匿名内部类与 lambda 表达式

2021-10-28

今天看别人的代码，创建一个 bean 没看懂，只看出来用了 lambda 表达式。我有几个疑惑：

1. 这个方法只注入了 jwtTokenGenerator ，那 request, response, authentication 这几个参数是谁传的？
2. 点进 AuthenticationSuccessHandler 看到里面定义了一个 void onAuthenticationSuccess(HttpServletRequest var1, HttpServletResponse var2, Authentication var3)，参数列表与上面的一致，说明这段代码实现了 onAuthenticationSuccess()。但这里明显是 return 一个 AuthenticationSuccessHandler 对象啊，onAuthenticationSuccess() 又没有返回值，为啥可以这么写呢？
3. 知道了通过这段代码可以 new 一个 AuthenticationSuccessHandler ，那什么情况下可以模仿他这样子写呢？

• Lambda 规定接口中只能有一个需要被实现的方法

lambda 表达式写法

@Bean
public AuthenticationSuccessHandler authenticationSuccessHandler(JwtTokenGenerator jwtTokenGenerator) {
    return (request, response, authentication) -> {
        if (response.isCommitted()) {
            log.debug("Response has already been committed");
            return;
        }
        Map<String, Object> map = new HashMap<>(5);
        map.put("time", LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
        map.put("flag", "success_login");
        User principal = (User) authentication.getPrincipal();
 
        String username = principal.getUsername();
        Collection<GrantedAuthority> authorities = principal.getAuthorities();
        Set<String> roles = new HashSet<>();
        if (CollectionUtil.isNotEmpty(authorities)) {
            for (GrantedAuthority authority : authorities) {
                String roleName = authority.getAuthority();
                roles.add(roleName);
            }
        }
 
        JwtTokenPair jwtTokenPair = jwtTokenGenerator.jwtTokenPair(username, roles, null);
 
        map.put("access_token", jwtTokenPair.getAccessToken());
        map.put("refresh_token", jwtTokenPair.getRefreshToken());
 
        ResponseUtil.responseJsonWriter(response, RestBody.okData(map, "登录成功"));
    };
}

匿名内部类的写法

@Bean
public AuthenticationSuccessHandler authenticationSuccessHandler(JwtTokenGenerator jwtTokenGenerator) {
    return new AuthenticationSuccessHandler() {
        @Override
        public void onAuthenticationSuccess(HttpServletRequest request, HttpServletResponse response, Authentication authentication) throws IOException, ServletException {
            if (response.isCommitted()) {
                log.debug("Response has already been committed");
                return;
            }
            Map<String, Object> map = new HashMap<>(5);
            map.put("time", LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
            map.put("flag", "success_login");
            User principal = (User) authentication.getPrincipal();
 
            String username = principal.getUsername();
            Collection<GrantedAuthority> authorities = principal.getAuthorities();
            Set<String> roles = new HashSet<>();
            if (CollectionUtil.isNotEmpty(authorities)) {
                for (GrantedAuthority authority : authorities) {
                    String roleName = authority.getAuthority();
                    roles.add(roleName);
                }
            }
 
            JwtTokenPair jwtTokenPair = jwtTokenGenerator.jwtTokenPair(username, roles, null);
 
            map.put("access_token", jwtTokenPair.getAccessToken());
            map.put("refresh_token", jwtTokenPair.getRefreshToken());
 
            ResponseUtil.responseJsonWriter(response, RestBody.okData(map, "登录成功"));
        }
    };
}

Reference

Java 匿名内部类与 Lambda 表达式