mybatis 在当前项目中的实际应用及自定义分页的实现
项目中分页代码的解耦
实现目标
实现目标，使用spring 提供的分页相关的类，避免代码中直接使用PageHelper
具体实现
创建自定义PageHelper，并使用spring-data-common提供的具体实现类操作分页
maven 中引入相关依赖
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-commons</artifactId>
<version>2.6.2</version>
</dependency>
public class PageHelper {
//创建分页参数
public static Pageable createPageable(int page, int size ) {
return PageRequest.of(page,size);
}
//创建分页参数
public static Pageable createPageable(int page, int size, Sort sort) {
return PageRequest.of(page,size,sort);
}
public static Page createPage(List content, Pageable pageable, long total) {
return new PageImpl(content,pageable,total);
}
public static Page doSelectPage(Pageable pageable,Select select) {
com.github.pagehelper.Page page = com.github.pagehelper.PageHelper.startPage(pageable.getPageNumber(), pageable.getPageSize()).doSelectPage(() -> select.doSelect());
return createPage(page,pageable,page.getTotal());
}
}
public interface Select {
void doSelect();
}
这样我们在项目中就不直接与pageHelper 打交道了，将代码控制在自定义的 PageHelper 中了。
具体应用
首先我们的controller层面的过滤bean class 统一继承 PagedRequest.class
public class PagedRequest extends Request {
/**
* 页号
*/
private Integer pageNum;
/**
* 单页大小(rows)
*/
private Integer pageSize;
public Integer getPageNum() {
return pageNum;
}
public void setPageNum(Integer pageNum) {
this.pageNum = pageNum;
}
public Integer getPageSize() {
return pageSize;
}
public void setPageSize(Integer pageSize) {
this.pageSize = pageSize;
}
}
到controller层面 因为要调用service，所以转化为 domain对象 我们使用 spring data 提供的 domain Pageable.class
//调用我们自己的工具类创建分页对象
Pageable pageable =
PagingHelper.createPageable(merchantAuditListReq.getPageNum(), merchantAuditListReq.getPageSize());
将 Pageable 对象和 过滤条件对象传递给service方法
Page<MerchantAuditListResultModel> page_result = merchantService.getMerchAuditList(pageable, merchantAuditListParamModel);
service 的方法的返回值必须返回 spring data 提供的domain Page 作为返回值
service 层调用具体的查询语句需要使用mybatis 的分页插件，这里提供了一个工具类 PagingHepler.class
//select 方法有两个参数 1 分页数据 2 具体执行的查询方法
Page<MerchantInfoDetailResult> page = PagingHelper.select(pageable, () ->
custMerchantInfoMapper.getMerchantDetailInfoByExample(merchantInfoParam));
select 方法的具体实现如下，其实还是调用page hepler 的方法来查询分页,获取到数据之后通过 createPage 来创建我们内部流传的Page domain
public static Page select(Pageable pageable, PagingSelector pagingSelector) {
com.github.pagehelper.Page page = PageHelper.startPage(pageable.getPageNumber() + 1, pageable.getPageSize())
.doSelectPage(new PageHelperSelect(pagingSelector));
return createPage(page.getResult(), pageable, page.getTotal());
}
public static Page createPage(List content, Pageable pageable, long total) {
return new PageImpl(content, pageable, total);
}
实体类中枚举的更高实现在MyBatis 中的应用
配置
实现自定义枚举类的 TypeHandler，并将枚举转换的TypeHandler 放入mybatis 的config当中.
