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Decoders.java
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157 lines (145 loc) · 5.46 KB
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/*
* Copyright 2013 Netflix, Inc.
*
* 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 feign.codec;
import java.io.Reader;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import static feign.Util.checkNotNull;
import static java.lang.String.format;
import static java.util.regex.Pattern.DOTALL;
import static java.util.regex.Pattern.compile;
/**
* Static utility methods pertaining to {@code Decoder} instances.
* <br>
* <br><br><b>Pattern Decoders</b><br>
* <br>
* Pattern decoders typically require less initialization, dependencies, and
* code than reflective decoders, but not can be awkward to those unfamiliar
* with regex. Typical use of pattern decoders is to grab a single field from an
* xml response, or parse a list of Strings. The pattern decoders here
* facilitate these use cases.
*/
public class Decoders {
/**
* guava users will implement this with {@code ApplyFirstGroup<String, T>}.
*
* @param <T> intended result type
*/
public interface ApplyFirstGroup<T> {
/**
* create a new instance from the non-null {@code firstGroup} specified.
*/
T apply(String firstGroup);
}
/**
* The first match group is applied to {@code applyGroups} and result
* returned. If no matches are found, the response is null;
* <br>
* Ex. to pull the first interesting element from an xml response:
* <br>
* <pre>
* decodeFirstDirPoolID = transformFirstGroup("<DirPoolID[ˆ>]*>([ˆ<]+)</DirPoolID>", ToLong.INSTANCE);
* </pre>
*/
public static <T> Decoder transformFirstGroup(String pattern, final ApplyFirstGroup<T> applyFirstGroup) {
final Pattern patternForMatcher = compile(checkNotNull(pattern, "pattern"), DOTALL);
checkNotNull(applyFirstGroup, "applyFirstGroup");
return new Decoder() {
@Override
public Object decode(String methodKey, Reader reader, Type type) throws Throwable {
Matcher matcher = patternForMatcher.matcher(Decoders.toString(reader));
if (matcher.find()) {
return applyFirstGroup.apply(matcher.group(1));
}
return null;
}
@Override public String toString() {
return format("decode groups from %s into %s", patternForMatcher, applyFirstGroup);
}
};
}
/**
* shortcut for {@link Decoders#transformFirstGroup(String, ApplyFirstGroup)} when
* {@code String} is the type you are decoding into.
* <br>
* <br>
* Ex. to pull the first interesting element from an xml response:
* <br>
* <pre>
* decodeFirstDirPoolID = firstGroup("<DirPoolID[ˆ>]*>([ˆ<]+)</DirPoolID>");
* </pre>
*/
public static Decoder firstGroup(String pattern) {
return transformFirstGroup(pattern, IDENTITY);
}
/**
* On the each find the first match group is applied to
* {@code applyFirstGroup} and added to the list returned. If no matches are
* found, the response is an empty list;
* <br>
* Ex. to pull a list zones constructed from http paths starting with
* {@code /Rest/Zone/}:
* <br>
* <pre>
* decodeListOfZones = transformEachFirstGroup("/REST/Zone/([ˆ/]+)/", ToZone.INSTANCE);
* </pre>
*/
public static <T> Decoder transformEachFirstGroup(String pattern, final ApplyFirstGroup<T> applyFirstGroup) {
final Pattern patternForMatcher = compile(checkNotNull(pattern, "pattern"), DOTALL);
checkNotNull(applyFirstGroup, "applyFirstGroup");
return new Decoder() {
@Override
public List<T> decode(String methodKey, Reader reader, Type type) throws Throwable {
Matcher matcher = patternForMatcher.matcher(Decoders.toString(reader));
List<T> result = new ArrayList<T>();
while (matcher.find()) {
result.add(applyFirstGroup.apply(matcher.group(1)));
}
return result;
}
@Override public String toString() {
return format("decode %s into list elements, where each group(1) is transformed with %s",
patternForMatcher, applyFirstGroup);
}
};
}
/**
* shortcut for {@link Decoders#transformEachFirstGroup(String, ApplyFirstGroup)}
* when {@code List<String>} is the type you are decoding into.
* <br>
* Ex. to pull a list zones names, which are http paths starting with
* {@code /Rest/Zone/}:
* <br>
* <pre>
* decodeListOfZonesNames = eachFirstGroup("/REST/Zone/([ˆ/]+)/");
* </pre>
*/
public static Decoder eachFirstGroup(String pattern) {
return transformEachFirstGroup(pattern, IDENTITY);
}
private static String toString(Reader reader) throws Throwable {
return TO_STRING.decode(null, reader, null).toString();
}
private static final Decoder TO_STRING = new ToStringDecoder();
private static final ApplyFirstGroup<String> IDENTITY = new ApplyFirstGroup<String>() {
@Override public String apply(String firstGroup) {
return firstGroup;
}
};
}