使用Java代码实现jwt单点登录

以下是一个基本的Java代码实现JWT单点登录的示例：

1. 添加依赖

在 Maven 项目中添加以下依赖：

<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt</artifactId>
    <version>0.9.1</version>
</dependency>

2. 生成 JWT Token

import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import java.util.Date;

public class JwtUtils {
    
    private static final String SECRET_KEY = "YOUR_SECRET_KEY";
    private static final long EXPIRATION_TIME = 86400000; // 24小时
    
    public static String generateToken(String username) {
        Date now = new Date();
        Date expiration = new Date(now.getTime() + EXPIRATION_TIME);
        
        return Jwts.builder()
                .setSubject(username)
                .setIssuedAt(now)
                .setExpiration(expiration)
                .signWith(SignatureAlgorithm.HS256, SECRET_KEY)
                .compact();
    }
    
    // 验证 Token 是否有效
    public static boolean validateToken(String token) {
        try {
            Jwts.parser().setSigningKey(SECRET_KEY).parseClaimsJws(token);
            return true;
        } catch(Exception ex) {
            return false;
        }
    }
    
    // 从 Token 中获取用户名
    public static String getUsernameFromToken(String token) {
        return Jwts.parser().setSigningKey(SECRET_KEY).parseClaimsJws(token).getBody().getSubject();
    }
}

3. 验证 JWT Token

在需要验证用户身份的地方，可以使用以下代码验证 JWT Token：

import javax.servlet.http.HttpServletRequest;
import org.springframework.web.filter.OncePerRequestFilter;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.Claims;
import io.jsonwebtoken.SignatureException;

public class JwtAuthenticationFilter extends OncePerRequestFilter {
    
    private static final String SECRET_KEY = "YOUR_SECRET_KEY";
    private static final String TOKEN_PREFIX = "Bearer";
    private static final String HEADER_STRING = "Authorization";
    
    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws ServletException, IOException {
        String header = request.getHeader(HEADER_STRING);
        if(header == null || !header.startsWith(TOKEN_PREFIX)) {
            chain.doFilter(request, response);
            return;
        }
        
        String token = header.replace(TOKEN_PREFIX, "").trim();
        try {
            Claims claims = Jwts.parser().setSigningKey(SECRET_KEY).parseClaimsJws(token).getBody();
            request.setAttribute("username", claims.getSubject());
        } catch(SignatureException ex) {
            response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
            return;
        }
        
        chain.doFilter(request, response);
    }
}

4. 配置 Spring Security

在 Spring Security 配置类中添加以下配置：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.authentication.AuthenticationManager;
import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
import org.springframework.security.config.annotation.method.configuration.EnableGlobalMethodSecurity;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
import org.springframework.security.config.http.SessionCreationPolicy;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
import org.springframework.security.crypto.password.PasswordEncoder;
import org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter;

@Configuration
@EnableWebSecurity
@EnableGlobalMethodSecurity(prePostEnabled = true)
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    
    @Autowired
    private JwtAuthenticationFilter jwtAuthenticationFilter;
    
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.csrf().disable()
            .sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS)
            .and()
            .authorizeRequests()
            .antMatchers("/login").permitAll()
            .anyRequest().authenticated()
            .and()
            .addFilterBefore(jwtAuthenticationFilter, UsernamePasswordAuthenticationFilter.class);
    }
    
    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth.inMemoryAuthentication()
            .withUser("admin").password(passwordEncoder().encode("admin123")).roles("ADMIN");
    }
    
    @Override
    @Bean
    public AuthenticationManager authenticationManagerBean() throws Exception {
        return super.authenticationManagerBean();
    }
    
    @Bean
    public PasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder();
    }
}

以上就是一个基本的Java代码实现JWT单点登录的示例。需要注意的是，SECRET_KEY 应该是一个随机的字符串，不要泄露给其他人。此外，在实际应用中，应该使用数据库或其他存储来保存用户信息，而不是在配置文件中硬编码。