java一对多映射怎么配置

在Java中，一对多映射可以使用集合来实现。常见的一对多映射关系有两种方式：List和Map。

使用List实现一对多映射：

public class OneToManyMapping {
    private List<ManyEntity> manyList;

    // 构造方法
    public OneToManyMapping() {
        manyList = new ArrayList<>();
    }

    // 添加多个实体到列表中
    public void addManyEntity(ManyEntity manyEntity) {
        manyList.add(manyEntity);
    }

    // 获取所有多个实体
    public List<ManyEntity> getManyList() {
        return manyList;
    }
}

public class ManyEntity {
    private String name;

    // 构造方法
    public ManyEntity(String name) {
        this.name = name;
    }

    // 获取实体名称
    public String getName() {
        return name;
    }
}

// 使用示例
OneToManyMapping oneToManyMapping = new OneToManyMapping();
oneToManyMapping.addManyEntity(new ManyEntity("Entity 1"));
oneToManyMapping.addManyEntity(new ManyEntity("Entity 2"));

List<ManyEntity> manyList = oneToManyMapping.getManyList();
for (ManyEntity manyEntity : manyList) {
    System.out.println(manyEntity.getName());
}

使用Map实现一对多映射：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class OneToManyMapping {
    private Map<String, List<ManyEntity>> manyMap;

    // 构造方法
    public OneToManyMapping() {
        manyMap = new HashMap<>();
    }

    // 添加多个实体到映射中
    public void addManyEntity(String key, ManyEntity manyEntity) {
        if (manyMap.containsKey(key)) {
            manyMap.get(key).add(manyEntity);
        } else {
            List<ManyEntity> manyList = new ArrayList<>();
            manyList.add(manyEntity);
            manyMap.put(key, manyList);
        }
    }

    // 获取指定key的多个实体
    public List<ManyEntity> getManyEntities(String key) {
        return manyMap.get(key);
    }
}

public class ManyEntity {
    private String name;

    // 构造方法
    public ManyEntity(String name) {
        this.name = name;
    }

    // 获取实体名称
    public String getName() {
        return name;
    }
}

// 使用示例
OneToManyMapping oneToManyMapping = new OneToManyMapping();
oneToManyMapping.addManyEntity("Key 1", new ManyEntity("Entity 1"));
oneToManyMapping.addManyEntity("Key 1", new ManyEntity("Entity 2"));
oneToManyMapping.addManyEntity("Key 2", new ManyEntity("Entity 3"));

List<ManyEntity> manyList1 = oneToManyMapping.getManyEntities("Key 1");
for (ManyEntity manyEntity : manyList1) {
    System.out.println(manyEntity.getName());
}

List<ManyEntity> manyList2 = oneToManyMapping.getManyEntities("Key 2");
for (ManyEntity manyEntity : manyList2) {
    System.out.println(manyEntity.getName());
}

以上是两种常见的一对多映射的配置方式。具体选择哪种方式取决于实际需求和使用场景。

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