org.apache.hadoop.util.JsonSerialization Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.hadoop.util;
import java.io.EOFException;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Map;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectReader;
import com.fasterxml.jackson.databind.ObjectWriter;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.google.common.base.Preconditions;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
/**
* Support for marshalling objects to and from JSON.
*
* It constructs an object mapper as an instance field.
* and synchronizes access to those methods
* which use the mapper.
*
* This class was extracted from
* {@code org.apache.hadoop.registry.client.binding.JsonSerDeser},
* which is now a subclass of this class.
* @param Type to marshal.
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class JsonSerialization {
private static final Logger LOG =
LoggerFactory.getLogger(JsonSerialization.class);
private static final String UTF_8 = "UTF-8";
private final Class classType;
private final ObjectMapper mapper;
private static final ObjectWriter WRITER =
new ObjectMapper().writerWithDefaultPrettyPrinter();
private static final ObjectReader MAP_READER =
new ObjectMapper().readerFor(Map.class);
/**
* @return an ObjectWriter which pretty-prints its output
*/
public static ObjectWriter writer() {
return WRITER;
}
/**
* @return an ObjectReader which returns simple Maps.
*/
public static ObjectReader mapReader() {
return MAP_READER;
}
/**
* Create an instance bound to a specific type.
* @param classType class to marshall
* @param failOnUnknownProperties fail if an unknown property is encountered.
* @param pretty generate pretty (indented) output?
*/
public JsonSerialization(Class classType,
boolean failOnUnknownProperties, boolean pretty) {
Preconditions.checkArgument(classType != null, "null classType");
this.classType = classType;
this.mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,
failOnUnknownProperties);
mapper.configure(SerializationFeature.INDENT_OUTPUT, pretty);
}
/**
* Get the simple name of the class type to be marshalled.
* @return the name of the class being marshalled
*/
public String getName() {
return classType.getSimpleName();
}
/**
* Get the mapper of this class.
* @return the mapper
*/
public ObjectMapper getMapper() {
return mapper;
}
/**
* Convert from JSON.
*
* @param json input
* @return the parsed JSON
* @throws IOException IO problems
* @throws JsonParseException If the input is not well-formatted
* @throws JsonMappingException failure to map from the JSON to this class
*/
@SuppressWarnings("unchecked")
public synchronized T fromJson(String json)
throws IOException, JsonParseException, JsonMappingException {
if (json.isEmpty()) {
throw new EOFException("No data");
}
try {
return mapper.readValue(json, classType);
} catch (IOException e) {
LOG.error("Exception while parsing json : {}\n{}", e, json, e);
throw e;
}
}
/**
* Read from an input stream.
* @param stream stream to read from
* @return the parsed entity
* @throws IOException IO problems
* @throws JsonParseException If the input is not well-formatted
* @throws JsonMappingException failure to map from the JSON to this class
*/
public synchronized T fromJsonStream(InputStream stream) throws IOException {
return mapper.readValue(stream, classType);
}
/**
* Load from a JSON text file.
* @param jsonFile input file
* @return the parsed JSON
* @throws IOException IO problems
* @throws JsonParseException If the input is not well-formatted
* @throws JsonMappingException failure to map from the JSON to this class
*/
@SuppressWarnings("unchecked")
public synchronized T load(File jsonFile)
throws IOException, JsonParseException, JsonMappingException {
if (!jsonFile.isFile()) {
throw new FileNotFoundException("Not a file: " + jsonFile);
}
if (jsonFile.length() == 0) {
throw new EOFException("File is empty: " + jsonFile);
}
try {
return mapper.readValue(jsonFile, classType);
} catch (IOException e) {
LOG.error("Exception while parsing json file {}", jsonFile, e);
throw e;
}
}
/**
* Save to a local file. Any existing file is overwritten unless
* the OS blocks that.
