半角空格 全角空格 不间断空格 通过过滤器解决

半角空格：u0020  英文符号  代码中常用

全角空格：u3000  中文符号  中文文章中常用

不间断空格：u00A0  不间断空格  主要在 office 中使用，让一个单词在结尾处不会换行显示，快捷键 Ctrl + Shift + Space

半角空格和不间断空格肉眼是分辨不出来的，但是程序能够分辨出来。

public class Test {
    public static void main(String[] args) {
        System.err.println("Hellou00A0World");   // Hello World
        System.err.println("Hellou0020World");   // Hello World 常用
        System.err.println("Hellou3000World");   // Hello　World
        String spaceA = " ";  // 不间断空格
        String spaceB = " ";  // 半角空格
        String spaceC = "　";  // 全角空格
        System.err.println(spaceA.equals(spaceB));    // false
        System.err.println(spaceA.equals(spaceC));    // false
        System.err.println(spaceB.equals(spaceC));    // false
        System.err.println("u00A0".equals(spaceA));  // true
        System.err.println("u0020".equals(spaceB));  // true
        System.err.println("u3000".equals(spaceC));  // true
    }
}

 将字符串中的不连续转变成半角空格

String str = "Hellou00A0world"
str = str.replace('u00A0', 'u0020');  // 将不间断空格替换为半角空格 

 在 Java Web 开发中遇到时可通过添加过滤器的方式来解决

过滤器代码如下：

package pathogen.filter;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class SpecialCharacterFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        // 采用 Request 包装类包装 request 的方法，拦截获取参数的方法，替换特殊字符。
        chain.doFilter(new SpecialCharacterRequestWrapper((HttpServletRequest)request), response);  
    }

}

class SpecialCharacterRequestWrapper extends HttpServletRequestWrapper {

    public SpecialCharacterRequestWrapper(HttpServletRequest request) {
        super(request);
    }

    @Override
    public String getParameter(String name) {
        return replaceSpecialCharacter(super.getParameter(name));
    }

    @Override
    public Map<String, String[]> getParameterMap() {
        Map<String, String[]> originalParameters = super.getParameterMap();
        Map<String, String[]> newParameters = new HashMap<>(originalParameters.size());
        // Lambda 表达式 + forEach() 遍历 Map 
        originalParameters.forEach((k, v) -> newParameters.put(k, replaceSpecialCharacter(v)));  // v 的数据类型是 String []
        return newParameters;
    }

    @Override
    public String[] getParameterValues(String name) {
        return replaceSpecialCharacter(super.getParameterValues(name));
    }
    
    private String replaceSpecialCharacter(String str) {
        return str == null ? null : str.replace("u00A0", "u0020");  // 将不连续空格替换为半角空格
    }
    
    private String [] replaceSpecialCharacter(String[] str) {
        if (str == null) {
            return str;
        }
        for (int i = 0; i < str.length; i++) {
            str[i] = replaceSpecialCharacter(str[i]);
        }
        return str;
    }
}

在部署描述符（web.xml）中配置过滤器

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    id="WebApp_ID" version="3.0">
    <servlet>
        <servlet-name>DataEntryServlet</servlet-name>
        <servlet-class>pathogen.controller.DataEntryServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>DataEntryServlet</servlet-name>
        <url-pattern>/entry</url-pattern>
    </servlet-mapping>
    <servlet>
        <display-name>QueryServlet</display-name>
        <servlet-name>QueryServlet</servlet-name>
        <servlet-class>pathogen.controller.QueryServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>QueryServlet</servlet-name>
        <url-pattern>/query</url-pattern>
    </servlet-mapping>
    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>pathogen.controller.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
    <filter>
        <filter-name>SpecialCharacterFilter</filter-name>
        <filter-class>pathogen.filter.SpecialCharacterFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>SpecialCharacterFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>