public class TypeCodeTypeHandler<E extends Enumerable> extends BaseTypeHandler<E> {
private Class<E> type;
private final Map<Integer, E> enums;
public TypeCodeTypeHandler(Class<E> type) {
if (type == null) {
throw new IllegalArgumentException("type argument cannot be null");
}
/// 是一个 Java 反射 API 方法，用于获取指定枚举类的所有枚举常量。
E[] enumArray = type.getEnumConstants();
Map<Integer, E> enums = new HashMap<Integer, E>();
for (E each : enumArray) {
enums.put(each.getCode(), each);
}
this.type = type;
this.enums = enums;
}
@Override
public void setNonNullParameter(PreparedStatement ps, int i, E parameter,
JdbcType jdbcType) throws SQLException {
ps.setInt(i, parameter.getCode());
}
@Override
public E getNullableResult(ResultSet rs, String columnName)
throws SQLException {
int code = rs.getInt(columnName);
if (rs.wasNull()) {
return null;
} else {
try {
return enums.get(code);
} catch (Exception ex) {
throw new IllegalArgumentException("Cannot convert " + code
+ " to " + type.getSimpleName() + " by code value.", ex);
}
}
}
@Override
public E getNullableResult(ResultSet rs, int columnIndex)
throws SQLException {
int code = rs.getInt(columnIndex);
if (rs.wasNull()) {
return null;
} else {
try {
return enums.get(code);
} catch (Exception ex) {
throw new IllegalArgumentException("Cannot convert " + code
+ " to " + type.getSimpleName() + " by code value.", ex);
}
}
}
@Override
public E getNullableResult(CallableStatement cs, int columnIndex)
throws SQLException {
int code = cs.getInt(columnIndex);
if (cs.wasNull()) {
return null;
} else {
try {
return enums.get(code);
} catch (Exception ex) {
throw new IllegalArgumentException("Cannot convert " + code
+ " to " + type.getSimpleName() + " by code value.", ex);
}
}
}
}
public SqlSessionFactory sqlSessionFactory() {
try {
List<String> packages = Lists.newArrayList();
packages.add("com.kaffatech.mocha.common.lang.type");
//创建对应类型的 TypeHandler
List<TypeHandler> typeHandlers = TypeHandlerUtils.getTypeHandlerByPackages(packages);
bean.setTypeHandlers(typeHandlers.toArray(new TypeHandler[typeHandlers.size()]));
return bean.getObject();
} catch (Exception e) {
throw new IllegalStateException(e);
}
使用
枚举类都需要继承自Enumerable 接口
public enum ConsumeTradeStatus implements Enumerable {
WAIT(0, "待支付"), PROCESSING(2, "支付中"), SUCCESS(3, "支付成功"),FALSE(4,"支付失败"), CLOSE(5, "已失效");
private Integer code;
private String description;
ConsumeTradeStatus(Integer code, String description) {
this.code = code;
this.description = description;
}
@Override
public int getCode() {
return code;
}
@Override
public String getCodeString() {
return name();
}
@Override
public String getDescription() {
return description;
}
}
public interface Enumerable {
/**
* 获取代码
* @return
*/
int getCode();
/**
* 获取字符型代码(一般情况应为枚举name)
* @return
*/
String getCodeString();
/**
* 获取描述
* @return
*/
String getDescription();
}
如果数据库中的字段使用枚举类型，声明为 tinyInt 类型，并在代码生成器那进行属性类型覆盖EntryManualType
<table tableName="accounting_entry_apply">
<columnOverride column="entry_manual_type"
javaType="com.flashfin.flp.ms.domain.accounting.type.EntryManualType"></columnOverride>
<columnOverride column="audit_status"
javaType="com.flashfin.flp.ms.domain.accounting.type.AuditStatus"></columnOverride>
<columnOverride column="deleted" javaType="java.lang.Boolean"></columnOverride>
<columnOverride column="create_time" javaType="java.time.Instant"></columnOverride>
<columnOverride column="update_time" javaType="java.time.Instant"></columnOverride>
<columnOverride column="audit_time" javaType="java.time.Instant"></columnOverride>
</table>
关于这样做的好处
记当前项目中国际化的做法_奋斗的小面包的博客-CSDN博客
扩展
分页原理的实现
常见的分页方式有如下两种
PageHelper.startPage(1, 10);
Page<User> users = (Page<User>) userMapper.selectList("user",null);//也可以是 List<Country> list = countryMapper.selectIf(1);
这种机制的实现原理是在调用PageHelper.start 的时候创建一个Page对象放入threadLocal 中，当mybatis的插件拦截到他时获取threadLocal中的page对象，进行sql的改写，之后讲查询到的结果放入 page 对象之中进行返回，Page是派生自List的，所以这也就是解释了为什么我们使用List 接收或使用Page 进行接收都不会报错的原理。
第二种分页方式如下
Page<Country> page = PageHelper.startPage(1, 10).doSelectPage(new ISelect() {
@Override
public void doSelect() {
countryMapper.selectGroupBy();
}
});