* @param file file
* @param path path
* @throws IOException IO exception
*/
public void save(File file, T instance) throws
IOException {
writeJsonAsBytes(instance, new FileOutputStream(file));
}
/**
* Convert from a JSON file.
* @param resource input file
* @return the parsed JSON
* @throws IOException IO problems
* @throws JsonParseException If the input is not well-formatted
* @throws JsonMappingException failure to map from the JSON to this class
*/
@SuppressWarnings({"IOResourceOpenedButNotSafelyClosed"})
public synchronized T fromResource(String resource)
throws IOException, JsonParseException, JsonMappingException {
try (InputStream resStream = this.getClass()
.getResourceAsStream(resource)) {
if (resStream == null) {
throw new FileNotFoundException(resource);
}
return mapper.readValue(resStream, classType);
} catch (IOException e) {
LOG.error("Exception while parsing json resource {}", resource, e);
throw e;
}
}
/**
* clone by converting to JSON and back again.
* This is much less efficient than any Java clone process.
* @param instance instance to duplicate
* @return a new instance
* @throws IOException IO problems.
*/
public T fromInstance(T instance) throws IOException {
return fromJson(toJson(instance));
}
/**
* Load from a Hadoop filesystem.
* There's a check for data availability after the file is open, by
* raising an EOFException if stream.available == 0.
* This allows for a meaningful exception without the round trip overhead
* of a getFileStatus call before opening the file. It may be brittle
* against an FS stream which doesn't return a value here, but the
* standard filesystems all do.
* JSON parsing and mapping problems
* are converted to IOEs.
* @param fs filesystem
* @param path path
* @return a loaded object
* @throws IOException IO or JSON parse problems
*/
public T load(FileSystem fs, Path path) throws IOException {
try (FSDataInputStream dataInputStream = fs.open(path)) {
// throw an EOF exception if there is no data available.
if (dataInputStream.available() == 0) {
throw new EOFException("No data in " + path);
}
return fromJsonStream(dataInputStream);
} catch (JsonProcessingException e) {
throw new IOException(
String.format("Failed to read JSON file \"%s\": %s", path, e),
e);
}
}
/**
* Save to a Hadoop filesystem.
* @param fs filesystem
* @param path path
* @param overwrite should any existing file be overwritten
* @throws IOException IO exception
*/
public void save(FileSystem fs, Path path, T instance,
boolean overwrite) throws
IOException {
writeJsonAsBytes(instance, fs.create(path, overwrite));
}
/**
* Write the JSON as bytes, then close the file.
* @param dataOutputStream an output stream that will always be closed
* @throws IOException on any failure
*/
private void writeJsonAsBytes(T instance,
OutputStream dataOutputStream) throws IOException {
try {
dataOutputStream.write(toBytes(instance));
} finally {
dataOutputStream.close();
}
}
/**
* Convert JSON to bytes.
* @param instance instance to convert
* @return a byte array
* @throws IOException IO problems
*/
public byte[] toBytes(T instance) throws IOException {
return mapper.writeValueAsBytes(instance);
}
/**
* Deserialize from a byte array.
* @param bytes byte array
* @throws IOException IO problems
* @throws EOFException not enough data
*/
public T fromBytes(byte[] bytes) throws IOException {
return fromJson(new String(bytes, 0, bytes.length, UTF_8));
}
/**
* Convert an instance to a JSON string.
* @param instance instance to convert
* @return a JSON string description
* @throws JsonProcessingException Json generation problems
*/
public synchronized String toJson(T instance) throws JsonProcessingException {
return mapper.writeValueAsString(instance);
}
/**
* Convert an instance to a string form for output. This is a robust
* operation which will convert any JSON-generating exceptions into
* error text.
* @param instance non-null instance
* @return a JSON string
*/
public String toString(T instance) {
Preconditions.checkArgument(instance != null, "Null instance argument");
try {
return toJson(instance);
} catch (JsonProcessingException e) {
return "Failed to convert to a string: " + e;
}
}
}
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