package com.github.jsonldjava.utils;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringReader;
import java.io.StringWriter;
import java.io.Writer;
import java.util.List;
import java.util.Map;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.github.jsonldjava.core.DocumentLoader;
import com.github.jsonldjava.core.JsonLdApi;
import com.github.jsonldjava.core.JsonLdProcessor;
/**
* Functions used to make loading, parsing, and serializing JSON easy using
* Jackson.
*
* @author tristan
*
*/
public class JsonUtils {
/**
* An HTTP Accept header that prefers JSONLD.
*/
protected static final String ACCEPT_HEADER = "application/ld+json, application/json;q=0.9, application/javascript;q=0.5, text/javascript;q=0.5, text/plain;q=0.2, */*;q=0.1";
private static final ObjectMapper JSON_MAPPER = new ObjectMapper();
private static final JsonFactory JSON_FACTORY = new JsonFactory(JSON_MAPPER);
private static DocumentLoader DOCUMENT_LOADER = new DocumentLoader();
static {
// Disable default Jackson behaviour to close
// InputStreams/Readers/OutputStreams/Writers
JSON_FACTORY.disable(JsonGenerator.Feature.AUTO_CLOSE_TARGET);
// Disable string retention features that may work for most JSON where
// the field names are in limited supply, but does not work for JSON-LD
// where a wide range of URIs are used for subjects and predicates
JSON_FACTORY.disable(JsonFactory.Feature.INTERN_FIELD_NAMES);
JSON_FACTORY.disable(JsonFactory.Feature.CANONICALIZE_FIELD_NAMES);
}
private JsonUtils() {
}
/**
* Parses a JSON-LD document from the given {@link InputStream} to an object
* that can be used as input for the {@link JsonLdApi} and
* {@link JsonLdProcessor} methods.<br>
* Uses UTF-8 as the character encoding when decoding the InputStream.
*
* @param input
* The JSON-LD document in an InputStream.
* @return A JSON Object.
* @throws JsonParseException
* If there was a JSON related error during parsing.
* @throws IOException
* If there was an IO error during parsing.
*/
public static Object fromInputStream(InputStream input) throws IOException {
// no readers from inputstreams w.o. encoding!!
return fromInputStream(input, "UTF-8");
}
/**
* Parses a JSON-LD document from the given {@link InputStream} to an object
* that can be used as input for the {@link JsonLdApi} and
* {@link JsonLdProcessor} methods.
*
* @param input
* The JSON-LD document in an InputStream.
* @param enc
* The character encoding to use when interpreting the characters
* in the InputStream.
* @return A JSON Object.
* @throws JsonParseException
* If there was a JSON related error during parsing.
* @throws IOException
* If there was an IO error during parsing.
*/
public static Object fromInputStream(InputStream input, String enc) throws IOException {
return fromReader(new BufferedReader(new InputStreamReader(input, enc)));
}
/**
* Parses a JSON-LD document from the given {@link Reader} to an object that
* can be used as input for the {@link JsonLdApi} and
* {@link JsonLdProcessor} methods.
*
* @param reader
* The JSON-LD document in a Reader.
* @return A JSON Object.
* @throws JsonParseException
* If there was a JSON related error during parsing.
* @throws IOException
* If there was an IO error during parsing.
