com.google.common.base.Joiner Maven / Gradle / Ivy
/*
* Copyright (C) 2008 Google 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 com.google.common.base;
import com.google.common.annotations.GwtCompatible;
import static com.google.common.base.Preconditions.checkNotNull;
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.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: {@code
*
* Joiner joiner = Joiner.on("; ").skipNulls();
* . . .
* return joiner.join("Harry", null, "Ron", "Hermione");}
*
* This returns the string {@code "Harry; Ron; Hermione"}. Note that all input
* elements are converted to strings using {@link Object#toString()} before
* being appended.
*
* If neither {@link #skipNulls()} nor {@link #useForNull(String)} is
* specified, the joining methods will throw {@link NullPointerException} if any
* given element is null.
*
*
Warning: joiner instances are always immutable; 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.
{@code
*
* // Bad! Do not do this!
* Joiner joiner = Joiner.on(',');
* joiner.skipNulls(); // does nothing!
* return joiner.join("wrong", null, "wrong");}
*
* @author Kevin Bourrillion
* @since 2 (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 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 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 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.
*/
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!
// TODO: fix that?
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.
*/
public Joiner skipNulls() {
return new Joiner(this) {
@Override public 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.
*/
public MapJoiner withKeyValueSeparator(String keyValueSeparator) {
return new MapJoiner(this, checkNotNull(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.
*/
public static class MapJoiner {
private final Joiner joiner;
private final String keyValueSeparator;
private MapJoiner(Joiner joiner, String keyValueSeparator) {
this.joiner = joiner;
this.keyValueSeparator = 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 appendTo(A appendable, Map map)
throws IOException {
checkNotNull(appendable);
Iterator> iterator = map.entrySet().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 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) {
try {
appendTo((Appendable) builder, map);
} catch (IOException impossible) {
throw new AssertionError(impossible);
}
return builder;
}
/**
* 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 appendTo(new StringBuilder(), map).toString();
}
/**
* Returns a map joiner with the same behavior as this one, except
* automatically substituting {@code nullText} for any provided null keys or
* values.
*/
public MapJoiner useForNull(String nullText) {
return new MapJoiner(joiner.useForNull(nullText), keyValueSeparator);
}
}
CharSequence toString(Object part) {
return (part instanceof CharSequence)
? (CharSequence) part
: part.toString();
}
private static Iterable