Upgrading to switch from JSON/XML marshalling in order to use Jackson 2 - spring

Question

I am currently using Spring - and am using Jersey's old technologies to marshall and unmarshall - I need to upgrade the marshalling library to the latest version in order to use Jackson.
I have usually got some code to show, but obviously in this scenario - I am not even sure where to begin, so if anyone can help out that would be cool.
WEB.XML CONFIGURATION FOR JERSEY :
<servlet>
<description>Jersey Servlet</description>
<servlet-name>jersey</servlet-name>
<servlet-class>com.sun.jersey.spi.spring.container.servlet.SpringServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
POM :
<jersey.version>1.4</jersey.version>
<dependency>
<groupId>com.sun.jersey.contribs</groupId>
<artifactId>jersey-spring</artifactId>
<version>${jersey.version}</version>
<scope>runtime</scope>
<!-- exclude spring dependencies so can pin to our desired versions (esp. spring-web) -->
<exclusions>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring</artifactId>
</exclusion>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
</exclusion>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
</exclusion>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
</exclusion>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
</exclusion>
<exclusion>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>com.sun.jersey</groupId>
<artifactId>jersey-json</artifactId>
<version>${jersey.version}</version>
</dependency>
<dependency>
<groupId>com.sun.jersey</groupId>
<artifactId>jersey-server</artifactId>
<version>${jersey.version}</version>
</dependency>

Answer 1

If you want to use Jackson 2, you should first get rid of the jersey-json, then add the following
<dependency>
<groupId>com.fasterxml.jackson.jaxrs</groupId>
<artifactId>jackson-jaxrs-json-provider</artifactId>
<version>${jackson2.version}</version>
<!-- latest right now is 2.8.3 -->
</dependency>
Then in your servlet configuration, add the Jackson package to the list of packages to scan.
<servlet>
<servlet-name>jersey</servlet-name>
<servlet-class>com.sun.jersey.spi.spring.container.servlet.SpringServlet</servlet-class>
<init-param>
<param-name>com.sun.jersey.config.property.packages</param-name>
<param-value>
your.packages,
com.fasterxml.jackson.jaxrs.json <!-- add jackson -->
</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
Note that if you are using a Jackson version newer than 2.7.0, the above package will not include the Jackson ExceptionMappers. According to this issue, it seems they are now removed and also the #Provider annotations have been removed. So we can't package scan for them.
So if you do want the mappers, you should declare them by class.
<param-name>
com.sun.jersey.config.property.classnames
</param-name>
<param-value>
com.fasterxml.jackson.jaxrs.base.JsonMappingExceptionMapper,
com.fasterxml.jackson.jaxrs.base.JsonParseExceptionMapper
</param-value>
I should mention though, that it's really recommended to write your own mappers. The response the these mappers spit out, is the exception message, and that's not really something you want as the error response.

Answer 2

You will need to update your POM to include the jackson jars(core, databind, annotaion) in https://mvnrepository.com/artifact/com.fasterxml.jackson.core. You will also need to do the below for converting JSON to Java object and vice versa
<beans:bean
class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
<beans:property name="messageConverters">
<beans:list>
<beans:ref bean="jsonMessageConverter" />
</beans:list>
</beans:property>
</beans:bean>
<!-- Configure bean to convert JSON to POJO and vice versa -->
<beans:bean id="jsonMessageConverter"
class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
</beans:bean>
You would need to create a class with variables that are named after the "keys" in JSON. The code to convert JSON string to object of the JAVA class would be as below:
Suppose JSON is
{
'name' : 'Test',
'userId' : 'test101'
}
The Java class corresponding to this would be:
public class Test {
private String name;
private String userId;
// Write getter and setter methods for each variable.
}
The code for converting JSON string to the object of Test class would be:
ObjectMapper mapper = new ObjectMapper();
String jsonInString = ""{'name' : 'Test', 'userId' : 'test101'}"";
//JSON from String to Object
Test obj = mapper.readValue(jsonInString, Test.class);
obj.getName() would give value corresponding to the key.