1. Page
package com.sm.model;
import java.util.List;
public class Page<T> {
public static final int DEFAULT_PAGE_SIZE = 20;
protected int pageNo = 1; // 当前页, 默觉得第1页
protected int pageSize = DEFAULT_PAGE_SIZE; // 每页记录数
protected long totalRecord = -1; // 总记录数, 默觉得-1, 表示须要查询
protected int totalPage = -1; // 总页数, 默觉得-1, 表示须要计算
protected List<T> results; // 当前页记录List形式
public int getPageNo() {
return pageNo;
}
public void setPageNo(int pageNo) {
this.pageNo = pageNo;
}
public int getPageSize() {
return pageSize;
}
public void setPageSize(int pageSize) {
this.pageSize = pageSize;
computeTotalPage();
}
public long getTotalRecord() {
return totalRecord;
}
public int getTotalPage() {
return totalPage;
}
public void setTotalRecord(long totalRecord) {
this.totalRecord = totalRecord;
computeTotalPage();
}
protected void computeTotalPage() {
if (getPageSize() > 0 && getTotalRecord() > -1) {
this.totalPage = (int) (getTotalRecord() % getPageSize() == 0 ? getTotalRecord() / getPageSize() : getTotalRecord() / getPageSize() + 1);
}
}
public List<T> getResults() {
return results;
}
public void setResults(List<T> results) {
this.results = results;
}
@Override
public String toString() {
StringBuilder builder = new StringBuilder().append("Page [pageNo=").append(pageNo).append(", pageSize=").append(pageSize)
.append(", totalRecord=").append(totalRecord < 0 ? "null" : totalRecord).append(", totalPage=")
.append(totalPage < 0 ? "null" : totalPage).append(", results=").append(results == null ?
"null" : results).append("]");
return builder.toString();
}
}
2. 实现拦截器
package com.sm.model;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.executor.parameter.DefaultParameterHandler;
import org.apache.ibatis.executor.parameter.ParameterHandler;
import org.apache.ibatis.executor.statement.RoutingStatementHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ParameterMapping;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.plugin.Intercepts;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.plugin.Plugin;
import org.apache.ibatis.plugin.Signature;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
@Intercepts({ @Signature(method = "prepare", type = StatementHandler.class, args = { Connection.class }),
@Signature(method = "query", type = Executor.class, args = { MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class }) })
public class PageInterceptor implements Interceptor {
private static final Logger log = LoggerFactory.getLogger(PageInterceptor.class);
public static final String MYSQL = "mysql";
public static final String ORACLE = "oracle";
protected String databaseType;// 数据库类型。不同的数据库有不同的分页方法
protected ThreadLocal<Page> pageThreadLocal = new ThreadLocal<Page>();
public String getDatabaseType() {
return databaseType;
}
public void setDatabaseType(String databaseType) {
if (!databaseType.equalsIgnoreCase(MYSQL) && !databaseType.equalsIgnoreCase(ORACLE)) {
throw new PageNotSupportException("Page not support for the type of database, database type [" + databaseType + "]");
}
this.databaseType = databaseType;
}
@Override
public Object plugin(Object target) {
return Plugin.wrap(target, this);
}
@Override
public void setProperties(Properties properties) {
String databaseType = properties.getProperty("databaseType");
if (databaseType != null) {
setDatabaseType(databaseType);
}
}
@Override
@SuppressWarnings({ "unchecked", "rawtypes" })
public Object intercept(Invocation invocation) throws Throwable {
if (invocation.getTarget() instanceof StatementHandler) {// 控制SQL和查询总数的地方
Page page = pageThreadLocal.get();
if (page == null) { //不是分页查询
return invocation.proceed();
}
RoutingStatementHandler handler = (RoutingStatementHandler) invocation.getTarget();
StatementHandler delegate = (StatementHandler) ReflectUtil.getFieldValue(handler, "delegate");
BoundSql boundSql = delegate.getBoundSql();
Connection connection = (Connection) invocation.getArgs()[0];
prepareAndCheckDatabaseType(connection); // 准备数据库类型
if (page.getTotalPage() > -1) {
if (log.isTraceEnabled()) {
log.trace("已经设置了总页数, 不须要再查询总数.");
}
} else {
Object parameterObj = boundSql.getParameterObject();
MappedStatement mappedStatement = (MappedStatement) ReflectUtil.getFieldValue(delegate, "mappedStatement");
queryTotalRecord(page, parameterObj, mappedStatement, connection);
}
String sql = boundSql.getSql();
String pageSql = buildPageSql(page, sql);
if (log.isDebugEnabled()) {
log.debug("分页时, 生成分页pageSql: " + pageSql);
}
ReflectUtil.setFieldValue(boundSql, "sql", pageSql);
return invocation.proceed();
} else { // 查询结果的地方
// 获取是否有分页Page对象
Page<?> page = findPageObject(invocation.getArgs()[1]);
if (page == null) {
if (log.isTraceEnabled()) {
log.trace("没有Page对象作为參数, 不是分页查询.");
}
return invocation.proceed();
} else {
if (log.isTraceEnabled()) {
log.trace("检測到分页Page对象, 使用分页查询.");
}
}
//设置真正的parameterObj
invocation.getArgs()[1] = extractRealParameterObject(invocation.getArgs()[1]);
pageThreadLocal.set(page);
try {
Object resultObj = invocation.proceed(); // Executor.query(..)
