How to access array elements in body of Camel message

user_1303051 0
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My Camel route is calling a REST service, which returns a JSON string. Problem is that the JSON is not an object but an array of objects, i.e.:

[
  { object_1 },
  { object_2 }
]

First, I want to figure out if this array is empty, as an expression in a choice-when statement:

.choice()
  .when( <array-is-empty-expression> )
    ...
  .otherwise()
    ...

As a solution I used an expression .when("${body} == '[ ]'") which works fine but it doesn't give me the flexibility to find out how many elements there are in the array (well, just that there are 0 or more than 0). So I would really like something like .when("${body expression} == 0").

Secondly, I want to have an expression that assigns a property of, for example, the second object from the JSON array, to set a header property. For example, .header("To", expression).

Can anyone help me with these expressions?

apache-camel
1 Answers

The best approach is to unmarshal your Json string to get a list of objects. Then you can invoke size() method to get the number of elements in your list. Finally, you can access any element of the list using [] operator:

        from("file://C:/q69164959/test")
        .unmarshal().json(JsonLibrary.Jackson)
        .setHeader("To", simple("Default"))
        .choice()
        .when(simple("${body.size()} == 0" ))
        .to("log:org.orzowei.so.question.q69164959?level=ERROR")
        .otherwise()
        .setHeader("To", simple("${body[0][a]}"))
        .to("log:org.orzowei.so.question.q69164959?level=WARN")
        .end()
        .log(LoggingLevel.INFO, "header.To == ${header.To}")

Using [] as input, you can see this log output:

2021-09-13 23:41:49.830 ERROR 32028 --- [/q69076203/test] org.orzowei.so.question.q69164959        : Exchange[ExchangePattern: InOnly, BodyType: java.util.ArrayList, Body: ]
2021-09-13 23:41:49.830  INFO 32028 --- [/q69076203/test] route1                                   : header.To == Default

Using [{a=1, b=2}, {a=3, b=4}] as input, you can see this log output:

2021-09-13 23:42:01.161  WARN 32028 --- [/q69076203/test] org.orzowei.so.question.q69164959        : Exchange[ExchangePattern: InOnly, BodyType: java.util.ArrayList, Body: [{a=1, b=2}, {a=3, b=4}]]
2021-09-13 23:42:01.161  INFO 32028 --- [/q69076203/test] route1                                   : header.To == 1
user_21654470
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