Java正则表达式过滤并消除非法字符
## 过滤并消除非法字符示例
```java
// 除了字母数字下划线之外的字符为非法字符
Pattern pattern = Pattern.compile("[^a-zA-Z0-9]");
// 指定设置非法字符
// Pattern pattern = Pattern.compile("[@#]");
String str = "123@abc#DEF";
Matcher matcher = pattern.matcher(str);
StringBuffer buffer = new StringBuffer();
// 如果找到非法字符
while (matcher.find()) {
// 如果里面包含非法字符如冒号双引号等，那么就把他们消去，并把非法字符前面的字符放到缓冲区
matcher.appendReplacement(buffer, "");
}
// 将剩余的合法部分添加到缓冲区
matcher.appendTail(buffer);
System.out.println("您的输入为: " + str);
System.out.println("合法的输出为: " + buffer.toString());
```
输出：
```
您的输入为: 123@abc#DEF
合法的输出为: 123abcDEF
```
## 批量替换的示例
```
Pattern p = Pattern.compile("cat");
Matcher m = p.matcher("one cat two cats in the yard");
StringBuffer sb = new StringBuffer();
while (m.find()) {
m.appendReplacement(sb, "dog");
}
m.appendTail(sb);
System.out.println(sb.toString());
```
输出：
```
one dog two dogs in the yard
```