SpringMVC已经大行其道。一般的，都是返回JSP视图。如果需要返回JSON格式，我们大都掌握了一些方法。
在ContentNegotiatingViewResolver之前，一般使用XmlViewResolver的location属性，手工编写一个视图专门处理Json类型，就是将返回的数据封装成Json输出。下面介绍该方案具体代码。
exam-servlet.xml：
<bean id="xmlViewResolver" class="org.springframework.web.servlet.view.XmlViewResolver">
<property name="order" value="1"/>
<property name="location" value="/WEB-INF/views.xml"/>
</bean>
<bean id="viewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="order" value="2"></property>
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
<property name="viewClass"
value="org.springframework.web.servlet.view.JstlView" />
</bean>
views.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="json" class="cc.monggo.web.views.JsonView"></bean>
</beans>
JsonView.java
/**
*
*/
package cc.monggo.web.views; import java.util.HashMap;
import java.util.Iterator;
import java.util.Map; import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse; import net.sf.json.JSON;
import net.sf.json.JSONArray;
import net.sf.json.JSONSerializer;
import net.sf.json.JsonConfig;
import net.sf.json.filters.OrPropertyFilter;
import net.sf.json.util.PropertyFilter; import org.springframework.web.servlet.view.AbstractView; import cc.monggo.web.form.BaseForm; /**
* @author fangjinsong
*
*/
public class JsonView extends AbstractView {
private static final String DEFAULT_JSON_CONTENT_TYPE = "application/json;charset=UTF-8";
private boolean forceTopLevelArray = false;
private boolean skipBindingResult = true;
private JsonConfig jsonConfig = new JsonConfig(); public JsonView() {
super();
setContentType(DEFAULT_JSON_CONTENT_TYPE);
} public boolean isForceTopLevelArray() {
return forceTopLevelArray;
} public void setForceTopLevelArray(boolean forceTopLevelArray) {
this.forceTopLevelArray = forceTopLevelArray;
} public boolean isSkipBindingResult() {
return skipBindingResult;
} public void setSkipBindingResult(boolean skipBindingResult) {
this.skipBindingResult = skipBindingResult;
} public JsonConfig getJsonConfig() {
return jsonConfig;
} public void setJsonConfig(JsonConfig jsonConfig) {
this.jsonConfig = jsonConfig != null ? jsonConfig : new JsonConfig();
if (skipBindingResult) {
PropertyFilter jsonPropertyFilter = this.jsonConfig.getJavaPropertyFilter();
if (jsonPropertyFilter == null) {
this.jsonConfig.setJsonPropertyFilter(new BindingResultPropertyFilter());
} else {
this.jsonConfig.setJsonPropertyFilter(new OrPropertyFilter(new BindingResultPropertyFilter(), jsonPropertyFilter));
}
}
} public static String getDefaultJsonContentType() {
return DEFAULT_JSON_CONTENT_TYPE;
} public boolean isIgnoreDefaultExcludes() {
return getJsonConfig().isIgnoreDefaultExcludes();
} public void setExcludedProperties(String[] excludedProperties) {
jsonConfig.setExcludes(excludedProperties);
} public void setIgnoreDefaultExcludes(boolean ignoreDefaultExcludes) {
jsonConfig.setIgnoreDefaultExcludes(ignoreDefaultExcludes);
} protected String[] getExcludedProperties() {
return jsonConfig.getExcludes();
} @Override
protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
response.setContentType(getContentType());
Map newModel = new HashMap();
for (Iterator it = model.keySet().iterator(); it.hasNext();) {
Object key = it.next();
Object value = model.get(key);
if (!(value instanceof BaseForm)) {
newModel.put(key, value);
}
}
writeJSON(newModel, request, response);
} protected void writeJSON(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
JSON json = createJSON(model, request, response);
if (forceTopLevelArray) {
