MySQL连接被阻塞问题分析与解决方案：从错误到修复的完整指南

Host '124.221.131.191' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'

java.sql.SQLException: null, message from server: 
"Host '124.221.131.191' is blocked because of many connection errors; 
unblock with 'mysqladmin flush-hosts'"

FLUSH HOSTS;

mysqladmin flush-hosts -u root -p

-- 查看当前值
SHOW VARIABLES LIKE 'max_connect_errors';

-- 修改（需重启MySQL或动态调整）
SET GLOBAL max_connect_errors = 1000;

spring:
  datasource:
    url: jdbc:mysql://124.221.131.191:3306/kwan?useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
    username: your_username
    password: your_password
    driver-class-name: com.mysql.cj.jdbc.Driver
    type: com.alibaba.druid.pool.DruidDataSource
    druid:
      initial-size: 5       # 初始连接数
      min-idle: 5           # 最小空闲连接
      max-active: 20        # 最大活跃连接
      max-wait: 60000       # 获取连接超时时间（毫秒）
      validation-query: SELECT 1  # 连接检测SQL
      test-while-idle: true # 空闲时检测连接
      test-on-borrow: false  # 获取连接时不检测（影响性能）
      test-on-return: false  # 归还连接时不检测
      time-between-eviction-runs-millis: 60000 # 检测间隔
      min-evictable-idle-time-millis: 300000    # 最小空闲时间

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.sql.DataSource;

public class UserDao {
    private final DataSource dataSource;

    public UserDao(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    public String getUserNameById(int id) {
        String sql = "SELECT username FROM users WHERE id = ?";
        try (Connection conn = dataSource.getConnection();
             PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setInt(1, id);
            try (ResultSet rs = stmt.executeQuery()) {
                if (rs.next()) {
                    return rs.getString("username");
                }
            }
        } catch (SQLException e) {
            throw new RuntimeException("Failed to query user", e);
        }
        return null;
    }
}

@Bean
public ServletRegistrationBean<StatViewServlet> druidStatViewServlet() {
    ServletRegistrationBean<StatViewServlet> registrationBean = 
        new ServletRegistrationBean<>(new StatViewServlet(), "/druid/*");
    registrationBean.addInitParameter("loginUsername", "admin");
    registrationBean.addInitParameter("loginPassword", "admin");
    return registrationBean;
}

public Connection getConnectionWithRetry(DataSource dataSource, int maxRetries) {
    int retryCount = 0;
    while (retryCount < maxRetries) {
        try {
            return dataSource.getConnection();
        } catch (SQLException e) {
            retryCount++;
            if (retryCount >= maxRetries) {
                throw new RuntimeException("Failed to get connection after " + maxRetries + " retries", e);
            }
            try {
                Thread.sleep(1000); // 1秒后重试
            } catch (InterruptedException ie) {
                Thread.currentThread().interrupt();
                throw new RuntimeException("Interrupted while waiting for retry", ie);
            }
        }
    }
    throw new IllegalStateException("Should not reach here");
}

[mysqld]
max_connections = 200          # 最大连接数
wait_timeout = 28800          # 非交互式连接超时时间（秒）
interactive_timeout = 28800   # 交互式连接超时时间
max_connect_errors = 1000     # 调高连接错误阈值