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Chapter 21. JSonPath

Overview
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The JSonPath language provides a convenient syntax for extracting portions of a JSon message. The syntax of JSon is similar to XPath, but it is used to extract JSon objects from a JSon message, instead of acting on XML. The jsonpath DSL command can be used either as an expression or as a predicate (where an empty result gets interpreted as boolean false).

Adding the JSonPath package
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To use JSonPath in your Camel routes, you need to add a dependency on camel-jsonpath to your project, as follows: 
<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-jsonpath</artifactId>
  <version>${camel-version}</version>
</dependency>
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Java example
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The following Java example shows how to use the jsonpath() DSL command to select items in a certain price range: 
from("queue:books.new")
  .choice()
    .when().jsonpath("$.store.book[?(@.price < 10)]")
      .to("jms:queue:book.cheap")
    .when().jsonpath("$.store.book[?(@.price < 30)]")
      .to("jms:queue:book.average")
    .otherwise()
      .to("jms:queue:book.expensive")
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If the JSonPath query returns an empty set, the result is interpreted as false. In this way, you can use a JSonPath query as a predicate.

XML example
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The following XML example shows how to use the jsonpath DSL element to define predicates in a route: 
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
  <route>
    <from uri="direct:start"/>
    <choice>
      <when>
        <jsonpath>$.store.book[?(@.price &lt; 10)]</jsonpath>
        <to uri="mock:cheap"/>
      </when>
      <when>
        <jsonpath>$.store.book[?(@.price &lt; 30)]</jsonpath>
        <to uri="mock:average"/>
      </when>
      <otherwise>
        <to uri="mock:expensive"/>
      </otherwise>
    </choice>
  </route>
</camelContext>
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Suppress Exceptions
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JSonPath will throw an exception if the path configured by the jsonpath expression is not found. The exception can be ignored by setting the SuppressExceptions option to true. For example, in the code below, adding the true option as part of the jsonpath parameters: 
from("direct:start")
    .choice()
        // use true to suppress exceptions
        .when().jsonpath("person.middlename", true)
            .to("mock:middle")
        .otherwise()
            .to("mock:other");
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In XML DSL use the following syntax: 
<route>
  <from uri="direct:start"/>
  <choice>
    <when>
      <jsonpath suppressExceptions="true">person.middlename</jsonpath>
      <to uri="mock:middle"/>
    </when>
    <otherwise>
      <to uri="mock:other"/>
    </otherwise>
  </choice>
</route>
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JSonPath injection
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When using bean integration to invoke a bean method, you can use JSonPath to extract a value from the message and bind it to a method parameter. For example: 
// Java
public class Foo {
     
    @Consume(uri = "activemq:queue:books.new")
    public void doSomething(@JsonPath("$.store.book[*].author") String author, @Body String json) {
      // process the inbound message here
    }
}
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Integrating Jackson with Camel TypeConverters
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The camel-jackson module allows to integrate Jackson as a Type Converter in the Camel Registry. You need to explicitly enable the camel-jackson by setting the CamelContext properties, as shown below: 
// enable Jackson json type converter
getContext().getProperties().put("CamelJacksonEnableTypeConverter", "true");
// allow Jackson json to convert to pojo types also (by default jackson only converts to String and other simple types)
getContext().getProperties().put("CamelJacksonTypeConverterToPojo", "true");
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The camel-jackson type converter integrates with JAXB. You can annotate POJO class with JAXB annotations that Jackson can leverage.

Reference
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For more details about JSonPath, see the JSonPath project page.
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