AOP实现分页有什么好处
利用AOP实现分页功能可以达到零代码入侵的目的，只需要在请求方法上传入对应的分页请求数据即可，SQL的编写以及后台业务与分页代码无关。
PageHelper
PageHelper是Mybatis的一款分页插件，利用ThreadLocal实现分页功能。PageHelper先是根据你即将发出的SQL命令获取count值(也就是数据总量)，然后获取当前线程上的线程变量进行分页操作。如果你还没有使用过PageHelper，推荐先去敲个代码体验一下
执行流程
- 使用aop获取controller方法中分页的相关请求数据PageBean
- 将PageBean保存在线程变量中
- 使用aop拦截dao方法，调用PageHelper的分页方法（使用两次aop是因为PageHelper只会对即将执行的SQL语句进行分页，假设你要分页的数据是第二顺序执行，这时候则会导致第一顺序执行的SQL语句被分页，而第二顺序执行的SQL语句相反）
业务内容
获取所有商品信息，并分页
编写ProductMapper.xml
//编写获取全部商品的SQL语句
<select id="selectAllProduct" resultMap="BaseResultMap">
select product_id, product_name, product_price, product_stock, product_type, product_status,product_version
from t_product
</select>
编写ProductMapper.java
public interface ProductMapper {
List<Product> selectAllProduct();
}
编写ProductDao
//PageInfo是PageHelper封装的一个分页信息类，里面存放着详细的分页字段
public interface ProductDao {
PageInfo<Product> selectAllProductWithPage();
}
@Repository
public class ProductDaoImpl extends BaseDao implements ProductDao {
@Autowired
private ProductMapper productMapper;
@Override
public PageInfo<Product> selectAllProductWithPage() {
return new PageInfo<>(productMapper.selectAllProduct());
}
}
编写ProductService
public interface ProductService {
PageInfo getAllProductWithPage();
}
@Service
public class ProductServiceImpl implements ProductService {
@Autowired
private ProductDao productDao;
@Override
public PageInfo getAllProductWithPage() {
return productDao.selectAllProductWithPage();
}
}
PageBean(分页实体类)
public class PageBean<T> {
// 当前页
private Integer currentPage = 1;
// 每页显示的总条数
private Integer pageSize = 10;
// 总条数
private Integer totalNum;
// 是否有下一页
private Integer isMore;
// 总页数
private Integer totalPage;
// 开始索引
private Integer startIndex;
// 分页结果
private List<T> items;
public PageBean() {
super();
}
public PageBean(Integer currentPage, Integer pageSize, Integer totalNum) {
super();
//
this.currentPage = currentPage;
this.pageSize = pageSize;
this.totalNum = totalNum;
this.totalPage = (this.totalNum+this.pageSize-1)/this.pageSize;
this.startIndex = (this.currentPage-1)*this.pageSize;
this.isMore = this.currentPage >= this.totalPage?0:1;
}
public PageBean(Integer currentPage, Integer pageSize) {
this.currentPage = currentPage;
this.pageSize = pageSize;
}
public Integer getCurrentPage() {
return currentPage;
}
public void setCurrentPage(Integer currentPage) {
this.currentPage = currentPage;
}
public Integer getPageSize() {
return pageSize;
}
public void setPageSize(Integer pageSize) {
this.pageSize = pageSize;
}
public Integer getTotalNum() {
return totalNum;
}
public void setTotalNum(Integer totalNum) {
this.totalNum = totalNum;
}
public Integer getIsMore() {
return isMore;
}
public void setIsMore(Integer isMore) {
this.isMore = isMore;
}
public Integer getTotalPage() {
return totalPage;
}
public void setTotalPage(Integer totalPage) {
this.totalPage = totalPage;
}
public Integer getStartIndex() {
return startIndex;
}
public void setStartIndex(Integer startIndex) {
this.startIndex = startIndex;
}
public List<T> getItems() {
return items;
}
public void setItems(List<T> items) {
this.items = items;
}
}
编写Controller
