Un breve ejemplo de cómo utilizar la librería Jackson de Spring para consumir un JSON que retorna un servicio REST. La clase de abajo es un Singleton que inicializa el RestTemplate una sola vez.
import java.util.ArrayList;
import java.util.List;
import org.springframework.http.MediaType;
import org.springframework.http.client.CommonsClientHttpRequestFactory;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.json.MappingJacksonHttpMessageConverter;
import org.springframework.web.client.RestTemplate;
public class RestJsonTest {
private static RestJsonTest instance;
private RestTemplate restTemplate;
private String url ="http://rest.service.url";
public static RestJsonTest getInstance() {
if (instance == null) {
instance = new RestJsonTest();
}
return instance;
}
private RestJsonTest() {
// Setup the RestTemplate configuration.
restTemplate = new RestTemplate();
restTemplate.setRequestFactory(new CommonsClientHttpRequestFactory());
List<HttpMessageConverter<?>> messageConverterList = restTemplate.getMessageConverters();
// Set HTTP Message converter using a JSON implementation.
MappingJacksonHttpMessageConverter jsonMessageConverter = new MappingJacksonHttpMessageConverter();
// Add supported media type returned by BI API.
List<MediaType> supportedMediaTypes = new ArrayList<MediaType>();
supportedMediaTypes.add(new MediaType("text", "plain"));
supportedMediaTypes.add(new MediaType("application", "json"));
jsonMessageConverter.setSupportedMediaTypes(supportedMediaTypes);
messageConverterList.add(jsonMessageConverter);
restTemplate.setMessageConverters(messageConverterList);
}
public SearchResults searchResults() {
return restTemplate.getForObject(url, SearchResults.class);
}
public static void main(String[] args) {
RestJsonTest jsonTest = RestJsonTest.getInstance();
SearchResults results = jsonTest.searchResults();
}
}
El mapeo del JSON a clases Java se puede hacer por medio de anotaciones como se muestra a continuación.ç
package com.bodybuilding.api.commerce.clientservice;
import java.util.List;
import org.codehaus.jackson.annotate.JsonIgnoreProperties;
import org.codehaus.jackson.annotate.JsonProperty;
/**
*{
* "search_keywords":"Social Networks",
* "total_time":200,
* "results":{
* "result_01":{
* "url":"http://www.facebook.com",
* "rank": "1"
* },
* "result_02":{
* "url":"http://www.twitter.com",
* "rank": "2"
* }
* }
* }
*/
@JsonIgnoreProperties(ignoreUnknown=true)
public class SearchResults {
@JsonProperty("search_keywords")
private String keywords;
@JsonProperty("total_time")
private long totalTime;
@JsonProperty("results")
private List<SearchResult> results;
public String getKeywords() {
return keywords;
}
public void setKeywords(String keywords) {
this.keywords = keywords;
}
public long getTotalTime() {
return totalTime;
}
public void setTotalTime(long totalTime) {
this.totalTime = totalTime;
}
public List<SearchResult> getResults() {
return results;
}
public void setResults(List<SearchResult> results) {
this.results = results;
}
}
import org.codehaus.jackson.annotate.JsonIgnoreProperties;
import org.codehaus.jackson.annotate.JsonProperty;
@JsonIgnoreProperties(ignoreUnknown=true)
public class SearchResult {
@JsonProperty("url")
private String url;
@JsonProperty("rank")
private int rank;
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public int getRank() {
return rank;
}
public void setRank(int rank) {
this.rank = rank;
}
}
También se puede configurar el bean de RestTemplate por medio de una inyección de Spring:
<bean id="restTemplate" class="org.springframework.web.client.RestTemplate">
<property name="requestFactory">
<bean id="clientHttpRequestFactory" class="org.springframework.http.client.CommonsClientHttpRequestFactory" />
</property>
<property name="messageConverters">
<list>
<bean id="jsonMessageConverter" class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
<property name="supportedMediaTypes">
<list>
<bean id="jsonMediaTypeTextPlain" class="org.springframework.http.MediaType">
<constructor-arg value="text"/>
<constructor-arg value="plain"/>
</bean>
<bean id="jsonMediaTypeApplicationJson" class="org.springframework.http.MediaType">
<constructor-arg value="application"/>
<constructor-arg value="json"/>
</bean>
</list>
</property>
</bean>
</list>
</property>
</bean>
