/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.view.json;

import java.io.IOException;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

import com.fasterxml.jackson.annotation.JsonView;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ser.FilterProvider;

import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
import org.springframework.validation.BindingResult;
import org.springframework.web.servlet.View;

Spring MVC View that renders JSON content by serializing the model for the current request using Jackson 2's ObjectMapper. 
By default, the entire contents of the model map (with the exception of framework-specific classes) will be encoded as JSON. If the model contains only one key, you can have it extracted encoded as JSON alone via setExtractValueFromSingleKeyModel. 
The default constructor uses the default configuration provided by Jackson2ObjectMapperBuilder. 
Compatible with Jackson 2.6 and higher, as of Spring 4.3.
Author:
Jeremy Grelle, Arjen Poutsma, Rossen Stoyanchev, Juergen Hoeller, Sebastien Deleuze
Since:
3.1.2/**
 * Spring MVC {@link View} that renders JSON content by serializing the model for the current request
 * using <a href="http://wiki.fasterxml.com/JacksonHome">Jackson 2's</a> {@link ObjectMapper}.
 *
 * <p>By default, the entire contents of the model map (with the exception of framework-specific classes)
 * will be encoded as JSON. If the model contains only one key, you can have it extracted encoded as JSON
 * alone via  {@link #setExtractValueFromSingleKeyModel}.
 *
 * <p>The default constructor uses the default configuration provided by {@link Jackson2ObjectMapperBuilder}.
 *
 * <p>Compatible with Jackson 2.6 and higher, as of Spring 4.3.
 *
 * @author Jeremy Grelle
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @author Sebastien Deleuze
 * @since 3.1.2
 */
public class MappingJackson2JsonView extends AbstractJackson2View {

	
Default content type: "application/json". Overridable through AbstractView.setContentType. /**
	 * Default content type: "application/json".
	 * Overridable through {@link #setContentType}.
	 */
	public static final String DEFAULT_CONTENT_TYPE = "application/json";

	@Nullable
	private String jsonPrefix;

	@Nullable
	private Set<String> modelKeys;

	private boolean extractValueFromSingleKeyModel = false;


	
Construct a new MappingJackson2JsonView using default configuration provided by Jackson2ObjectMapperBuilder and setting the content type to application/json. /**
	 * Construct a new {@code MappingJackson2JsonView} using default configuration
	 * provided by {@link Jackson2ObjectMapperBuilder} and setting the content type
	 * to {@code application/json}.
	 */
	public MappingJackson2JsonView() {
		super(Jackson2ObjectMapperBuilder.json().build(), DEFAULT_CONTENT_TYPE);
	}

	
Construct a new MappingJackson2JsonView using the provided ObjectMapper and setting the content type to application/json. 
Since:
4.2.1/**
	 * Construct a new {@code MappingJackson2JsonView} using the provided
	 * {@link ObjectMapper} and setting the content type to {@code application/json}.
	 * @since 4.2.1
	 */
	public MappingJackson2JsonView(ObjectMapper objectMapper) {
		super(objectMapper, DEFAULT_CONTENT_TYPE);
	}


	
Specify a custom prefix to use for this view's JSON output.
Default is none.
See Also:
setPrefixJson/**
	 * Specify a custom prefix to use for this view's JSON output.
	 * Default is none.
	 * @see #setPrefixJson
	 */
	public void setJsonPrefix(String jsonPrefix) {
		this.jsonPrefix = jsonPrefix;
	}

	
Indicates whether the JSON output by this view should be prefixed with ")]}', ". Default is false. 
Prefixing the JSON string in this manner is used to help prevent JSON Hijacking.
The prefix renders the string syntactically invalid as a script so that it cannot be hijacked.
This prefix should be stripped before parsing the string as JSON.
See Also:
setJsonPrefix/**
	 * Indicates whether the JSON output by this view should be prefixed with <tt>")]}', "</tt>.
	 * Default is {@code false}.
	 * <p>Prefixing the JSON string in this manner is used to help prevent JSON Hijacking.
	 * The prefix renders the string syntactically invalid as a script so that it cannot be hijacked.
	 * This prefix should be stripped before parsing the string as JSON.
	 * @see #setJsonPrefix
	 */
	public void setPrefixJson(boolean prefixJson) {
		this.jsonPrefix = (prefixJson ? ")]}', " : null);
	}

	
{@inheritDoc}
/**
	 * {@inheritDoc}
	 */
	@Override
	public void setModelKey(String modelKey) {
		this.modelKeys = Collections.singleton(modelKey);
	}

	
Set the attributes in the model that should be rendered by this view.
When set, all other model attributes will be ignored.
/**
	 * Set the attributes in the model that should be rendered by this view.
	 * When set, all other model attributes will be ignored.
	 */
	public void setModelKeys(@Nullable Set<String> modelKeys) {
		this.modelKeys = modelKeys;
	}

	
Return the attributes in the model that should be rendered by this view.
/**
	 * Return the attributes in the model that should be rendered by this view.
	 */
	@Nullable
	public final Set<String> getModelKeys() {
		return this.modelKeys;
	}

	
Set whether to serialize models containing a single attribute as a map or
whether to extract the single value from the model and serialize it directly.
The effect of setting this flag is similar to using MappingJackson2HttpMessageConverter with an @ResponseBody request-handling method. 
Default is false. /**
	 * Set whether to serialize models containing a single attribute as a map or
	 * whether to extract the single value from the model and serialize it directly.
	 * <p>The effect of setting this flag is similar to using
	 * {@code MappingJackson2HttpMessageConverter} with an {@code @ResponseBody}
	 * request-handling method.
	 * <p>Default is {@code false}.
	 */
	public void setExtractValueFromSingleKeyModel(boolean extractValueFromSingleKeyModel) {
		this.extractValueFromSingleKeyModel = extractValueFromSingleKeyModel;
	}

	
Filter out undesired attributes from the given model. The return value can be either another Map or a single value object. 
The default implementation removes BindingResult instances and entries not included in the modelKeys property. 
Params:
model – the model, as passed on to AbstractJackson2View.renderMergedOutputModel
Returns:
the value to be rendered/**
	 * Filter out undesired attributes from the given model.
	 * The return value can be either another {@link Map} or a single value object.
	 * <p>The default implementation removes {@link BindingResult} instances and entries
	 * not included in the {@link #setModelKeys modelKeys} property.
	 * @param model the model, as passed on to {@link #renderMergedOutputModel}
	 * @return the value to be rendered
	 */
	@Override
	protected Object filterModel(Map<String, Object> model) {
		Map<String, Object> result = new HashMap<>(model.size());
		Set<String> modelKeys = (!CollectionUtils.isEmpty(this.modelKeys) ? this.modelKeys : model.keySet());
		model.forEach((clazz, value) -> {
			if (!(value instanceof BindingResult) && modelKeys.contains(clazz) &&
					!clazz.equals(JsonView.class.getName()) &&
					!clazz.equals(FilterProvider.class.getName())) {
				result.put(clazz, value);
			}
		});
		return (this.extractValueFromSingleKeyModel && result.size() == 1 ? result.values().iterator().next() : result);
	}

	@Override
	protected void writePrefix(JsonGenerator generator, Object object) throws IOException {
		if (this.jsonPrefix != null) {
			generator.writeRaw(this.jsonPrefix);
		}
	}

}