这又是什么机理呢，其实妙处就在于Page对象的提前暴露，当我们在调用调用start 的时候会创建一个page对象，并将该对象放入ThreadLocal当中，并将Page对象返回，这就给我我们机会提前引用，调用select 的时候会执行具体的dao操作，此时就算在plugin 中删除了ThreadLocal的Page的对象，我们外接依旧是有引用的
源码展示
//pagehelper 中
public static <E> Page<E> startPage(int pageNum, int pageSize, boolean count, Boolean reasonable, Boolean pageSizeZero) {
Page<E> page = new Page<E>(pageNum, pageSize, count);
page.setReasonable(reasonable);
page.setPageSizeZero(pageSizeZero);
//当已经执行过orderBy的时候
Page<E> oldPage = getLocalPage();
if (oldPage != null && oldPage.isOrderByOnly()) {
page.setOrderBy(oldPage.getOrderBy());
}
setLocalPage(page);
return page;
}
//Page 中
public <E> Page<E> doSelectPage(ISelect select) {
select.doSelect();
return (Page<E>) this;
}
说了这么久，分页插件的大致机理已经了解了，多说无益我们直接实现一下自定义的分页插件吧
实现自定义分页 插件
@Intercepts(
{
@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}),
@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, CacheKey.class, BoundSql.class}),
}
)
public class PageHelper implements Interceptor {
public static ThreadLocal<Pageable> pageInfos = new ThreadLocal<>();
public static void startPage(int pageNum,int pageSize) {
pageInfos.set(PageRequest.of(pageNum,pageSize));
}
public static Pageable getPage() {
return pageInfos.get();
}
public static void remove() {
pageInfos.remove();
}
@Override
public Object intercept(Invocation invocation) throws Throwable {
try {
MappedStatement mappedStatement = (MappedStatement) invocation.getArgs()[0];
SqlSource sqlSource = mappedStatement.getSqlSource();
BoundSql boundSql;
if (invocation.getArgs().length == 6) {
boundSql = (BoundSql) invocation.getArgs()[5];
} else {
boundSql = mappedStatement.getBoundSql(invocation.getArgs()[1]);
}
Object parameterObject = invocation.getArgs()[1];
//判读是否需要分页,判断的逻辑就是PageHelper 中是否有page信息
Pageable page = PageHelper.getPage();
if (page != null) {
//查询总的total
String sql = boundSql.getSql();
String prefix = "Select count(0) ";
int from = sql.indexOf("from");
String countSql = prefix + sql.substring(from, sql.length());
Executor executor = (Executor) invocation.getTarget();
ResultMap resultMap = new ResultMap.Builder(mappedStatement.getConfiguration(), mappedStatement.getId() + "count", Integer.class, Collections.EMPTY_LIST, true).build();
StaticSqlSource countBoundSql = new StaticSqlSource(mappedStatement.getConfiguration(), countSql, boundSql.getParameterMappings());
MappedStatement countMappedStatement = new MappedStatement.Builder(mappedStatement.getConfiguration(), mappedStatement.getId() + "count", countBoundSql, mappedStatement.getSqlCommandType())
.cache(mappedStatement.getCache())
.databaseId(mappedStatement.getDatabaseId())
.fetchSize(mappedStatement.getFetchSize())
.statementType(mappedStatement.getStatementType())
.resultMaps(Arrays.asList(resultMap)).build();
List<Object> query = executor.query(countMappedStatement,parameterObject,(RowBounds)invocation.getArgs()[2],(ResultHandler)invocation.getArgs()[3]);
int total = (int) query.get(0);
//分页插叙
int pageSize = page.getPageSize();
int pageNumber = page.getPageNumber();
String selectSql = boundSql.getSql();
selectSql = selectSql + " " + "limit " + (pageNumber - 1) * pageSize + "," + pageSize;
BoundSql selectBoundSql = new BoundSql(mappedStatement.getConfiguration(), selectSql, boundSql.getParameterMappings(), boundSql.getParameterObject());
//进行查询操作
Object proceed = executor.query(mappedStatement,parameterObject,(RowBounds)invocation.getArgs()[2],(ResultHandler)invocation.getArgs()[3],(CacheKey) invocation.getArgs()[4],selectBoundSql);
Page ret = new Page(pageNumber, pageSize);
ret.setTotal(total);
ret.addAll((Collection) proceed);
return ret;
}
}catch (Exception e) {
e.printStackTrace();
}
finally {
//清除分页信息
PageHelper.remove();
}
return invocation.proceed();
}
@Override
public Object plugin(Object target) {
return Plugin.wrap(target,this);
}
@Override
public void setProperties(Properties properties) {
}
}
@Configuration
public class PageHelperConfig implements InitializingBean {
@Autowired
private SqlSessionFactory sqlSessionFactory;
public void afterPropertiesSet() throws Exception {
PageHelper interceptor = new PageHelper();
interceptor.setProperties(null);
sqlSessionFactory.getConfiguration().addInterceptor(interceptor);
}
}
ok ok ok 目前先写到这里，本文档持续更新ing
