Guava-String-Joiner
目录
1. Joiner 用法
- 连接字符串
Joiner joiner = Joiner.on("; ").skipNulls();
joiner.join("Harry", null, "Ron", "Hermione");
- 使用在对象上
Joiner.on(",").join(Arrays.asList(1, 5, 7)); // returns "1,5,7"
joiner实例通常是不可变的，Joiner线程安全，使用静态常量方式：static final
2. Joiner属性
- 分隔符保存为
separator
private final String separator;
3. Appendable接口(jdk)
-
提供了append方法
Appendable append(CharSequence csq) throws IOException;
Appendable append(CharSequence csq, int start, int end) throws IOException;
Appendable append(char c) throws IOException; -
哪些实现了
CharSequence？
String
StringBuiler
3. Joiner方法
1. on
2. appendTo
3. join
4. useForNull
5. skipNulls
6. withKeyValueSeparator
7. toString
8. iterable（私有）
3.1 on
- 构造函数私有不能调用
private Joiner(String separator) {
this.separator = (String)Preconditions.checkNotNull(separator);
}
- on是静态工厂
- 构造一个
Joiner - 设置分隔符
separator
- 构造一个
public static Joiner on(String separator) {
return new Joiner(separator);
}
public static Joiner on(char separator) {
return new Joiner(String.valueOf(separator));
}
toSring
- toString是Joiner内置的方法(获取CharSequence)
都是生成CharSequence之后连接的
CharSequence toString(Object part) {
checkNotNull(part);
return (part instanceof CharSequence) ? (CharSequence) part : part.toString();
}
3.2 appendTo
-
参数及返回值
1. Appendable (Appendable , Iteratable)
2. Appendable (Appendable , Iterator)
3. Appendable (Appendable , Object[])
4. StringBuilder (StringBuilder, Iterable)
5. StringBuilder (StringBuilder, Iterator)
6. StringBuilder (StringBuilder, Object[])) -
分析
public <A extends Appendable> A appendTo(A appendable, Iterable<?> parts) throws IOException {
return appendTo(appendable, parts.iterator());
}
调用的还是Appendable appendTo(Appendable , Iterator)方法
大致是一个parts一个separator的方式
public <A extends Appendable> A appendTo(A appendable, Iterator<?> parts) throws IOException {
checkNotNull(appendable);
if (parts.hasNext()) {
appendable.append(toString(parts.next()));
while (parts.hasNext()) {
appendable.append(separator);
appendable.append(toString(parts.next()));
}
}
return appendable;
}
- append效果演示
public static void main(String[] args) {
Joiner joiner = Joiner.on("; ");
StringBuilder sb = new StringBuilder("----");
List<String> list = Lists.newArrayList("a","b","c","d");
sb = joiner.appendTo(sb, list);
System.out.println(sb.toString());
}
输出：----a; b; c; d
3.3 withKeyValueSeparator
-
内部类
MapJoiner -
属性
private final Joiner joiner;
private final String keyValueSeparator; -
方法
1. Appendable (Appendable, Map<?, ?> map))
2. StringBuilder (StringBuilder, Map<?, ?> map))
public <A extends Appendable> A appendTo(A appendable, Iterator<? extends Entry<?, ?>> parts)
throws IOException {
checkNotNull(appendable);
if (parts.hasNext()) {
Entry<?, ?> entry = parts.next();
appendable.append(joiner.toString(entry.getKey()));
appendable.append(keyValueSeparator);
appendable.append(joiner.toString(entry.getValue()));
while (parts.hasNext()) {
appendable.append(joiner.separator);
Entry<?, ?> e = parts.next();
appendable.append(joiner.toString(e.getKey()));
appendable.append(keyValueSeparator);
appendable.append(joiner.toString(e.getValue()));
}
}
return appendable;
}
- withKeyValueSeparator方法,能够返回MapJoiner,在这个方法中传入keyValueSeparator
MapJoiner中，只有在这个方法中传入keyValueSeparator起作用
public MapJoiner withKeyValueSeparator(String keyValueSeparator) {
return new MapJoiner(this, keyValueSeparator);
}
- MapJoiner效果演示：
Map<String, Integer> map = Maps.newHashMap();
map.put("a",1);
map.put("b",2);
map.put("c",3);
StringBuilder sb2 = new StringBuilder("----");
sb2 = joiner.withKeyValueSeparator("+").appendTo(sb2, map);
System.out.println(sb2.toString());
输出：----a+1; b+2; c+3
3.4 join
- 具有四种参数，返回都是String
public final String join(Iterable<?> parts)
public final String join(Iterator<?> parts)
public final String join(Object[] parts)
public final String join(@Nullable Object first, @Nullable Object second, Object... rest)
- 最终都是调用如下的方法：使用StringBuiler构造
public final String join(Iterator<?> parts) {
return appendTo(new StringBuilder(), parts).toString();
}
3.5 useForNull和skipNulls-构造自己时，覆盖自己的某些方法
- 如果是null会抛异常
- useForNull重写了toString，useForNull，skipNulls方法
public Joiner useForNull(final String nullText) {
checkNotNull(nullText);
return new Joiner(this) {
@Override
CharSequence toString(@Nullable Object part) {
return (part == null) ? nullText : Joiner.this.toString(part);
}
@Override
public Joiner useForNull(String nullText) {
throw new UnsupportedOperationException("already specified useForNull");
}
@Override
public Joiner skipNulls() {
throw new UnsupportedOperationException("already specified useForNull");
}
};
}
- skipNulls重写了toString，useForNull，skipNulls方法
public Joiner skipNulls() {
return new Joiner(this) {
@Override
public <A extends Appendable> A appendTo(A appendable, Iterator<?> parts) throws IOException {
checkNotNull(appendable, "appendable");
checkNotNull(parts, "parts");
while (parts.hasNext()) {
Object part = parts.next();
if (part != null) {
appendable.append(Joiner.this.toString(part));
break;
}
}
while (parts.hasNext()) {
Object part = parts.next();
if (part != null) {
appendable.append(separator);
appendable.append(Joiner.this.toString(part));
}
}
return appendable;
}
@Override
public Joiner useForNull(String nullText) {
throw new UnsupportedOperationException("already specified skipNulls");
}
@Override
public MapJoiner withKeyValueSeparator(String kvs) {
throw new UnsupportedOperationException("can't use .skipNulls() with maps");
}
};
}
iterable
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];
}
}
};
}
浙公网安备 33010602011771号