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Json-LD core implementation
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 org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.client.protocol.RequestAcceptEncoding;
import org.apache.http.client.protocol.ResponseContentEncoding;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.cache.BasicHttpCacheStorage;
import org.apache.http.impl.client.cache.CacheConfig;
import org.apache.http.impl.client.cache.CachingHttpClientBuilder;
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.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.
*/
public 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 volatile CloseableHttpClient DEFAULT_HTTP_CLIENT;
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);
}
/**
* 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.
* 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.
* @deprecated Use {@link #fromURL(java.net.URL, CloseableHttpClient)} instead.
*/
@Deprecated
public static Object fromURL(java.net.URL url) throws JsonParseException, IOException {
return fromURL(url, getDefaultHttpClient());
}
/**
* 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);
}
/**
* Attempts to open an {@link InputStream} that will contain the content of the URL, as resolved by the given HTTP Client.
*
* If the URL is not an HTTP or HTTPS URL it is resolved using the default {@link java.net.URL#openStream()} method.
* @param url The URL to resolve.
* @param httpClient The CloseableHttpClient to use to resolve the URL.
* @return An InputStream containing the contents of the resolved URL.
* @throws IOException If there are any IO exceptions while resolving the URL.
*/
public static InputStream openStreamForURL(java.net.URL url, CloseableHttpClient httpClient) throws IOException {
final String protocol = url.getProtocol();
if (!protocol.equalsIgnoreCase("http") && !protocol.equalsIgnoreCase("https")) {
// Can't use the HTTP client for those!
// Fallback to Java's built-in JsonLdUrl handler. No need for
// Accept headers as it's likely to be file: or jar:
return url.openStream();
}
final HttpUriRequest request = new HttpGet(url.toExternalForm());
// We prefer application/ld+json, but fallback to application/json
// or whatever is available
request.addHeader("Accept", ACCEPT_HEADER);
final CloseableHttpResponse response = httpClient.execute(request);
try {
final int status = response.getStatusLine().getStatusCode();
if (status != 200 && status != 203) {
throw new IOException("Can't retrieve " + url + ", status code: " + status);
}
return response.getEntity().getContent();
} finally {
if (response != null) {
response.close();
}
}
}
/**
* 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
* @param httpClient
* The {@link CloseableHttpClient} to use to resolve the URL.
* @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, CloseableHttpClient httpClient) throws JsonParseException, IOException {
final InputStream in = openStreamForURL(url, httpClient);
try {
return fromInputStream(in);
} finally {
in.close();
}
}
public static CloseableHttpClient getDefaultHttpClient() {
CloseableHttpClient result = DEFAULT_HTTP_CLIENT;
if (result == null) {
synchronized (JsonUtils.class) {
result = DEFAULT_HTTP_CLIENT;
if (result == null) {
result = DEFAULT_HTTP_CLIENT = JsonUtils.createDefaultHttpClient();
}
}
}
return result;
}
private static CloseableHttpClient createDefaultHttpClient() {
// Common CacheConfig for both the JarCacheStorage and the underlying
// BasicHttpCacheStorage
final CacheConfig cacheConfig = CacheConfig.custom().setMaxCacheEntries(1000)
.setMaxObjectSize(1024 * 128).build();
CloseableHttpClient result = CachingHttpClientBuilder
.create()
// allow caching
.setCacheConfig(cacheConfig)
// Wrap the local JarCacheStorage around a BasicHttpCacheStorage
.setHttpCacheStorage(
new JarCacheStorage(null, cacheConfig, new BasicHttpCacheStorage(
cacheConfig)))
// Support compressed data
// http://hc.apache.org/httpcomponents-client-ga/tutorial/html/httpagent.html#d5e1238
.addInterceptorFirst(new RequestAcceptEncoding())
.addInterceptorFirst(new ResponseContentEncoding())
// use system defaults for proxy etc.
.useSystemProperties().build();
return result;
}
}
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