Controller方法中使用了PageBean接收分页参数或者使用restful风格接收参数，这里并没有限制你必须这么接收，不过你怎么接收分页参数的就需要在aop中怎么拦截并获取
@RestController
@RequestMapping("/product")
public class ProductController {
@Autowired
private ProductService productService;
@PostMapping("/all")
public Result getAllProductWithPage(@RequestBody PageBean pageBean) {
PageInfo pageInfo = productService.getAllProductWithPage();
return Result.success(pageInfo);
}
@GetMapping("/all/{currentPage}/{pageSize}")
public Result getAllProduct2WithPage(@PathVariable int currentPage,@PathVariable int pageSize) {
PageInfo pageInfo = productService.getAllProductWithPage();
return Result.success(pageInfo);
}
}
编写PageHelperAOP类
@Component
@Aspect
public class PageHelperAop {
private static final Logger log = LoggerFactory.getLogger(PageHelperAop.class);
private static final ThreadLocal<PageBean> pageBeanContext = new ThreadLocal<>();
//以WithPage结尾的Controller方法都是需要分页的方法
@Before(value = "execution(* com.viu.technology.controller..*.*WithPage(..))")
public void controllerAop(JoinPoint joinPoint) throws Exception {
log.info("正在执行PageHelperAop");
PageBean pageBean =null;
Object[] args = joinPoint.getArgs();
//获取类名
String clazzName = joinPoint.getTarget().getClass().getName();
//获取方法名称
String methodName = joinPoint.getSignature().getName();
//该方法通过反射获取参数列表
Map<String,Object > nameAndArgs = this.getFieldsName(this.getClass(), clazzName, methodName,args);
pageBean=(PageBean) nameAndArgs.get("pageBean");
if (null == pageBean) {
pageBean = new PageBean();
pageBean.setCurrentPage((Integer) nameAndArgs.get("currentPage"));
pageBean.setPageSize((Integer) nameAndArgs.get("pageSize"));
}
//将分页参数放置线程变量中
pageBeanContext.set(pageBean);
}
@Before(value = "execution(* com.viu.technology.dao..*.*WithPage(..))")
public void daoAop(JoinPoint joinPoint) throws Exception {
PageBean pageBean = pageBeanContext.get();
PageHelper.startPage(pageBean.getCurrentPage(), pageBean.getPageSize());
}
private Map<String,Object> getFieldsName(Class cls, String clazzName, String methodName, Object[] args) throws Exception {
Map<String,Object > map=new HashMap<String,Object>();
ClassPool pool = ClassPool.getDefault();
ClassClassPath classPath = new ClassClassPath(cls);
pool.insertClassPath(classPath);
CtClass cc = pool.get(clazzName);
CtMethod cm = cc.getDeclaredMethod(methodName);
MethodInfo methodInfo = cm.getMethodInfo();
CodeAttribute codeAttribute = methodInfo.getCodeAttribute();
LocalVariableAttribute attr = (LocalVariableAttribute) codeAttribute.getAttribute(LocalVariableAttribute.tag);
if (attr == null) {
// exception
}
int pos = Modifier.isStatic(cm.getModifiers()) ? 0 : 1;
for (int i = 0; i < cm.getParameterTypes().length; i++){
map.put( attr.variableName(i + pos),args[i]);
}
return map;
}
}
PostMan测试
请提前导入相关数据
使用JSON请求会自动将json转换为PageBean实体类，请注意json字段名需和实体类保持一致
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异步调用dao导致分页失败方法
由于异步调用导致子线程无法访问主线程的线程变量，导致PageHelper分页失败
所以你就老老实实的传参，然后调用PageHelper.startPage方法吧，哈哈哈，88
public PageInfo asyncGetAllProductWithPage(int currentPage,int pageSize) {
PageHelper.startPage(currentPage, pageSize);
return productDao.selectAllProductWithPage();
}
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