GsonHttpMessageConverterForSpring3.java

/*
 * Copyright 2002-2011 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.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.lang.reflect.Type;
import java.nio.charset.Charset;

import org.springframework.http.HttpHeaders;
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.HttpMessageNotReadableException;
import org.springframework.http.converter.HttpMessageNotWritableException;
import org.springframework.util.Assert;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonIOException;
import com.google.gson.JsonParseException;
import com.google.gson.JsonSyntaxException;

/**
 * CHRISTIAN KLOCK, 2014.09.16
 * Class is left as obtained from
 * http://grepcode.com/file_/repo1.maven.org/maven2/org.springframework.android/spring-android-rest-template/1.0.1.RELEASE/org/springframework/http/converter/json/GsonHttpMessageConverter.java/?v=source
 *
 *
 * ERKO HANSAR, 2015.04.29
 * Renamed the file from GsonHttpMessageConverter to GsonHttpMessageConverterForSpring3 to avoid name clashing with Spring 4, which now includes a GsonHttpMessageConverter.
 * TODO: When TWE upgrades to Spring 4, start using the Spring included version.
 *
 *
 * @author Roy Clarkson
 * @since 1.0
 */
public class GsonHttpMessageConverterForSpring3 extends AbstractHttpMessageConverter<Object>{

    public static final Charset DEFAULT_CHARSET = Charset.forName( "UTF-8" );

    private Gson gson;

    private Type type = null;

    private boolean prefixJson = false;

    /**
     * Construct a new {@code GsonHttpMessageConverter} with a default {@link Gson#Gson() Gson}.
     */
    public GsonHttpMessageConverterForSpring3(){
        this( new Gson() );
    }

    /**
     * Construct a new {@code GsonHttpMessageConverter}.
     *
     * @param serializeNulls true to generate json for null values
     */
    public GsonHttpMessageConverterForSpring3( boolean serializeNulls ){
        this( serializeNulls ? new GsonBuilder().serializeNulls().create() : new Gson() );
    }

    /**
     * Construct a new {@code GsonHttpMessageConverter}.
     *
     * @param gson a customized {@link Gson#Gson() Gson}
     */
    public GsonHttpMessageConverterForSpring3( Gson gson ){
        super( new MediaType( "application", "json", DEFAULT_CHARSET ) );
        setGson( gson );
    }

    /**
     * Sets the {@code Gson} for this view. If not set, a default
     * {@link Gson#Gson() Gson} is used.
     * <p>Setting a custom-configured {@code Gson} is one way to take further control of the JSON serialization
     * process.
     * @throws IllegalArgumentException if gson is null
     */
    public void setGson( Gson gson ){
        Assert.notNull( gson, "'gson' must not be null" );
        this.gson = gson;
    }

    public void setType( Type type ){
        this.type = type;
    }

    public Type getType(){
        return type;
    }

    /**
     * Indicates 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.
     */
    public void setPrefixJson( boolean prefixJson ){
        this.prefixJson = prefixJson;
    }

    @Override
    public boolean canRead( Class<?> clazz, MediaType mediaType ){
        return canRead( mediaType );
    }

    @Override
    public boolean canWrite( Class<?> clazz, MediaType mediaType ){
        return 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{

        Reader json = new InputStreamReader( inputMessage.getBody(), getCharset( inputMessage.getHeaders() ) );

        try{
            Type typeOfT = getType();
            if( typeOfT != null ){
                return this.gson.fromJson( json, typeOfT );
            }
            else{
                return this.gson.fromJson( json, clazz );
            }
        }
        catch( JsonSyntaxException ex ){
            throw new HttpMessageNotReadableException( "Could not read JSON: " + ex.getMessage(), ex );
        }
        catch( JsonIOException ex ){
            throw new HttpMessageNotReadableException( "Could not read JSON: " + ex.getMessage(), ex );
        }
        catch( JsonParseException ex ){
            throw new HttpMessageNotReadableException( "Could not read JSON: " + ex.getMessage(), ex );
        }
    }

    @Override
    protected void writeInternal( Object o, HttpOutputMessage outputMessage )
            throws IOException, HttpMessageNotWritableException{

        OutputStreamWriter writer = new OutputStreamWriter( outputMessage.getBody(), getCharset( outputMessage.getHeaders() ) );

        try{
            if( this.prefixJson ){
                writer.append( "{} && " );
            }
            Type typeOfSrc = getType();
            if( typeOfSrc != null ){
                this.gson.toJson( o, typeOfSrc, writer );
            }
            else{
                this.gson.toJson( o, writer );
            }
            writer.close();
        }
        catch( JsonIOException ex ){
            throw new HttpMessageNotWritableException( "Could not write JSON: " + ex.getMessage(), ex );
        }
    }

    // helpers

    private Charset getCharset( HttpHeaders headers ){
        if( headers != null && headers.getContentType() != null
                && headers.getContentType().getCharSet() != null ){
            return headers.getContentType().getCharSet();
        }
        return DEFAULT_CHARSET;
    }

}