if (resultObj instanceof List) {
/* @SuppressWarnings({ "unchecked", "rawtypes" }) */
page.setResults((List) resultObj);
}
return resultObj;
} finally {
pageThreadLocal.remove();
}
}
}
protected Page<?> findPageObject(Object parameterObj) {
if (parameterObj instanceof Page<?>) {
return (Page<?>) parameterObj;
} else if (parameterObj instanceof Map) {
for (Object val : ((Map<?, ?
>) parameterObj).values()) {
if (val instanceof Page<?>) {
return (Page<?
>) val;
}
}
}
return null;
}
/**
* <pre>
* 把真正的參数对象解析出来
* Spring会自己主动封装对个參数对象为Map<String, Object>对象
* 对于通过@Param指定key值參数我们不做处理，由于XML文件须要该KEY值
* 而对于没有@Param指定时，Spring会使用0,1作为主键
* 对于没有@Param指定名称的參数,一般XML文件会直接对真正的參数对象解析。
* 此时解析出真正的參数作为根对象
* </pre>
* @author jundong.xu_C
* @param parameterObj
* @return
*/
protected Object extractRealParameterObject(Object parameterObj) {
if (parameterObj instanceof Map<?, ?>) {
Map<?, ?
> parameterMap = (Map<?, ?>) parameterObj;
if (parameterMap.size() == 2) {
boolean springMapWithNoParamName = true;
for (Object key : parameterMap.keySet()) {
if (!(key instanceof String)) {
springMapWithNoParamName = false;
break;
}
String keyStr = (String) key;
if (!"0".equals(keyStr) && !"1".equals(keyStr)) {
springMapWithNoParamName = false;
break;
}
}
if (springMapWithNoParamName) {
for (Object value : parameterMap.values()) {
if (!(value instanceof Page<?
>)) {
return value;
}
}
}
}
}
return parameterObj;
}
protected void prepareAndCheckDatabaseType(Connection connection) throws SQLException {
if (databaseType == null) {
String productName = connection.getMetaData().getDatabaseProductName();
if (log.isTraceEnabled()) {
log.trace("Database productName: " + productName);
}
productName = productName.toLowerCase();
if (productName.indexOf(MYSQL) != -1) {
databaseType = MYSQL;
} else if (productName.indexOf(ORACLE) != -1) {
databaseType = ORACLE;
} else {
throw new PageNotSupportException("Page not support for the type of database, database product name [" + productName + "]");
}
if (log.isInfoEnabled()) {
log.info("自己主动检測到的数据库类型为: " + databaseType);
}
}
}
/**
* <pre>
* 生成分页SQL
* </pre>
*
* @author jundong.xu_C
* @param page
* @param sql
* @return
*/
protected String buildPageSql(Page<?> page, String sql) {
if (MYSQL.equalsIgnoreCase(databaseType)) {
return buildMysqlPageSql(page, sql);
} else if (ORACLE.equalsIgnoreCase(databaseType)) {
return buildOraclePageSql(page, sql);
}
return sql;
}
/**
* <pre>
* 生成Mysql分页查询SQL
* </pre>
*
* @author jundong.xu_C
* @param page
* @param sql
* @return
*/
protected String buildMysqlPageSql(Page<?> page, String sql) {
// 计算第一条记录的位置，Mysql中记录的位置是从0開始的。
int offset = (page.getPageNo() - 1) * page.getPageSize();
return new StringBuilder(sql).append(" limit ").append(offset).append(",").append(page.getPageSize()).toString();
}
/**
* <pre>
* 生成Oracle分页查询SQL
* </pre>
*
* @author jundong.xu_C
* @param page
* @param sql
* @return
*/
protected String buildOraclePageSql(Page<?> page, String sql) {
// 计算第一条记录的位置。Oracle分页是通过rownum进行的。而rownum是从1開始的
int offset = (page.getPageNo() - 1) * page.getPageSize() + 1;
StringBuilder sb = new StringBuilder(sql);
sb.insert(0, "select u.*, rownum r from (").append(") u where rownum < ").append(offset + page.getPageSize());
sb.insert(0, "select * from (").append(") where r >= ").append(offset);
return sb.toString();
}
/**
* <pre>
* 查询总数
* </pre>
*
* @author jundong.xu_C
* @param page
* @param parameterObject
* @param mappedStatement
* @param connection
* @throws SQLException
*/
protected void queryTotalRecord(Page<?> page, Object parameterObject, MappedStatement mappedStatement, Connection connection) throws SQLException {
BoundSql boundSql = mappedStatement.getBoundSql(page);
String sql = boundSql.getSql();
String countSql = this.buildCountSql(sql);