json = new JSONArray().element(json);
}
json.write(response.getWriter());
} protected final JSON defaultCreateJSON(Map model) {
if (skipBindingResult && jsonConfig.getJavaPropertyFilter() == null) {
jsonConfig.setJsonPropertyFilter(new BindingResultPropertyFilter());
}
return JSONSerializer.toJSON(model, jsonConfig);
} private JSON createJSON(Map model, HttpServletRequest request, HttpServletResponse response) {
return defaultCreateJSON(model);
} private static class BindingResultPropertyFilter implements PropertyFilter {
@Override
public boolean apply(Object source, String name, Object value) {
return name.startsWith("org.springframework.validation.BindingResult");
}
} }
这种方案会增加一个views.xml文件。另一个方案使用ContentNegotiatingViewResolver内容协商解析器。该解析器可以解析多种Controller返回结果，方法是分派给其他的解析器解析。这样就可以返回JSP视图，Xml视图，Json视图。其中Json视图由MappingJacksonJsonView视图表示。ContentNegotiatingViewResolver的一般配置如下：
<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
<property name="order" value="1" />
<property name="ignoreAcceptHeader" value="true" />
<property name="favorParameter" value="false" />
<property name="defaultContentType" value="text/html" />
<property name="mediaTypes">
<map>
<entry key="json" value="application/json" />
</map>
</property>
<property name="viewResolvers">
<list>
<bean class="org.springframework.web.servlet.view.BeanNameViewResolver" />
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView" />
<property name="prefix" value="/WEB-INF/jsp/" />
<property name="suffix" value=".jsp"></property>
</bean>
</list>
</property>
<property name="defaultViews">
<list>
<bean id="json" class="com.mogee.web.views.MogeeMappingJacksonJsonView" />
</list>
</property>
</bean>
要返回Json格式数据，Controller中一般使用JsonResult，@responseBody等技术。例如：
@RequestMapping("/json3.json")
public JsonResult testJson3(@RequestBody User u){
log.info("handle json output from ContentNegotiatingViewResolver");
return new JsonResult(true,"return ok");
}
这样一来，有一个问题：Controller总是返回Object对象，不能返回ModelAndview类型。按笔者的经验，经常有这样的需求：一个请求，如果返回了正确的结果，返回正常的JSP；如果返回了错误的结果，我们希望返回Json类型数据。为了满足这样要求，一般使用response.getWriter.print("")技术。笔者并不喜欢这样写法，不像Spring的风格。所以下面笔者将提出第二种方案。两者都能兼顾。Contoller代码如下。
@RequestMapping(value = "/test", method = RequestMethod.GET)
public ModelAndView jsonView(HttpServletRequest request, HttpServletResponse response, HelloForm form)
throws Exception {
Map<String, Object> map = new HashMap<String, Object>();
map.put("hello", "Hello");
ModelAndView mv = new ModelAndView(new MappingJacksonJsonView(), map);
return mv;
}
通过这样的代码，可以在Controller中灵活控制，返回JSON或者JSP都可以。看似完美的方案，也有一个问题，返回的时候会将Form也打包到Json中去。如下：
原因是因为MappingJacksonJsonView代码中将数据map，mv.add()，还有form，还有错误提示等四项数据都加入Json，原程序只是过滤了错误提示，所以就留下了form数据。
为此我们需要重写MappingJacksonJsonView，将剩余三种数据中的form也过滤掉。一般的，form都会继承BaseForm，所以只要使用instanceof判断即可。这样的改造简洁明了，符合Spring编程的特点。具体代码如下：
public class MogeeMappingJacksonJsonView extends MappingJacksonJsonView {
@Override
protected Object filterModel(Map<String, Object> model) {
Map<String, Object> result = new HashMap<String, Object>(model.size());
Set<String> renderedAttributes = !CollectionUtils.isEmpty(super.getRenderedAttributes()) ? super
.getRenderedAttributes() : model.keySet();
for (Map.Entry<String, Object> entry : model.entrySet()) {
if (!(entry.getValue() instanceof BindingResult) && renderedAttributes.contains(entry.getKey())) {
if (!(entry.getValue() instanceof BaseForm)) {
result.put(entry.getKey(), entry.getValue());
}
}
}
return result;
}
}
相应的，exam-servlet.xml中也要修改，代码如下：
如此，就完成了输出Json的方案。
方劲松 东莞虎门信丰物流
2015.3.20