springmvc+jpa实现分页的两种方式

1.工具类

public final class QueryTool {
public static PageRequest buildPageRequest(int pageNumber, int pageSize, String sortType){
Sort sort = null;
if("auto".equals(sortType)) {
sort = new Sort(Direction.DESC, "ctime");
} else {
sort = new Sort(Direction.DESC, "ctime");
}

return new PageRequest(pageNumber, pageSize, sort);
}

public static <T> Specification<T> buildSpecification(Map<String, Object> searchParams, Class<T> domainClass){
Map<String, SearchFilter> filters = SearchFilter.parse(searchParams);
Specification<T> spec = DynamicSpecifications.bySearchFilter(filters.values(), domainClass);
return spec;
}
}

2.Service类（只给出CommentService）

@Service
public class CommentService {
@Autowired
private CommentDao commentDao;

@Transactional
public void addComment(Comment comment) {
if(comment == null) return;
commentDao.save(comment);
}

@Transactional
public Page<Comment> findAllComments(String problemId, PageRequest pageable){
Page<Comment> page = commentDao.findAllCommentsByProblemId(problemId, pageable);
return page;
}
}

3.repository类（problem 和 comment 属于 一对多 的关系）

@Repository
public interface CommentDao extends JpaSpecificationExecutor<Comment>,
PagingAndSortingRepository<Comment, String> {

@Query("select c from Comment c where c.problem.problemid = ?1")
public Page<Comment> findAllCommentsByProblemId(String problemId, Pageable pageable);
}

4.Controller类

　　第一种方式

@Controller
public class ProblemController {

@Autowired
private ProblemService problemService;

@Autowired
private CommentService commentService;

@RequestMapping(value="getCurProblemComments")
@ResponseBody
public String getCurProblemComments(String problemName, @RequestParam(value = "pn", defaultValue = "1") int pageNumber,
@RequestParam(value = "ps", defaultValue = "4") int pageSize,
@RequestParam(value = "sortType", defaultValue = "auto") String sortType){
JSONObject jsono = new JSONObject();
try {
Problem problem = problemService.getProblemByName(problemName);
if(problem == null){
problem = problemService.addProblem(problemName);
}
PageRequest pageRequest = QueryTool.buildPageRequest(pageNumber, pageSize, sortType);
//根据题目的id获取所有的评论
Page<Comment> page = commentService.findAllComments(problem.getProblemid(), pageRequest);
//对 Comment 这个类中的一些字段进行过滤
SimplePropertyPreFilter spp = new SimplePropertyPreFilter();
spp.getExcludes().addAll(Comment.getExcludeString());
jsono.put("success", true);
jsono.put("message", JSON.toJSONString(page, spp));
} catch(Exception e){
e.printStackTrace();
jsono.put("success", false);
jsono.put("message", "inner error.");
}
return jsono.toString();
}
}

　　

　　第二种方式，（懒了，有些内容是放在servic中的。）

　　通过JpaSpecificationExecutor<T> 的Page<T> findAll(Specification<T> spec, Pageable pageable); 方法（按照指定的规格条件）实现分页查询。

public String getCurProblemComments(@RequestParam(value = "pn", defaultValue = "1") int pageNumber,
@RequestParam(value = "ps", defaultValue = "2") int pageSize,
@RequestParam(value = "sortType", defaultValue = "auto") String sortType, ServletRequest request) {
Map<String, Object> searchParams = new HashMap<String, Object>();
searchParams = Servlets.getParametersStartingWith(request, "search_");
System.out.println(EncodeUtils.toUTF8((String)searchParams.get("LIKE_name")));
PageRequest pageRequest = QueryTool.buildPageRequest(pageNumber, pageSize, sortType);
searchParams.put(Operator.EQ + "_dr", "0");//逻辑删除中，字段dr=0表示这条数据没有删除
Specification<Comment> spec = QueryTool.buildSpecification(searchParams, Comment.class);
Page<Comment> page = commentDao.findAll(spec, pageRequest);
return JSON.toJSONString(page);
}

　　其中，Specification中的一些比较操作org.springside.modules.persistence.SearchFilter.Operator这个类中找到，如下：

public static enum Operator {
EQ, LIKE, GT, LT, GTE, LTE;
}

　　前台传递过来的参数名称中可以包含 Operator 中的一些操作， 比如参数名称是： search_LIKE_name (search表示要查询时比较， LIKE是比较的操作， name是表的字段名)。

5.java简单实现分页

public class MyPage{
private List<MyMessage> content;
private boolean first;
private boolean last;
private int number;
private int numberOfElements;
private int size;
private String totalElements;
private String sort;

public String getSort() {
return sort;
}

public void setSort(String sort) {
this.sort = sort;
}

public List<MyMessage> getContent() {
return content;
}

public void setContent(List<MyMessage> content) {
this.content = content;
}

public boolean isFirst() {
return first;
}

public void setFirst(boolean first) {
this.first = first;
}

public boolean isLast() {
return last;
}

public void setLast(boolean last) {
this.last = last;
}

public int getNumber() {
return number;
}

public void setNumber(int number) {
this.number = number;
}

public int getNumberOfElements() {
return numberOfElements;
}

public void setNumberOfElements(int numberOfElements) {
this.numberOfElements = numberOfElements;
}

public int getSize() {
return size;
}

public void setSize(int size) {
this.size = size;
}

public String getTotalElements() {
return totalElements;
}

public void setTotalElements(String totalElements) {
this.totalElements = totalElements;
}

public int getTotalPages() {
return totalPages;
}

public void setTotalPages(int totalPages) {
this.totalPages = totalPages;
}

private int totalPages;
}

View Code
　　实现思路：

1. 首先看一下后台的json数据的格式（其中message的值是spring Data JPA分页查询结果的json）

{"success":true,"message":{"content":[{"ccontent":"hjz 2016-38-11 15:38:21*****宋体|12|0-0-0| *****0$$$$$70#####","commentid":"8ae45d92549da2a801549ec092ce001f"},{"ccontent":"hjz 2016-38-11 15:38:10*****宋体|12|0-0-0|哇哇 *****2$$$$$55#####","commentid":"8ae45d92549da2a801549ec068c7001e"}],"first":true,"last":false,"number":0,"numberOfElements":2,"size":2,"sort":{},"totalElements":8,"totalPages":4}}

2. 将“message”对应的值转换成MyPage对象，因为MyPage中有一个List<MyMessage>,如果属性中含有复杂的类型，当其中属性有类似List , Map ,ArrayList、自定义的类型，如List<MyMessage> content, 普通的转换会报错：java.lang.ClassCastException: net.sf.ezmorph.bean.MorphDynaBean cannot be cast to XXX,在JSONObject.toBean的时候如果转换的类中有集合,可以先定义Map<String, Class> classMap = new HashMap<String, Class>();在classMap中put你要转换的类中的集合名 。本例中需要将“content”对应的值转换成 MyMessage对象。

//data为后台的json串
JSONObject result = JSONObject.fromObject(data);
if((Boolean) result.get("success")){//分页显示
JSONObject message = JSONObject.fromObject(result.get("message"));
Map<String, Class<?>> classMap = new HashMap<String, Class<?>>();
classMap.put("content", MyMessage.class);
MyPage myPage = (MyPage) JSONObject.toBean(message, MyPage.class, classMap);
this.updatePage(myPage);
}

3.然后通过分页的信息，简单的实现分页按钮，详情看MyPagePanel.java