个人常用语句笔记-Java

基础篇

判断不为空

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import org.apache.commons.lang3.StringUtils;
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StringUtils.isNotBlank(searchText)

try-with-resources

JDK1.7的新语法，这种try语句可以自动执行资源关闭过程，无需再在finally中显式关闭流。只有所有实现AutoCloseable接口的类的对象才可以由这种带资源的try语句进行管理。从JDK7开始，Closeable扩展了AutoCloseable。因此，在JDK7中，所有实现了Closeable接口的类也都实现了AutoCloseable接口。

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try (FileInputStream fis = new FileInputStream("windcoer_com.txt")) {
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  .....
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}

抛出异常

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throw new AuthenticatException("not-the-owner");
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throw new BusinessException("needed-login");

JPA

@PageableDefault

默认排序

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@PageableDefault(direction=Direction.DESC,sort={"displayOrder"}) Pageable pageable

条件查询

涉及翻页、动态查询、字符串小写化后模糊查询

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import org.springframework.data.domain.Page;
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import org.springframework.data.domain.Pageable;
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public Page<Award> allAwards(Award award,String searchText,Pageable pageable){
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    return super.findAllWithDataRule((root,query,cb)->{
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        Predicate predicate = cb.equal(root.get("isDeleted"), false);
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        predicate = cb.and(predicate,cb.equal(root.get("activity").get("id"), ugcAward.getActivity().getId()));
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        if(StringUtils.isNotBlank(searchText)) {
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            Predicate predicateOr = cb.or(cb.like(cb.lower(root.get("createdBy").get("username")), "%"+StringUtils.trim(searchText).toLowerCase()+"%"),
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            cb.like(cb.lower(root.get("createdBy").get("displayName")), "%"+StringUtils.trim(searchText).toLowerCase()+"%"));
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            predicate = cb.and(predicate,predicateOr);
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        }
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        return predicate;
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    }, pageable);
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}

多表联查

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Subquery<Long> subquery = query.subquery(Long.class);
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  Root<CategoryTreeXref> cateXrefRoot = subquery.from(CategoryTreeXref.class);
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  subquery.select(cateXrefRoot.get("childId"));
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  subquery.where(cb.equal(cateXrefRoot.get("parentId"), caseInfo.getCategory().getId()));
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  predicate = cb.and(predicate,cb.in(root.get("category").get("id")).value(subquery));

虚拟列（@Formula）

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import org.hibernate.annotations.Formula;
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@Formula("(select count(distinct ae.user_id )  from activity_enrollment ae where ae.activity_id = id and ae.is_deleted = 0)")
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  private Long enrollmentCount;

持久化前自动赋值（@PrePersist）

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import javax.persistence.PrePersist;
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@PrePersist
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public void preInsert() {
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    if(this.box == null) {
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        Box box = new Box();
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        this.setBox(box);
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    }
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}

Mybatis

${}-属性property

不同的属性值通过包含的实例变化. 属性值也可以被用在 include 元素的 refid 属性里或者 include 内部语句中，例如：

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<sql id="sometable">
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  ${prefix}Table
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</sql>
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<sql id="someinclude">
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  from
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    <include refid="${include_target}"/>
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</sql>
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<select id="select" resultType="map">
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  select
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    field1, field2, field3
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  <include refid="someinclude">
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    <property name="prefix" value="Some"/>
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    <property name="include_target" value="sometable"/>
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  </include>
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</select>

当一段sql语句仅某些几个字段等不同时，为了重用sql语句，可用此方式解决。 Mapper XML 文件

模糊查询

MySQL

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lower(name) like  concat('%',lower(#{course.name}),'%')

Oracle

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lower(name) like  '%'||lower(#{course.name})||'%'