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优化：基于阿里巴巴 Java 开发手册(黄山版)优化部分空集合处理

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1.编程规约>集合处理>第7条：（个人理解：emptyList() 固然可以减少资源浪费，但未来由于不确定的需求变更，一旦增删元素必然会引发异常）
【强制】Collections 类返回的对象，如：emptyList() / singletonList() 等都是 immutable list，不可
对其进行添加或者删除元素的操作。
反例：如果查询无结果，返回 Collections.emptyList() 空集合对象，调用方一旦在返回的集合中进行了添加元素的操
作，就会触发 UnsupportedOperationException 异常。
2.编程规约>集合处理>第17条：
【推荐】集合初始化时，指定集合初始值大小。
说明：HashMap 使用构造方法 HashMap(int initialCapacity) 进行初始化时，如果暂时无法确定集合大小，那么指
定默认值（16）即可。
正例：initialCapacity = (需要存储的元素个数 / 负载因子) + 1。注意负载因子（即 loaderfactor）默认为 0.75，如果
暂时无法确定初始值大小，请设置为 16（即默认值）。
反例：HashMap 需要放置 1024 个元素，由于没有设置容量初始大小，随着元素增加而被迫不断扩容，resize() 方法
总共会调用 8 次，反复重建哈希表和数据迁移。当放置的集合元素个数达千万级时会影响程序性能。
This commit is contained in:
Charles7c 2023-03-03 23:41:01 +08:00
parent dc751fc3ec
commit 6da85463c9
8 changed files with 21 additions and 22 deletions
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6
continew-admin-common/src/main/java/top/charles7c/cnadmin/common/base/BaseServiceImpl.java
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@ -17,8 +17,8 @@
package top.charles7c.cnadmin.common.base;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;
@ -104,7 +104,7 @@ public abstract class BaseServiceImpl<M extends BaseMapper<T>, T, V, D, Q, C ext
public List<Tree<Long>> tree(Q query, SortQuery sortQuery, boolean isSimple) {
List<V> list = this.list(query, sortQuery);
if (CollUtil.isEmpty(list)) {
return Collections.emptyList();
return new ArrayList<>(0);
}
// 如果构建简单树结构，则不包含基本树结构之外的扩展字段
@ -205,7 +205,7 @@ public abstract class BaseServiceImpl<M extends BaseMapper<T>, T, V, D, Q, C ext
queryWrapper.orderBy(order != null, order.isAscending(), StrUtil.toUnderlineCase(order.getProperty()));
}
List<T> entityList = baseMapper.selectList(queryWrapper);
return CollUtil.isNotEmpty(entityList) ? BeanUtil.copyToList(entityList, targetClass) : Collections.emptyList();
return BeanUtil.copyToList(entityList, targetClass);
}
/**

5
continew-admin-common/src/main/java/top/charles7c/cnadmin/common/constant/CharConsts.java
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@ -34,4 +34,9 @@ public class CharConsts implements CharPool {
* 分号
*/
public static final String SEMICOLON = ";";
/**
* 空字符串
*/
public static final String EMPTY = "";
}

2
continew-admin-common/src/main/java/top/charles7c/cnadmin/common/model/vo/PageDataVO.java
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@ -120,7 +120,7 @@ public class PageDataVO<V> {
int fromIndex = (page - 1) * size;
int toIndex = page * size + size;
if (fromIndex > list.size()) {
pageDataVO.setList(new ArrayList<>());
pageDataVO.setList(new ArrayList<>(0));
} else if (toIndex >= list.size()) {
pageDataVO.setList(list.subList(fromIndex, list.size()));
} else {

4
continew-admin-common/src/main/java/top/charles7c/cnadmin/common/util/MailUtils.java
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@ -18,8 +18,8 @@ package top.charles7c.cnadmin.common.util;
import java.io.File;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import javax.mail.MessagingException;
@ -229,7 +229,7 @@ public class MailUtils {
*/
private static List<String> splitAddress(String addresses) {
if (StrUtil.isBlank(addresses)) {
return Collections.emptyList();
return new ArrayList<>(0);
}
List<String> result;

