       <value>com.foo.sql.MyOtherViolationExceptoion</value>
     </util:set>
   </property>
</

...

bean> 

 

Endpoint See Also

Endpoint 

SQL Stored Procedure

JDBC