StringJoiner是Java8新出的一个类,用于构造由分隔符分隔的字符序列,并可选择性地从提供的前缀开始和以提供的后缀结尾。省的我们开发人员再次通过StringBuffer或者StingBuilder拼接。
源码
package java.util;
public class StringJoiner {
private final String prefix; //前缀
private final String delimiter;//间隔符
private final String suffix;//后缀
private StringBuilder value;//值
private String emptyValue;//空值
/**
* @Description 默认前缀和后缀为"",重载调用
*/
public StringJoiner(CharSequence delimiter) {
this(delimiter, "", "");
}
/**
* @Description 设置间隔符、前缀、后缀
*/
public StringJoiner(CharSequence delimiter,
CharSequence prefix,
CharSequence suffix) {
//间隔符,前缀和后缀判断是否为null,null将抛出异常
Objects.requireNonNull(prefix, "The prefix must not be null");
Objects.requireNonNull(delimiter, "The delimiter must not be null");
Objects.requireNonNull(suffix, "The suffix must not be null");
// make defensive copies of arguments
this.prefix = prefix.toString();
this.delimiter = delimiter.toString();
this.suffix = suffix.toString();
this.emptyValue = this.prefix + this.suffix;
}
/**
* @Description 设置空值,检查是否为null
*/
public StringJoiner setEmptyValue(CharSequence emptyValue) {
this.emptyValue = Objects.requireNonNull(emptyValue,
"The empty value must not be null").toString();
return this;
}
/**
* @Description toString()
*/
@Override
public String toString() {
if (value == null) {
return emptyValue;
} else {
if (suffix.equals("")) {
return value.toString();
} else {
int initialLength = value.length();
String result = value.append(suffix).toString();
// reset value to pre-append initialLength
value.setLength(initialLength);
return result;
}
}
}
/**
* @Description 添加
*/
public StringJoiner add(CharSequence newElement) {
prepareBuilder().append(newElement);
return this;
}
/**
* @Description 合并StringJoiner
*/
public StringJoiner merge(StringJoiner other) {
Objects.requireNonNull(other);
if (other.value != null) {
final int length = other.value.length();
// lock the length so that we can seize the data to be appended
// before initiate copying to avoid interference, especially when
// merge 'this'
StringBuilder builder = prepareBuilder();
builder.append(other.value, other.prefix.length(), length);
}
return this;
}
private StringBuilder prepareBuilder() {
if (value != null) {
value.append(delimiter);
} else {
value = new StringBuilder().append(prefix);
}
return value;
}
public int length() {
// Remember that we never actually append the suffix unless we return
// the full (present) value or some sub-string or length of it, so that
// we can add on more if we need to.
return (value != null ? value.length() + suffix.length() :
emptyValue.length());
}
}
使用
package com.example.demo.test;
import java.util.StringJoiner;
/**
* @Author gett
* @Date 2021/12/29 10:47
* @Description StringBuilder拼接字符串的封装处理
*/
public class StringJoinerTest {
public static void main(String[] args) {
StringJoiner stringJoiner = new StringJoiner(",", "[", "]");
stringJoiner.add("张三").add("李四").add("王五");
System.out.println(stringJoiner.toString());
StringJoiner stringJoiner1 = new StringJoiner("..");
stringJoiner1.add("张三").add("李四").add("王五");
System.out.println(stringJoiner1.toString());
StringJoiner merge = stringJoiner1.merge(stringJoiner);
System.out.println(merge.toString());
System.out.println(merge.length());
}
}
输出:
[张三,李四,王五]
张三…李四…王五
张三…李四…王五…张三,李四,王五
20