/*
* Copyright (C) 2008 The Guava Authors
*
* 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 com.google.common.base;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import java.io.IOException;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;
/**
* An object which joins pieces of text (specified as an array, {@link Iterable}, varargs or even a
* {@link Map}) with a separator. It either appends the results to an {@link Appendable} or returns
* them as a {@link String}. Example: <pre> {@code
*
* Joiner joiner = Joiner.on("; ").skipNulls();
* . . .
* return joiner.join("Harry", null, "Ron", "Hermione");}</pre>
*
* This returns the string {@code "Harry; Ron; Hermione"}. Note that all input elements are
* converted to strings using {@link Object#toString()} before being appended.
*
* <p>If neither {@link #skipNulls()} nor {@link #useForNull(String)} is specified, the joining
* methods will throw {@link NullPointerException} if any given element is null.
*
* <p><b>Warning: joiner instances are always immutable</b>; a configuration method such as {@code
* useForNull} has no effect on the instance it is invoked on! You must store and use the new joiner
* instance returned by the method. This makes joiners thread-safe, and safe to store as {@code
* static final} constants. <pre> {@code
*
* // Bad! Do not do this!
* Joiner joiner = Joiner.on(',');
* joiner.skipNulls(); // does nothing!
* return joiner.join("wrong", null, "wrong");}</pre>
*
* @author Kevin Bourrillion
* @since 2.0 (imported from Google Collections Library)
*/
@GwtCompatible
public class Joiner {
/**
* Returns a joiner which automatically places {@code separator} between consecutive elements.
*/
public static Joiner on(String separator) {
return new Joiner(separator);
}
/**
* Returns a joiner which automatically places {@code separator} between consecutive elements.
*/
public static Joiner on(char separator) {
return new Joiner(String.valueOf(separator));
}
private final String separator;
private Joiner(String separator) {
this.separator = checkNotNull(separator);
}
private Joiner(Joiner prototype) {
this.separator = prototype.separator;
}
/**
* Appends the string representation of each of {@code parts}, using the previously configured
* separator between each, to {@code appendable}.
*/
public <A extends Appendable> A appendTo(A appendable, Iterable<?> parts) throws IOException {
checkNotNull(appendable);
Iterator<?> iterator = parts.iterator();
if (iterator.hasNext()) {
appendable.append(toString(iterator.next()));
while (iterator.hasNext()) {
appendable.append(separator);
appendable.append(toString(iterator.next()));
}
}
return appendable;
}
/**
* Appends the string representation of each of {@code parts}, using the previously configured
* separator between each, to {@code appendable}.
*/
public final <A extends Appendable> A appendTo(A appendable, Object[] parts) throws IOException {
return appendTo(appendable, Arrays.asList(parts));
}
/**
* Appends to {@code appendable} the string representation of each of the remaining arguments.
*/
public final <A extends Appendable> A appendTo(
A appendable, @Nullable Object first, @Nullable Object second, Object... rest)
throws IOException {
return appendTo(appendable, iterable(first, second, rest));
}
/**
* Appends the string representation of each of {@code parts}, using the previously configured
* separator between each, to {@code builder}. Identical to {@link #appendTo(Appendable,
* Iterable)}, except that it does not throw {@link IOException}.
*/
public final StringBuilder appendTo(StringBuilder builder, Iterable<?> parts) {
try {
appendTo((Appendable) builder, parts);
} catch (IOException impossible) {
throw new AssertionError(impossible);
}
return builder;
}
/**
* Appends the string representation of each of {@code parts}, using the previously configured
* separator between each, to {@code builder}. Identical to {@link #appendTo(Appendable,
* Iterable)}, except that it does not throw {@link IOException}.
*/
public final StringBuilder appendTo(StringBuilder builder, Object[] parts) {
return appendTo(builder, Arrays.asList(parts));
}
/**
* Appends to {@code builder} the string representation of each of the remaining arguments.
* Identical to {@link #appendTo(Appendable, Object, Object, Object...)}, except that it does not
* throw {@link IOException}.
*/
public final StringBuilder appendTo(
StringBuilder builder, @Nullable Object first, @Nullable Object second, Object... rest) {
return appendTo(builder, iterable(first, second, rest));
}
/**
* Returns a string containing the string representation of each of {@code parts}, using the
* previously configured separator between each.
*/
public final String join(Iterable<?> parts) {
return appendTo(new StringBuilder(), parts).toString();
}
/**
* Returns a string containing the string representation of each of {@code parts}, using the
* previously configured separator between each.
*/
public final String join(Object[] parts) {
return join(Arrays.asList(parts));
}
/**
* Returns a string containing the string representation of each argument, using the previously
* configured separator between each.
*/
public final String join(@Nullable Object first, @Nullable Object second, Object... rest) {
return join(iterable(first, second, rest));
}
/**
* Returns a joiner with the same behavior as this one, except automatically substituting {@code
* nullText} for any provided null elements.
*/
@CheckReturnValue
public Joiner useForNull(final String nullText) {
checkNotNull(nullText);
return new Joiner(this) {
@Override CharSequence toString(Object part) {
return (part == null) ? nullText : Joiner.this.toString(part);
}
@Override public Joiner useForNull(String nullText) {
checkNotNull(nullText); // weird: just to satisfy NullPointerTester.
throw new UnsupportedOperationException("already specified useForNull");
}
@Override public Joiner skipNulls() {
throw new UnsupportedOperationException("already specified useForNull");
}
};
}
/**
* Returns a joiner with the same behavior as this joiner, except automatically skipping over any
* provided null elements.
