如何在注入TableNameServiceImpl时自动传递OracleService的@Value字段？

我有一个使用tableName变量的TableNameService接口，其实现类为TableNameServiceImpl：

public interface TableNameService {
    void printName();
}

@Service
public class TableNameServiceImpl implements TableNameService{
     @Override
     public void printName() {
          System.out.println(tableName);
     }
}

我将该接口注入到OracleService等服务中，并在这些服务中通过@Value注解初始化tableName字段，示例如下：

@Service
public class OracleService {
     private TableNameService service; 
     @Value("${tableName}")
     private String tableName;

    public void print() {
         service.printName();
    }
}

请问如何在注入TableNameServiceImpl时，将OracleService中的tableName字段自动传递过去，无需在方法参数中传递或手动设置？

1. 原型作用域+构造注入传递值 #

核心思路是让TableNameServiceImpl每次被获取时生成新实例，通过构造方法传入调用方的tableName：

首先修改TableNameServiceImpl，添加构造方法并设置原型作用域：

@Service
@Scope("prototype") // 标记为原型作用域，每次获取创建新实例
public class TableNameServiceImpl implements TableNameService{
     private final String tableName;

     // 构造注入tableName
     public TableNameServiceImpl(String tableName) {
         this.tableName = tableName;
     }

     @Override
     public void printName() {
          System.out.println(tableName);
     }
}

然后在OracleService中用ObjectProvider获取原型实例并传入当前的tableName：

@Service
public class OracleService {
     private final ObjectProvider<TableNameService> tableNameServiceProvider; 
     @Value("${tableName}")
     private String tableName;

     // 构造注入ObjectProvider
     public OracleService(ObjectProvider<TableNameService> tableNameServiceProvider) {
         this.tableNameServiceProvider = tableNameServiceProvider;
     }

    public void print() {
         // 获取新实例并传入当前tableName
         TableNameService service = tableNameServiceProvider.getObject(tableName);
         service.printName();
    }
}

2. ThreadLocal线程上下文传递值 #

如果希望保持TableNameServiceImpl的单例特性，可以用ThreadLocal在调用链中传递tableName：

修改TableNameServiceImpl，添加ThreadLocal存储和清理方法：

@Service
public class TableNameServiceImpl implements TableNameService{
     private static final ThreadLocal<String> TABLE_NAME_HOLDER = new ThreadLocal<>();

     // 设置当前线程的tableName
     public void setTableName(String tableName) {
         TABLE_NAME_HOLDER.set(tableName);
     }

     @Override
     public void printName() {
          System.out.println(TABLE_NAME_HOLDER.get());
     }

     // 清理ThreadLocal，避免内存泄漏
     public void clearTableName() {
         TABLE_NAME_HOLDER.remove();
     }
}

在OracleService中调用前设置值，调用后清理：

@Service
public class OracleService {
     private final TableNameService service; 
     @Value("${tableName}")
     private String tableName;

     public OracleService(TableNameService service) {
         this.service = service;
     }

    public void print() {
         try {
             service.setTableName(tableName);
             service.printName();
         } finally {
             service.clearTableName(); // 必须清理，防止线程复用导致值混乱
         }
    }
}

3. 依赖tableName提供者接口 #

定义一个统一的TableNameProvider接口，让所有调用TableNameService的服务实现该接口，然后TableNameServiceImpl依赖这个接口获取值：

先定义提供者接口：

public interface TableNameProvider {
    String getTableName();
}

修改OracleService实现该接口：

@Service
public class OracleService implements TableNameProvider {
     private final TableNameService service; 
     @Value("${tableName}")
     private String tableName;

     public OracleService(TableNameService service) {
         this.service = service;
     }

    public void print() {
         service.printName();
    }

    @Override
    public String getTableName() {
        return tableName;
    }
}

最后修改TableNameServiceImpl注入TableNameProvider：

@Service
public class TableNameServiceImpl implements TableNameService{
     private final TableNameProvider tableNameProvider;

     public TableNameServiceImpl(TableNameProvider tableNameProvider) {
         this.tableNameProvider = tableNameProvider;
     }

     @Override
     public void printName() {
          System.out.println(tableNameProvider.getTableName());
     }
}

内容的提问来源于stack exchange，提问作者AbrA