1. 复现问题

今天读取模板文件后，准备替换文件中的占位符，比如${appPageId}，却报出如下错误：

java.util.regex.PatternSyntaxException: Illegal repetition near index 0
${appPageId}
^
	at java.util.regex.Pattern.error(Pattern.java:1955)
	at java.util.regex.Pattern.closure(Pattern.java:3157)
	at java.util.regex.Pattern.sequence(Pattern.java:2134)
	at java.util.regex.Pattern.expr(Pattern.java:1996)
	at java.util.regex.Pattern.compile(Pattern.java:1696)
	at java.util.regex.Pattern.<init>(Pattern.java:1351)
	at java.util.regex.Pattern.compile(Pattern.java:1028)
	at java.lang.String.replaceAll(String.java:2223)
	at org.apache.commons.lang3.StringUtils.replaceAll(StringUtils.java:5324)
	at com.cloud.lowcode.service.AppModelPageService.modelContentPageDetail(AppModelPageService.java:215)
	at com.cloud.lowcode.service.AppModelPageService$$FastClassBySpringCGLIB$$81597048.invoke(<generated>)
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)
	at com.cloud.lowcode.service.AppModelPageService$$EnhancerBySpringCGLIB$$dc8fcaf.modelContentPageDetail(<generated>)
	at com.cloud.lowcode.service.AppPageService.pageContentDetail(AppPageService.java:355)
	at com.cloud.lowcode.service.AppPageService$$FastClassBySpringCGLIB$$debd183b.invoke(<generated>)
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)
	at com.cloud.lowcode.service.AppPageService$$EnhancerBySpringCGLIB$$2e970468.pageContentDetail(<generated>)
	at com.cloud.lowcode.controller.AppPageController.pageContentDetail(AppPageController.java:99)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1063)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:626)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at com.github.xiaoymin.knife4j.spring.filter.SecurityBasicAuthFilter.doFilter(SecurityBasicAuthFilter.java:87)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:114)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:204)
	at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:183)
	at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:358)
	at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:271)
......

即Illegal repetition near index 0。

2. 分析问题

首先给出模拟的源代码，如下所示：

@Test
public void testReplaceAll(){
  String param="appPageId:${appPageId}";
  String s = StringUtils.replaceAll(param,"${appPageId}","202202031223341");
  System.out.println(s);
}

因为使用的是StringUtils.replaceAll方法，而该方法的第二个参数采用的是正则，如下源码所示：

 public static String replaceAll(final String text, final String regex, final String replacement) {
        if (text == null || regex == null|| replacement == null ) {
            return text;
        }
        return text.replaceAll(regex, replacement);
    }

正则需要使用\\双斜杠转义字符：‘$’, ‘(’, ‘)’, ‘*’, ‘+’, ‘.’, ‘[’, ‘]’, ‘?’, ‘\’, ‘^’, ‘{’, ‘}’, ‘|’

3. 解决问题

既然知道了正则需要转义字符，因而代码进行如下修改：

 @Test
  public void testReplaceAll(){
    String param="appPageId:${appPageId}";
    String s = StringUtils.replaceAll(param,"\\$\\{appPageId\\}","202202031223341");
    System.out.println(s);
  }

当然，我们可以不使用StringUtils.replaceAll方法，可以使用StringUtils.replace方法，这样就可以不用转义了，如下代码所示：

 @Test
  public void testReplaceAll(){
    String param="appPageId:${appPageId}";
    String s = StringUtils.replace(param,"${appPageId}","202202031223341");
    System.out.println(s);
  }