*/
@CheckReturnValue
public Joiner skipNulls() {
return new Joiner(this) {
@Override public <A extends Appendable> A appendTo(A appendable, Iterable<?> parts)
throws IOException {
checkNotNull(appendable, "appendable");
checkNotNull(parts, "parts");
Iterator<?> iterator = parts.iterator();
while (iterator.hasNext()) {
Object part = iterator.next();
if (part != null) {
appendable.append(Joiner.this.toString(part));
break;
}
}
while (iterator.hasNext()) {
Object part = iterator.next();
if (part != null) {
appendable.append(separator);
appendable.append(Joiner.this.toString(part));
}
}
return appendable;
}
@Override public Joiner useForNull(String nullText) {
checkNotNull(nullText); // weird: just to satisfy NullPointerTester.
throw new UnsupportedOperationException("already specified skipNulls");
}
@Override public MapJoiner withKeyValueSeparator(String kvs) {
checkNotNull(kvs); // weird: just to satisfy NullPointerTester.
throw new UnsupportedOperationException("can't use .skipNulls() with maps");
}
};
}
/**
* Returns a {@code MapJoiner} using the given key-value separator, and the same configuration as
* this {@code Joiner} otherwise.
*/
@CheckReturnValue
public MapJoiner withKeyValueSeparator(String keyValueSeparator) {
return new MapJoiner(this, keyValueSeparator);
}
/**
* An object that joins map entries in the same manner as {@code Joiner} joins iterables and
* arrays. Like {@code Joiner}, it is thread-safe and immutable.
*
* <p>In addition to operating on {@code Map} instances, {@code MapJoiner} can operate on {@code
* Multimap} entries in two distinct modes:
*
* <ul>
* <li>To output a separate entry for each key-value pair, pass {@code multimap.entries()} to a
* {@code MapJoiner} method that accepts entries as input, and receive output of the form
* {@code key1=A&key1=B&key2=C}.
* <li>To output a single entry for each key, pass {@code multimap.asMap()} to a {@code MapJoiner}
* method that accepts a map as input, and receive output of the form {@code
* key1=[A, B]&key2=C}.
* </ul>
*
* @since 2.0 (imported from Google Collections Library)
*/
public final static class MapJoiner {
private final Joiner joiner;
private final String keyValueSeparator;
private MapJoiner(Joiner joiner, String keyValueSeparator) {
this.joiner = joiner; // only "this" is ever passed, so don't checkNotNull
this.keyValueSeparator = checkNotNull(keyValueSeparator);
}
/**
* Appends the string representation of each entry of {@code map}, using the previously
* configured separator and key-value separator, to {@code appendable}.
*/
public <A extends Appendable> A appendTo(A appendable, Map<?, ?> map) throws IOException {
return appendTo(appendable, map.entrySet());
}
/**
* Appends the string representation of each entry of {@code map}, using the previously
* configured separator and key-value separator, to {@code builder}. Identical to {@link
* #appendTo(Appendable, Map)}, except that it does not throw {@link IOException}.
*/
public StringBuilder appendTo(StringBuilder builder, Map<?, ?> map) {
return appendTo(builder, map.entrySet());
}
/**
* Returns a string containing the string representation of each entry of {@code map}, using the
* previously configured separator and key-value separator.
*/
public String join(Map<?, ?> map) {
return join(map.entrySet());
}
/**
* Appends the string representation of each entry in {@code entries}, using the previously
* configured separator and key-value separator, to {@code appendable}.
*
* @since 10.0
*/
@Beta
public <A extends Appendable> A appendTo(A appendable, Iterable<? extends Entry<?, ?>> entries)
throws IOException {
checkNotNull(appendable);
Iterator<? extends Map.Entry<?, ?>> iterator = entries.iterator();
if (iterator.hasNext()) {
Entry<?, ?> entry = iterator.next();
appendable.append(joiner.toString(entry.getKey()));
appendable.append(keyValueSeparator);
appendable.append(joiner.toString(entry.getValue()));
while (iterator.hasNext()) {
appendable.append(joiner.separator);
Entry<?, ?> e = iterator.next();
appendable.append(joiner.toString(e.getKey()));
appendable.append(keyValueSeparator);
appendable.append(joiner.toString(e.getValue()));
}
}
return appendable;
}
/**
* Appends the string representation of each entry in {@code entries}, using the previously
* configured separator and key-value separator, to {@code builder}. Identical to {@link
* #appendTo(Appendable, Iterable)}, except that it does not throw {@link IOException}.
*
* @since 10.0
*/
@Beta
public StringBuilder appendTo(StringBuilder builder, Iterable<? extends Entry<?, ?>> entries) {
try {
appendTo((Appendable) builder, entries);
} catch (IOException impossible) {
throw new AssertionError(impossible);
}
return builder;
}
/**
* Returns a string containing the string representation of each entry in {@code entries}, using
* the previously configured separator and key-value separator.
*
* @since 10.0
*/
@Beta
public String join(Iterable<? extends Entry<?, ?>> entries) {
return appendTo(new StringBuilder(), entries).toString();
}
/**
* Returns a map joiner with the same behavior as this one, except automatically substituting
* {@code nullText} for any provided null keys or values.
*/
@CheckReturnValue
public MapJoiner useForNull(String nullText) {
return new MapJoiner(joiner.useForNull(nullText), keyValueSeparator);
}
}
CharSequence toString(Object part) {
checkNotNull(part); // checkNotNull for GWT (do not optimize).
return (part instanceof CharSequence) ? (CharSequence) part : part.toString();
}
private static Iterable<Object> iterable(
final Object first, final Object second, final Object[] rest) {
checkNotNull(rest);
return new AbstractList<Object>() {
@Override public int size() {
return rest.length + 2;
}
@Override public Object get(int index) {
switch (index) {
case 0:
return first;
case 1:
return second;
default:
return rest[index - 2];
}
}
};
}
}
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