SQL Component
The sql: component allows you to work with databases using JDBC queries. The difference between this component and JDBC 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 spring-jdbc
behind the scenes for the actual SQL handling.
Maven users will need to add the following dependency to their pom.xml
for this component:
<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 Idempotent Consumer EIP pattern. See further below.
- a JDBC based repository for the Aggregator EIP pattern. See further below.
URI format
In Camel 2.10 or older the SQL component can only be used as producer.
From Camel 2.11 onwards this component can also be a consumer, eg from()
.
This component can be used as a Transactional Client.
The SQL component uses the following endpoint URI notation:
sql:select * from table where id=# order by name[?options]
Notice that the standard ?
symbol that denotes the parameters to an SQL query is substituted with the #
symbol, because the ?
symbol is used to specify options for the endpoint. The ?
symbol replacement can be configured on endpoint basis.
You can append query options to the URI in the following format, ?option=value&option=value&...
Options
Option |
Type |
Default |
Description |
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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 |
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Reference to a |
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Camel 2.4: Specifies a character that will be replaced to |
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Sets additional options on the Spring |
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Camel 2.11: SQL consumer only: Delay in milliseconds between each poll. |
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Camel 2.11: SQL consumer only: Milliseconds before polling starts. |
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Camel 2.11: SQL consumer only: Set to |
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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. |
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Camel 2.11: SQL consumer only: If |
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Camel 2.11: SQL consumer only: Whether to route a single empty Exchange if there was no data to poll. |
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Camel 2.11: SQL consumer only: After processing each row then this query can be executed to for example delete or mark the row as processed. The query can have parameter. |
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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. |
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Camel 2.11: SQL consumer only: If using |
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Camel 2.11: SQL consumer only: If using |
Treatment of the message body
The SQL component tries to convert the message body to an object of java.util.Iterator
type and then uses this iterator to fill the query parameters (where each query parameter is represented by a #
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 java.util.List
, the first item in the list is substituted into the first occurrence of #
in the SQL query, the second item in the list is substituted into the second occurrence of #
, and so on.
If batch
is set 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.
Result of the query
For select
operations, the result is an instance of List<Map<String, Object>>
type, as returned by the JdbcTemplate.queryForList() method. For update
operations, the result is the number of updated rows, returned as an Integer
.
Header values
When performing update
operations, the SQL Component stores the update count in the following message headers:
Header |
Description |
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The number of rows updated for |
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The number of rows returned for |
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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 |
Configuration
You can now set a reference to a DataSource
in the URI directly:
sql:select * from table where id=# order by name?dataSourceRef=myDS
Sample
In the sample below we execute a query and retrieve the result as a List
of rows, where each row is a Map<String, 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:
The SQL script createAndPopulateDatabase.sql
we execute looks like as described below:
Then we configure our route and our sql
component. Notice that we use a direct
endpoint in front of the sql
endpoint. This allows us to send an exchange to the direct
endpoint with the URI, direct:simple
, which is much easier for the client to use than the long sql:
URI. Note that the DataSource
is looked up up in the registry, so we can use standard Spring XML to configure our DataSource
.
And then we fire the message into the direct
endpoint that will route it to our sql
component that queries the database.
We could configure the DataSource
in Spring XML as follows:
<jee:jndi-lookup id="myDS" jndi-name="jdbc/myDataSource"/>
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 Camel 2.7, we use the following schema:
CREATE TABLE CAMEL_MESSAGEPROCESSED ( processorName VARCHAR(255), messageId VARCHAR(100) )
In Camel 2.8, we added the createdAt column:
CREATE TABLE CAMEL_MESSAGEPROCESSED ( processorName VARCHAR(255), messageId VARCHAR(100), createdAt 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 the spring XML file:
And finally we can create our JDBC idempotent repository in the spring XML file as well:
Customize the JdbcMessageIdRepository
Starting with Camel 2.9.1 you have a few options to tune the org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository
for your needs:
Parameter |
Default Value |
Description |
---|---|---|
createTableIfNotExists |
true |
Defines whether or not Camel should try to create the table if it doesn't exist. |
tableExistsString |
SELECT 1 FROM CAMEL_MESSAGEPROCESSED WHERE 1 = 0 |
This 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. |
queryString |
SELECT 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 ( |
insertString |
INSERT 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 ( |
deleteString |
DELETE 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 ( |
A customized org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository
could look like:
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 AggregationRepository
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 AggregationRepository
.
The JdbcAggregationRepository
allows together with Camel to provide persistent support for the Aggregator.
It has the following options:
Option |
Type |
Description |
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Mandatory: The |
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Mandatory: The name of the repository. |
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Mandatory: The |
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A |
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boolean |
Whether the get operation should return the old existing Exchange if any existed. By default this option is |
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boolean |
Whether or not recovery is enabled. This option is by default |
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long |
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. |
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int |
Allows 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 |
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String |
An endpoint uri for a Dead Letter Channel where exhausted recovered Exchanges will be moved. If this option is used then the |
What is preserved when persisting
JdbcAggregationRepository
will only preserve any Serializable
compatible data types. If a data type is not such a type its dropped and a WARN
is logged. And it only persists the Message
body and the Message
headers. The Exchange
properties are not persisted.
Recovery
The JdbcAggregationRepository
will by default recover any failed Exchange. It does this by having a background tasks that scans for failed Exchanges in the persistent store. You can use the checkInterval
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 Exchange. Any Exchange 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 Exchange is being recovered/redelivered:
Header |
Type |
Description |
---|---|---|
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Boolean |
Is set to true to indicate the Exchange is being redelivered. |
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Integer |
The redelivery attempt, starting from 1. |
Only when an Exchange has been successfully processed it will be marked as complete which happens when the confirm
method is invoked on the AggregationRepository
. This means if the same Exchange fails again it will be kept retried until it success.
You can use option maximumRedeliveries
to limit the maximum number of redelivery attempts for a given recovered Exchange. You must also set the deadLetterUri
option so Camel knows where to send the Exchange when the maximumRedeliveries
was hit.
You can see some examples in the unit tests of camel-sql, for 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 "_COMPLETED"
. The name must be configured in the Spring bean with the RepositoryName
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 id field does not have the same content depending on the table.
In the aggregation table id holds the correlation Id used by the component to aggregate the messages. In the completed table, id holds the id of the exchange stored in corresponding the blob field.
Here is the SQL query used to create the tables, just replace "aggregation"
with your aggregator repository name.
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) );
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 JdbcCodec
class. One detail of the code requires your attention: the ClassLoadingAwareObjectInputStream
.
The ClassLoadingAwareObjectInputStream
has been reused from the Apache ActiveMQ project. It wraps an ObjectInputStream
and use it with the ContextClassLoader
rather than the currentThread
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 PlatformTransactionManager
is required to orchestrate transaction.
Service (Start/Stop)
The start
method verify the connection of the database and the presence of the required tables. If anything is wrong it will fail during starting.
Aggregator configuration
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 lobHandler
property.
Here is the declaration for Oracle:
<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>