Java tutorial
/* * Copyright 2002-2014 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.http.converter.json; import java.io.IOException; import java.lang.reflect.Type; import java.nio.charset.Charset; import java.util.List; import org.springframework.http.HttpInputMessage; import org.springframework.http.HttpOutputMessage; import org.springframework.http.MediaType; import org.springframework.http.converter.AbstractHttpMessageConverter; import org.springframework.http.converter.GenericHttpMessageConverter; import org.springframework.http.converter.HttpMessageNotReadableException; import org.springframework.http.converter.HttpMessageNotWritableException; import org.springframework.util.Assert; import com.fasterxml.jackson.core.JsonEncoding; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.core.util.DefaultPrettyPrinter; import com.fasterxml.jackson.databind.JavaType; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.SerializationFeature; /** * Implementation of {@link org.springframework.http.converter.HttpMessageConverter HttpMessageConverter} * that can read and write JSON using <a href="http://jackson.codehaus.org/">Jackson 2's</a> {@link ObjectMapper}. * * <p>This converter can be used to bind to typed beans, or untyped {@link java.util.HashMap HashMap} instances. * * <p>By default, this converter supports {@code application/json}. This can be overridden by setting the * {@link #setSupportedMediaTypes(List) supportedMediaTypes} property. * * <p>Tested against Jackson 2.3; compatible with Jackson 2.0 and higher. Note that tests failed with Jackson 2.4 * on Android 2.2 (API Level 8) and older versions. Jackson 2.4 uses APIs not available on those platforms. * * @author Arjen Poutsma * @author Keith Donald * @author Rossen Stoyanchev * @author Roy Clarkson * @since 1.0.1 */ public class MappingJackson2HttpMessageConverter extends AbstractHttpMessageConverter<Object> implements GenericHttpMessageConverter<Object> { public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8"); private ObjectMapper objectMapper = new ObjectMapper(); private String jsonPrefix; private Boolean prettyPrint; /** * Construct a new {@code MappingJackson2HttpMessageConverter}. */ public MappingJackson2HttpMessageConverter() { super(new MediaType("application", "json", DEFAULT_CHARSET), new MediaType("application", "*+json", DEFAULT_CHARSET)); } /** * Set the {@code ObjectMapper} for this view. If not set, a default * {@link ObjectMapper#ObjectMapper() ObjectMapper} is used. * <p>Setting a custom-configured {@code ObjectMapper} is one way to take further control of the JSON * serialization process. For example, an extended {@link org.codehaus.jackson.map.SerializerFactory} * can be configured that provides custom serializers for specific types. The other option for refining * the serialization process is to use Jackson's provided annotations on the types to be serialized, * in which case a custom-configured ObjectMapper is unnecessary. */ public void setObjectMapper(ObjectMapper objectMapper) { Assert.notNull(objectMapper, "ObjectMapper must not be null"); this.objectMapper = objectMapper; configurePrettyPrint(); } private void configurePrettyPrint() { if (this.prettyPrint != null) { this.objectMapper.configure(SerializationFeature.INDENT_OUTPUT, this.prettyPrint); } } /** * Return the underlying {@code ObjectMapper} for this view. */ public ObjectMapper getObjectMapper() { return this.objectMapper; } /** * 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; } /** * Indicate whether the JSON output by this view should be prefixed with "{} &&". Default is 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 does not affect the evaluation of JSON, but if JSON validation is performed on the * string, the prefix would need to be ignored. * @see #setJsonPrefix */ public void setPrefixJson(boolean prefixJson) { this.jsonPrefix = (prefixJson ? "{} && " : null); } /** * Whether to use the {@link DefaultPrettyPrinter} when writing JSON. * This is a shortcut for setting up an {@code ObjectMapper} as follows: * <pre> * ObjectMapper mapper = new ObjectMapper(); * mapper.configure(SerializationFeature.INDENT_OUTPUT, true); * converter.setObjectMapper(mapper); * </pre> */ public void setPrettyPrint(boolean prettyPrint) { this.prettyPrint = prettyPrint; configurePrettyPrint(); } @Override public boolean canRead(Class<?> clazz, MediaType mediaType) { return canRead(clazz, null, mediaType); } public boolean canRead(Type type, Class<?> contextClass, MediaType mediaType) { JavaType javaType = getJavaType(type, contextClass); return (this.objectMapper.canDeserialize(javaType) && canRead(mediaType)); } @Override public boolean canWrite(Class<?> clazz, MediaType mediaType) { return (this.objectMapper.canSerialize(clazz) && canWrite(mediaType)); } @Override protected boolean supports(Class<?> clazz) { // should not be called, since we override canRead/Write instead throw new UnsupportedOperationException(); } @Override protected Object readInternal(Class<?> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException { JavaType javaType = getJavaType(clazz, null); return readJavaType(javaType, inputMessage); } public Object read(Type type, Class<?> contextClass, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException { JavaType javaType = getJavaType(type, contextClass); return readJavaType(javaType, inputMessage); } private Object readJavaType(JavaType javaType, HttpInputMessage inputMessage) { try { return this.objectMapper.readValue(inputMessage.getBody(), javaType); } catch (IOException ex) { throw new HttpMessageNotReadableException("Could not read JSON: " + ex.getMessage(), ex); } } @SuppressWarnings("deprecation") @Override protected void writeInternal(Object object, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException { JsonEncoding encoding = getJsonEncoding(outputMessage.getHeaders().getContentType()); JsonGenerator jsonGenerator = this.objectMapper.getJsonFactory() .createJsonGenerator(outputMessage.getBody(), encoding); // A workaround for JsonGenerators not applying serialization features // https://github.com/FasterXML/jackson-databind/issues/12 if (this.objectMapper.isEnabled(SerializationFeature.INDENT_OUTPUT)) { jsonGenerator.useDefaultPrettyPrinter(); } try { if (this.jsonPrefix != null) { jsonGenerator.writeRaw(this.jsonPrefix); } this.objectMapper.writeValue(jsonGenerator, object); } catch (JsonProcessingException ex) { throw new HttpMessageNotWritableException("Could not write JSON: " + ex.getMessage(), ex); } } /** * Return the Jackson {@link JavaType} for the specified type and context class. * <p>The default implementation returns {@link ObjectMapper#constructType(java.lang.reflect.Type)} * or {@code ObjectMapper.getTypeFactory().constructType(type, contextClass)}, * but this can be overridden in subclasses, to allow for custom generic collection handling. * For instance: * <pre class="code"> * protected JavaType getJavaType(Type type) { * if (type instanceof Class && List.class.isAssignableFrom((Class)type)) { * return TypeFactory.collectionType(ArrayList.class, MyBean.class); * } else { * return super.getJavaType(type); * } * } * </pre> * @param type the type to return the java type for * @param contextClass a context class for the target type, for example a class * in which the target type appears in a method signature, can be {@code null} * signature, can be {@code null} * @return the java type */ protected JavaType getJavaType(Type type, Class<?> contextClass) { return (contextClass != null) ? this.objectMapper.getTypeFactory().constructType(type, contextClass) : this.objectMapper.constructType(type); } /** * Determine the JSON encoding to use for the given content type. * @param contentType the media type as requested by the caller * @return the JSON encoding to use (never {@code null}) */ protected JsonEncoding getJsonEncoding(MediaType contentType) { if (contentType != null && contentType.getCharSet() != null) { Charset charset = contentType.getCharSet(); for (JsonEncoding encoding : JsonEncoding.values()) { if (charset.name().equals(encoding.getJavaName())) { return encoding; } } } return JsonEncoding.UTF8; } }