package com.github.aaronshan.functions.utils.json;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.core.io.SerializedString;
import com.google.common.base.Throwables;
import com.google.common.collect.ImmutableList;
import java.io.IOException;
import java.io.StringWriter;
import static com.fasterxml.jackson.core.JsonFactory.Feature.CANONICALIZE_FIELD_NAMES;
import static com.fasterxml.jackson.core.JsonToken.*;
/**
* @author ruifeng.shan
* date: 2016-07-25
* time: 15:02
*/
public class JsonExtract {
private static final JsonFactory JSON_FACTORY = new JsonFactory()
.disable(CANONICALIZE_FIELD_NAMES);
private JsonExtract() {
}
public static <T> T extract(String jsonInput, JsonExtractor<T> jsonExtractor) {
if (jsonInput == null) {
throw new NullPointerException("jsonInput is null");
}
try {
JsonParser jsonParser = JSON_FACTORY.createParser(jsonInput);
// Initialize by advancing to first token and make sure it exists
if (jsonParser.nextToken() == null) {
return null;
}
return jsonExtractor.extract(jsonParser);
} catch (JsonParseException e) {
// Return null if we failed to parse something
return null;
} catch (IOException e) {
throw Throwables.propagate(e);
}
}
public static <T> JsonExtractor<T> generateExtractor(String path, JsonExtractor<T> rootExtractor) {
return generateExtractor(path, rootExtractor, false);
}
public static <T> JsonExtractor<T> generateExtractor(String path, JsonExtractor<T> rootExtractor, boolean exceptionOnOutOfBounds) {
ImmutableList<String> tokens = ImmutableList.copyOf(new JsonPathTokenizer(path));
JsonExtractor<T> jsonExtractor = rootExtractor;
for (String token : tokens.reverse()) {
jsonExtractor = new ObjectFieldJsonExtractor(token, jsonExtractor, exceptionOnOutOfBounds);
}
return jsonExtractor;
}
private static int tryParseInt(String fieldName, int defaultValue) {
int index = defaultValue;
try {
index = Integer.parseInt(fieldName);
} catch (NumberFormatException ignored) {
}
return index;
}
public interface JsonExtractor<T> {
/**
* Executes the extraction on the existing content of the JsonParser and outputs the match.
* Notes:
* <ul>
* <li>JsonParser must be on the FIRST token of the value to be processed when extract is called</li>
* <li>INVARIANT: when extract() returns, the current token of the parser will be the LAST token of the value</li>
* </ul>
*
* @param jsonParser json parser
* @return the value, or null if not applicable
* @throws IOException IO exception
*/
T extract(JsonParser jsonParser)
throws IOException;
}
public static class ObjectFieldJsonExtractor<T>
implements JsonExtractor<T> {
private final SerializedString fieldName;
private final JsonExtractor<? extends T> delegate;
private final int index;
private final boolean exceptionOnOutOfBounds;
public ObjectFieldJsonExtractor(String fieldName, JsonExtractor<? extends T> delegate) {
this(fieldName, delegate, false);
}
public ObjectFieldJsonExtractor(String fieldName, JsonExtractor<? extends T> delegate, boolean exceptionOnOutOfBounds) {
if (fieldName == null) {
throw new NullPointerException("jsonInput is null");
}
if (delegate == null) {
throw new NullPointerException("delegate is null");
}
this.fieldName = new SerializedString(fieldName);
this.delegate = delegate;
this.exceptionOnOutOfBounds = exceptionOnOutOfBounds;
this.index = tryParseInt(fieldName, -1);
}
public T extract(JsonParser jsonParser)
throws IOException {
if (jsonParser.getCurrentToken() == START_OBJECT) {
return processJsonObject(jsonParser);
}
if (jsonParser.getCurrentToken() == START_ARRAY) {
return processJsonArray(jsonParser);
}
throw new JsonParseException("Expected a JSON object or array", jsonParser.getCurrentLocation());
}
public T processJsonObject(JsonParser jsonParser)
throws IOException {
while (!jsonParser.nextFieldName(fieldName)) {
if (!jsonParser.hasCurrentToken()) {
throw new JsonParseException("Unexpected end of object", jsonParser.getCurrentLocation());
}
if (jsonParser.getCurrentToken() == END_OBJECT) {
// Unable to find matching field
return null;
}
jsonParser.skipChildren(); // Skip nested structure if currently at the start of one
}
jsonParser.nextToken(); // Shift to first token of the value
return delegate.extract(jsonParser);
}
public T processJsonArray(JsonParser jsonParser) throws IOException {
int currentIndex = 0;
while (true) {
JsonToken token = jsonParser.nextToken();
if (token == null) {
throw new JsonParseException("Unexpected end of array", jsonParser.getCurrentLocation());
}
if (token == END_ARRAY) {
// Index out of bounds
if (exceptionOnOutOfBounds) {
throw new RuntimeException("Index out of bounds");
}
return null;
}
if (currentIndex == index) {
break;
}
currentIndex++;
jsonParser.skipChildren(); // Skip nested structure if currently at the start of one
}
return delegate.extract(jsonParser);
}
}
public static class ScalarValueJsonExtractor
implements JsonExtractor<String> {
public String extract(JsonParser jsonParser)
throws IOException {
JsonToken token = jsonParser.getCurrentToken();
if (token == null) {
throw new JsonParseException("Unexpected end of value", jsonParser.getCurrentLocation());
}
if (!token.isScalarValue() || token == VALUE_NULL) {
return null;
}
return jsonParser.getText();
}
}
public static class JsonValueJsonExtractor
implements JsonExtractor<String> {
public String extract(JsonParser jsonParser)
throws IOException {
if (!jsonParser.hasCurrentToken()) {
throw new JsonParseException("Unexpected end of value", jsonParser.getCurrentLocation());
}
StringWriter stringWriter = new StringWriter();
try {
JsonGenerator jsonGenerator = JSON_FACTORY.createGenerator(stringWriter);
jsonGenerator.copyCurrentStructure(jsonParser);
jsonGenerator.flush();
jsonGenerator.close();
} catch (IOException e) {
return null;
}
return stringWriter.toString();
}
}
public static class JsonSizeExtractor
implements JsonExtractor<Long> {
public Long extract(JsonParser jsonParser)
throws IOException {
if (!jsonParser.hasCurrentToken()) {
throw new JsonParseException("Unexpected end of value", jsonParser.getCurrentLocation());
}
if (jsonParser.getCurrentToken() == START_ARRAY) {
long length = 0;
while (true) {
JsonToken token = jsonParser.nextToken();
if (token == null) {
return null;
}
if (token == END_ARRAY) {
return length;
}
jsonParser.skipChildren();
length++;
}
}
if (jsonParser.getCurrentToken() == START_OBJECT) {
long length = 0;
while (true) {
JsonToken token = jsonParser.nextToken();
if (token == null) {
return null;
}
if (token == END_OBJECT) {
return length;
}
if (token == FIELD_NAME) {
length++;
} else {
jsonParser.skipChildren();
}
}
}
return 0L;
}
}
}
