What's the simpliest way for Jersey serialize HashMap to json in a restful service?

Question

There are lots of questions on returning serialized HashMap, but I didn't find a very good answer.

Now I just want to simply create a rest service like this:

@XmlElement(name = "Calibration")
private HashMap<String, Double> entry = new HashMap<String, Double>();

Then in my REST service:

@GET
@Produces(MediaType.APPLICATION_JSON)
@Path("/entry")
public HashMap<String, Double> current() {
    System.out.println("calibration request");
    entry.put("test", 3.00);
    return entry;
}

It throws javax.ws.rs.WebApplicationException when the service is called:

com.sun.jersey.api.MessageException: A message body writer for Java class java.util.HashMap, and Java type java.util.HashMap, and MIME media type application/json was not found.

My pom.xml, in case it is useful:

<dependency>
        <groupId>com.sun.grizzly</groupId>
        <artifactId>grizzly-servlet-webserver</artifactId>
        <version>1.9.18-i</version>
    </dependency>
    <dependency>
        <groupId>com.sun.grizzly</groupId>
        <artifactId>grizzly-comet-webserver</artifactId>
        <version>1.9.46</version>
    </dependency>
    <dependency>
        <groupId>com.sun.jersey</groupId>
        <artifactId>jersey-grizzly</artifactId>
        <version>1.9.1</version>
    </dependency>
    <dependency>
        <groupId>com.sun.jersey</groupId>
        <artifactId>jersey-json</artifactId>
        <version>1.9.1</version>
    </dependency>

I'm using Grizzly as webContainer.

Answer 1

Jackson would be probably the easiest choice here (and Jersey JSON module has Jackson support built-in). You can configure the POJO JSON support via web.xml or via configuration object (see POJO support ).

Note: The latest Jersey 1.x version is 1.17.1, consider using this version if it's possible for you.

Answer 2

最好的方法是将HashMap映射到一个简单的bean中，然后返回该bean，而不是HashMap。