if (log.isDebugEnabled()) {
log.debug("分页时, 生成countSql: " + countSql);
}
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
BoundSql countBoundSql = new BoundSql(mappedStatement.getConfiguration(), countSql, parameterMappings, parameterObject);
ParameterHandler parameterHandler = new DefaultParameterHandler(mappedStatement, parameterObject, countBoundSql);
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
pstmt = connection.prepareStatement(countSql);
parameterHandler.setParameters(pstmt);
rs = pstmt.executeQuery();
if (rs.next()) {
long totalRecord = rs.getLong(1);
page.setTotalRecord(totalRecord);
}
} finally {
if (rs != null)
try {
rs.close();
} catch (Exception e) {
if (log.isWarnEnabled()) {
log.warn("关闭ResultSet时异常.", e);
}
}
if (pstmt != null)
try {
pstmt.close();
} catch (Exception e) {
if (log.isWarnEnabled()) {
log.warn("关闭PreparedStatement时异常.", e);
}
}
}
}
/**
* 依据原Sql语句获取相应的查询总记录数的Sql语句
*
* @param sql
* @return
*/
protected String buildCountSql(String sql) {
int index = sql.indexOf("from");
return "select count(*) " + sql.substring(index);
}
/**
* 利用反射进行操作的一个工具类
*
*/
private static class ReflectUtil {
/**
* 利用反射获取指定对象的指定属性
*
* @param obj 目标对象
* @param fieldName 目标属性
* @return 目标属性的值
*/
public static Object getFieldValue(Object obj, String fieldName) {
Object result = null;
Field field = ReflectUtil.getField(obj, fieldName);
if (field != null) {
field.setAccessible(true);
try {
result = field.get(obj);
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return result;
}
/**
* 利用反射获取指定对象里面的指定属性
*
* @param obj 目标对象
* @param fieldName 目标属性
* @return 目标字段
*/
private static Field getField(Object obj, String fieldName) {
Field field = null;
for (Class<?> clazz = obj.getClass(); clazz != Object.class; clazz = clazz.getSuperclass()) {
try {
field = clazz.getDeclaredField(fieldName);
break;
} catch (NoSuchFieldException e) {
// 杩欓噷涓嶇敤鍋氬�鐞嗭紝瀛愮被娌℃湁璇ュ瓧娈靛彲鑳藉�搴旂殑鐖剁被鏈夛紝閮芥病鏈夊氨杩斿洖null銆�
}
}
return field;
}
/**
* 利用反射设置指定对象的指定属性为指定的值
*
* @param obj 目标对象
* @param fieldName 目标属性
* @param fieldValue 目标值
*/
public static void setFieldValue(Object obj, String fieldName, String fieldValue) {
Field field = ReflectUtil.getField(obj, fieldName);
if (field != null) {
try {
field.setAccessible(true);
field.set(obj, fieldValue);
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
public static class PageNotSupportException extends RuntimeException {
public PageNotSupportException() {
super();
}
public PageNotSupportException(String message, Throwable cause) {
super(message, cause);
}
public PageNotSupportException(String message) {
super(message);
}
public PageNotSupportException(Throwable cause) {
super(cause);
}
}
}
3. spring配置文件（mybatis已和spring整合）
<!-- 配置mybatis的sqlSessionFactory -->
<bean id="sqlSessionFactoryBean" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource"></property>
<!-- 配置了typeAliasesPackage之后，在映射文件里，这个包下的实体类能够不写全名 -->
<property name="typeAliasesPackage" value="com.sm.model"></property>
<!-- 配置映射映射文件的位置 -->
<property name="mapperLocations" value="classpath:resources/mapper/*.xml"></property>
<property name="plugins">
<!-- 分页拦截器 -->
<bean class="com.sm.model.PageInterceptor"></bean>
</property>
</bean>4. mapper.xml
<select id="getUsers" resultType="User" parameterType="Map">
select * from user where username=#{user.username}
</select>6. DAO
List<User> getUsers(Map map);7. 測试
Page page = new Page();
//配置分页參数
page.setPageNo(1);
page.setPageSize(3);
//条件查询，传參
User user = new User();
user.setUsername("2");
Map map = new HashMap<>();
map.put("user", user);
map.put("page", page);
List<User> list = userDAO.getUsers(map);
System.out.println(list);
System.out.println(page);
8. 总结
上面的分页拦截器，拷下来直接用就好了。假设想了解实现原理。能够看慕课网的视频通过自己主动回复机器人学Mybatis—加强版