多对一映射处理：采用分步查询根据员工ID查询员工信息和员工对应的部门信息用Java实现

首先，我们需要建立一个员工信息类和一个部门信息类，代码如下：

public class Employee {
    private int id;
    private String name;
    private String department;

    public Employee(int id, String name, String department) {
        this.id = id;
        this.name = name;
        this.department = department;
    }

    // getter and setter methods
}

public class Department {
    private String name;
    private String location;

    public Department(String name, String location) {
        this.name = name;
        this.location = location;
    }

    // getter and setter methods
}

接下来，我们需要建立一个员工信息和部门信息的映射关系类，代码如下：

public class EmployeeDepartmentMap {
    private Map<Integer, Employee> employeeMap;
    private Map<String, Department> departmentMap;

    public EmployeeDepartmentMap() {
        employeeMap = new HashMap<>();
        departmentMap = new HashMap<>();
        // 假设已经有预先设定的员工信息和部门信息
        employeeMap.put(1, new Employee(1, "Tom", "Finance"));
        employeeMap.put(2, new Employee(2, "Jerry", "Marketing"));
        employeeMap.put(3, new Employee(3, "Bob", "HR"));
        departmentMap.put("Finance", new Department("Finance", "Beijing"));
        departmentMap.put("Marketing", new Department("Marketing", "Shanghai"));
        departmentMap.put("HR", new Department("HR", "Guangzhou"));
    }

    public Employee getEmployeeById(int id) {
        return employeeMap.get(id);
    }

    public Department getDepartmentByEmployee(Employee employee) {
        return departmentMap.get(employee.getDepartment());
    }
}

最后，我们可以在主函数中使用上述类获取员工信息和对应的部门信息，代码如下：

public class Main {
    public static void main(String[] args) {
        EmployeeDepartmentMap map = new EmployeeDepartmentMap();
        Employee employee = map.getEmployeeById(1);
        Department department = map.getDepartmentByEmployee(employee);
        System.out.println("Employee: " + employee.getName() + ", Department: " + department.getName() + ", Location: " + department.getLocation());
    }
}

输出结果为：

Employee: Tom, Department: Finance, Location: Beijing

注意，上述代码只是一个简单的示例，实际情况中需要根据具体需求进行适当的修改。