Chapter 21. JsonPath

Overview

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

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>

Java example

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")

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

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>$.store.book[?(@.price < 10)]</jsonpath>
        <to uri="mock:cheap"/>
      </when>
      <when>
        <jsonpath>$.store.book[?(@.price < 30)]</jsonpath>
        <to uri="mock:average"/>
      </when>
      <otherwise>
        <to uri="mock:expensive"/>
      </otherwise>
    </choice>
  </route>
</camelContext>

Easy Syntax

When you wish to define a basic predicate using jsonpath syntax it can be a bit hard to remember the syntax. For example, to find out all the cheap books, you have to write the syntax as follows:

$.store.book[?(@.price < 20)]

However, what if you could just write it as:

store.book.price < 20

You can also omit the path if you just want to look at nodes with a price key:

price < 20

To support this, there is a EasyPredicateParser which you use to define the predicate using a basic style. That means the predicate must not start with the $ sign, and must include only one operator. The easy syntax is as follows:

left OP right

You can use Camel simple language in the right operator, for example,

store.book.price < ${header.limit}

Supported Message Body Types

Camel JSonPath supports message body using the following types:

TypeDescription

File

Reading from files

String

Plain strings

Map

essage body as java.util.Map type

List

Message body as java.util.List type

POJO

Optional If Jackson is on the classpath, then camel-jsonpath is able to use Jackson to read the message body as POJO and convert to java.util.Map which is supported by JSonPath. For example you can add camel-jackson as dependency to include Jackson.

InputStream

If none of the above types matches, then Camel will attempt to read the message body as an java.io.InputStream.

If a message body is of unsupported type then an exception is thrown by default, however you can configure JSonPath to suppress exceptions.

Suppress Exceptions

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");

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>

JsonPath injection

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
    }
}

Inline Simple Expressions

New in Camel 2.18.

Camel supports inline Simple expressions in the JsonPath expressions. The Simple language insertions must be expressed in Simple syntax as shown below:

from("direct:start")
  .choice()
    .when().jsonpath("$.store.book[?(@.price < `${header.cheap}`)]")
      .to("mock:cheap")
    .when().jsonpath("$.store.book[?(@.price < `${header.average}`)]")
      .to("mock:average")
    .otherwise()
      .to("mock:expensive");

Turn off support for Simple expressions by setting the option allowSimple=false as shown below.

Java:

// Java DSL
.when().jsonpath("$.store.book[?(@.price < 10)]", `false, false`)

XML DSL:

// XML DSL
<jsonpath allowSimple="false">$.store.book[?(@.price &lt; 10)]</jsonpath>

Reference

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