第四章：Room数据库直接存储对象（二进制数据，Android面试必问的HashMap
-
获取Cache数据库操作对象
-
@return
*/
public abstract CacheDao getCacheDao();
- 创建缓存数据类（注意一定要序列化Serializable）
package cn.yumakeji.jetpackroomstudy.bean;
import java.io.Serializable;
public class CacheBean implements Serializable {
private String name;
private String title;
private long time;
private String imgUrl;
private String desc;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getImgUrl() {
return imgUrl;
}
public long getTime() {
return time;
}
public void setTime(long time) {
this.time = time;
}
public void setImgUrl(String imgUrl) {
this.imgUrl = imgUrl;
}
public String getDesc() {
return desc;
}
public void setDesc(String desc) {
this.desc = desc;
}
@Override
public String toString() {
return “CacheBean{” +
“name=’” + name + ‘’’ +
“, title=’” + title + ‘’’ +
“, time=” + time +
“, imgUrl=’” + imgUrl + ‘’’ +
“, desc=’” + desc + ‘’’ +
‘}’;
}
}
- 序列化和反序列化工具
package cn.yumakeji.jetpackroomstudy.room;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class RoomManager {
//反序列,把二进制数据转换成java object对象
public static Object toObject(byte[] data) {
ByteArrayInputStream bais = null;
ObjectInputStream ois = null;
try {
bais = new ByteArrayInputStream(data);
ois = new ObjectInputStream(bais);
return ois.readObject();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (bais != null) {
bais.close();
}
if (ois != null) {
ois.close();
}
} catch (Exception ignore) {
ignore.printStackTrace();
}
}
return null;
}
//序列化存储数据需要转换成二进制
public static byte[] toByteArray(T body) {
ByteArrayOutputStream baos = null;
ObjectOutputStream oos = null;
try {
baos = new ByteArrayOutputStream();
oos = new ObjectOutputStream(baos);
oos.writeObject(body);
oos.flush();
return baos.toByteArray();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (baos != null) {
baos.close();
}
if (oos != null) {
oos.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
return new byte[0];
}
}
- 使用
/**
-
增加对象数据库
-
@param view
*/
public void onInsertDataClick(View view) {
for (int i = 0; i < 5; i++) {
CacheBean cacheBean = new CacheBean();
cacheBean.setName(“huang” + i);
cacheBean.setTime(System.currentTimeMillis());
cacheBean.setTitle(“测试数据” + i);
cacheBean.setDesc(“这是偶的描述信息” + i);
cacheBean.setImgUrl(“https://blog.csdn.net/huangxiaoguo1”);
Cache cache = new Cache();
cache.key = cacheBean.getName();
//序列化存储数据需要转换成二进制
cache.data = RoomManager.toByteArray(cacheBean);
RoomDataBase.get().getCacheDao().
insert(cache);
}
}
/**
-
删除对象数据库
-
@param view
*/
public void onDeleteDataClick(View view) {
Cache cache = RoomDataBase.get().getCacheDao().findByKey(“huang2”);
if (cache == null) {
return;
}
RoomDataBase.get().getCacheDao().delete(cache);
}
/**
-
更新对象数据库
-
@param view
*/
public void onUpdataDataClick(View view) {
Cache cache = RoomDataBase.get().getCacheDao().findByKey(“huang3”);
if (cache == null) {
return;
}
CacheBean cacheBean = (CacheBean) RoomManager.toObject(cache.data);
if (cacheBean == null) {
Log.e(“TTT”, “获取到的数据为空”);
return;
}
cacheBean.setTitle(“我被修改了”);
cache.data = RoomManager.toByteArray(cacheBean);
RoomDataBase.get().getCacheDao().update(cache);
}
/**
-
获取所有对象数据
-
@param view
*/
public void onFindAllDataClick(View view) {
List lists = RoomDataBase.get().getCacheDao().findAll();
for (Cache list : lists) {
Log.e(“TTT”, “key:” + list.key + “,data:” + ((CacheBean) RoomManager.toObject(list.data)).toString());
}
}
/**
-
一对一所有对象数据
-
@param view
*/
public void onFindOneDataClick(View view) {
Cache cache = RoomDataBase.get().getCacheDao().findByKey(“huang3”);
@param view
*/
public void onFindAllDataClick(View view) {
List lists = RoomDataBase.get().getCacheDao().findAll();
for (Cache list : lists) {
Log.e(“TTT”, “key:” + list.key + “,data:” + ((CacheBean) RoomManager.toObject(list.data)).toString());
}
}
/**
-
一对一所有对象数据
-
@param view
*/
public void onFindOneDataClick(View view) {
Cache cache = RoomDataBase.get().getCacheDao().findByKey(“huang3”);