6
continew-admin-common/src/main/java/top/charles7c/cnadmin/common/util/StreamUtils.java
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@ -24,10 +24,10 @@ import java.util.stream.Collectors;
import lombok.AccessLevel;
import lombok.NoArgsConstructor;
import org.apache.commons.lang3.StringUtils;
import cn.hutool.core.collection.CollUtil;
import top.charles7c.cnadmin.common.constant.CharConsts;
/**
* Stream 工具类
*
@ -52,7 +52,7 @@ public class StreamUtils {
*/
public static <E> String join(Collection<E> collection, Function<E, String> function, CharSequence delimiter) {
if (CollUtil.isEmpty(collection)) {
return StringUtils.EMPTY;
return CharConsts.EMPTY;
}
return collection.stream().map(function).filter(Objects::nonNull).collect(Collectors.joining(delimiter));
}

4
continew-admin-common/src/main/java/top/charles7c/cnadmin/common/util/TreeUtils.java
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@ -16,7 +16,7 @@
package top.charles7c.cnadmin.common.util;
import java.util.Collections;
import java.util.ArrayList;
import java.util.List;
import lombok.AccessLevel;
@ -79,7 +79,7 @@ public class TreeUtils {
*/
public static <T, E> List<Tree<E>> build(List<T> list, TreeNodeConfig treeNodeConfig, NodeParser<T, E> nodeParser) {
if (CollUtil.isEmpty(list)) {
return Collections.emptyList();
return new ArrayList<>(0);
}
E parentId = (E)ReflectUtil.getFieldValue(list.get(0), treeNodeConfig.getParentIdKey());
return TreeUtil.build(list, parentId, treeNodeConfig, nodeParser);

4
continew-admin-system/src/main/java/top/charles7c/cnadmin/system/service/impl/RoleMenuServiceImpl.java
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@ -16,7 +16,7 @@
package top.charles7c.cnadmin.system.service.impl;
import java.util.Collections;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
@ -60,7 +60,7 @@ public class RoleMenuServiceImpl implements RoleMenuService {
@Override
public List<Long> listMenuIdByRoleIds(List<Long> roleIds) {
if (CollUtil.isEmpty(roleIds)) {
return Collections.emptyList();
return new ArrayList<>(0);
}
return roleMenuMapper.selectMenuIdsByRoleIds(roleIds);
}

12
continew-admin-system/src/main/java/top/charles7c/cnadmin/system/service/impl/RoleServiceImpl.java
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@ -16,7 +16,7 @@
package top.charles7c.cnadmin.system.service.impl;
import java.util.Collections;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
@ -141,7 +141,7 @@ public class RoleServiceImpl extends BaseServiceImpl<RoleMapper, RoleDO, RoleVO,
List<Long> menuIds = list.stream().map(MenuVO::getMenuId).collect(Collectors.toList());
detailVO.setMenuIds(menuIds);
} else {
detailVO.setMenuIds(roleMenuService.listMenuIdByRoleIds(Collections.singletonList(roleId)));
detailVO.setMenuIds(roleMenuService.listMenuIdByRoleIds(CollUtil.newArrayList(roleId)));
}
detailVO.setDeptIds(roleDeptService.listDeptIdByRoleId(roleId));
}
@ -150,7 +150,7 @@ public class RoleServiceImpl extends BaseServiceImpl<RoleMapper, RoleDO, RoleVO,
@Override
public List<LabelValueVO<Long>> buildDict(List<RoleVO> list) {
if (CollUtil.isEmpty(list)) {
return Collections.emptyList();
return new ArrayList<>(0);
}
return list.stream().map(r -> new LabelValueVO<>(r.getRoleName(), r.getRoleId())).collect(Collectors.toList());
}
@ -158,9 +158,6 @@ public class RoleServiceImpl extends BaseServiceImpl<RoleMapper, RoleDO, RoleVO,
@Override
public List<String> listRoleNamesByRoleIds(List<Long> roleIds) {
List<RoleDO> roleList = super.lambdaQuery().select(RoleDO::getRoleName).in(RoleDO::getRoleId, roleIds).list();
if (CollUtil.isEmpty(roleList)) {
return Collections.emptyList();
}
return roleList.stream().map(RoleDO::getRoleName).collect(Collectors.toList());
}
@ -168,9 +165,6 @@ public class RoleServiceImpl extends BaseServiceImpl<RoleMapper, RoleDO, RoleVO,
public Set<String> listRoleCodesByUserId(Long userId) {
List<Long> roleIds = userRoleService.listRoleIdsByUserId(userId);
List<RoleDO> roleList = super.lambdaQuery().select(RoleDO::getRoleCode).in(RoleDO::getRoleId, roleIds).list();
if (CollUtil.isEmpty(roleList)) {
return Collections.emptySet();
}
return roleList.stream().map(RoleDO::getRoleCode).collect(Collectors.toSet());
}
}