java.lang.IllegalArgumentException: There is no PasswordEncoder mapped for the id "null"报错

出现问题的原因：

　　内存用户验证时，Spring boot 2.0.1引用的security 依赖是 spring security 5.X版本，此版本需要提供一个PasswordEncorder的实例，否则后台汇报错误：
java.lang.IllegalArgumentException: There is no PasswordEncoder mapped for the id "null"
并且页面毫无响应。

解决方法：

创建PasswordEncorder的实现类MyPasswordEncoder。

代码一：

 package com.mmall.demo;

 import org.springframework.security.crypto.password.PasswordEncoder;

 public class MyPasswordEncoder implements PasswordEncoder {
     @Override
     public String encode(CharSequence rawPassword) {
         return rawPassword.toString();
     }

     @Override
     public boolean matches(CharSequence rawPassword, String encodedPassword) {
         return encodedPassword.equals(rawPassword);
     }
 }

代码二：

 package com.mmall.demo;

 import org.springframework.context.annotation.Configuration;
 import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
 import org.springframework.security.config.annotation.web.builders.HttpSecurity;
 import org.springframework.security.config.annotation.web.builders.WebSecurity;
 import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
 import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;

 @Configuration
 @EnableWebSecurity
 public class SpringSecurityConfig extends WebSecurityConfigurerAdapter {

     @Override
     protected void configure(AuthenticationManagerBuilder auth) throws Exception {
         auth.inMemoryAuthentication().
                 passwordEncoder(new MyPasswordEncoder()).
                 withUser("admin").password("123456").roles("ADMIN");
     }

     @Override
     protected void configure(HttpSecurity http) throws Exception {
        http.authorizeRequests()
                .antMatchers("/").permitAll()
                .anyRequest().authenticated()
                .and()
                .logout().permitAll()
                .and()
                .formLogin();
        http.csrf().disable();
     }

     @Override
     public void configure(WebSecurity web) throws Exception {
         web.ignoring().antMatchers("/js/**","/css/**","/image/**");
     }

 }