*/
public static Object fromReader(Reader reader) throws IOException {
final JsonParser jp = JSON_FACTORY.createParser(reader);
Object rval ;
final JsonToken initialToken = jp.nextToken();
if (initialToken == JsonToken.START_ARRAY) {
rval = jp.readValueAs(List.class);
} else if (initialToken == JsonToken.START_OBJECT) {
rval = jp.readValueAs(Map.class);
} else if (initialToken == JsonToken.VALUE_STRING) {
rval = jp.readValueAs(String.class);
} else if (initialToken == JsonToken.VALUE_FALSE || initialToken == JsonToken.VALUE_TRUE) {
rval = jp.readValueAs(Boolean.class);
} else if (initialToken == JsonToken.VALUE_NUMBER_FLOAT
|| initialToken == JsonToken.VALUE_NUMBER_INT) {
rval = jp.readValueAs(Number.class);
} else if (initialToken == JsonToken.VALUE_NULL) {
rval = null;
} else {
throw new JsonParseException("document doesn't start with a valid json element : "
+ initialToken, jp.getCurrentLocation());
}
JsonToken t ;
try { t = jp.nextToken(); }
catch (JsonParseException ex) {
throw new JsonParseException("Document contains more content after json-ld element - (possible mismatched {}?)",
jp.getCurrentLocation());
}
if ( t != null )
throw new JsonParseException("Document contains possible json content after the json-ld element - (possible mismatched {}?)",
jp.getCurrentLocation());
return rval;
}
/**
* Parses a JSON-LD document from a string to an object that can be used as
* input for the {@link JsonLdApi} and {@link JsonLdProcessor} methods.
*
* @param jsonString
* The JSON-LD document as a string.
* @return A JSON Object.
* @throws JsonParseException
* If there was a JSON related error during parsing.
* @throws IOException
* If there was an IO error during parsing.
*/
public static Object fromString(String jsonString) throws JsonParseException, IOException {
return fromReader(new StringReader(jsonString));
}
/**
* Parses a JSON-LD document, from the contents of the JSON resource
* resolved from the JsonLdUrl, to an object that can be used as input for
* the {@link JsonLdApi} and {@link JsonLdProcessor} methods.
*
* @param url
* The JsonLdUrl to resolve
* @return A JSON Object.
* @throws JsonParseException
* If there was a JSON related error during parsing.
* @throws IOException
* If there was an IO error during parsing.
*/
public static Object fromURL(java.net.URL url) throws JsonParseException, IOException {
return DOCUMENT_LOADER.fromURL(url);
}
/**
* Writes the given JSON-LD Object out to a String, using indentation and
* new lines to improve readability.
*
* @param jsonObject
* The JSON-LD Object to serialize.
* @return A JSON document serialised to a String.
* @throws JsonGenerationException
* If there is a JSON error during serialization.
* @throws IOException
* If there is an IO error during serialization.
*/
public static String toPrettyString(Object jsonObject) throws JsonGenerationException,
IOException {
final StringWriter sw = new StringWriter();
writePrettyPrint(sw, jsonObject);
return sw.toString();
}
/**
* Writes the given JSON-LD Object out to a String.
*
* @param jsonObject
* The JSON-LD Object to serialize.
* @return A JSON document serialised to a String.
* @throws JsonGenerationException
* If there is a JSON error during serialization.
* @throws IOException
* If there is an IO error during serialization.
*/
public static String toString(Object jsonObject) throws JsonGenerationException, IOException {
final StringWriter sw = new StringWriter();
write(sw, jsonObject);
return sw.toString();
}
/**
* Writes the given JSON-LD Object out to the given Writer.
*
* @param writer
* The writer that is to receive the serialized JSON-LD object.
* @param jsonObject
* The JSON-LD Object to serialize.
* @throws JsonGenerationException
* If there is a JSON error during serialization.
* @throws IOException
* If there is an IO error during serialization.
*/
public static void write(Writer writer, Object jsonObject) throws JsonGenerationException,
IOException {
final JsonGenerator jw = JSON_FACTORY.createGenerator(writer);
jw.writeObject(jsonObject);
}
/**
* Writes the given JSON-LD Object out to the given Writer, using
* indentation and new lines to improve readability.
*
* @param writer
* The writer that is to receive the serialized JSON-LD object.
* @param jsonObject
* The JSON-LD Object to serialize.
* @throws JsonGenerationException
* If there is a JSON error during serialization.
* @throws IOException
* If there is an IO error during serialization.
*/
public static void writePrettyPrint(Writer writer, Object jsonObject)
throws JsonGenerationException, IOException {
final JsonGenerator jw = JSON_FACTORY.createGenerator(writer);
jw.useDefaultPrettyPrinter();
jw.writeObject(jsonObject);
}
}