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As a good framework, which in addition to solve most of the process, we also need the ability to provide user can customize. MyBatisThere cache, there are plug-in interface. We can customize the way for plug-ins to MyBatisextend the use.
With a simple mysql pagination plug-in, for example, the use of plug-in includes the following steps:
1 of paging parameters passed
Paging parameter is the offset and limit. It can be used RowBoundsto transfer, but this need to make changes to the original method. Accordingly, by the present example ThreadLocalfor analgesia delivery.
/**
* @author homejim
*/
public class PageUtil {
private static final ThreadLocal<Page> LOCAL_PAGE = new ThreadLocal<Page>();
public static void setPagingParam(int offset, int limit) {
Page page = new Page(offset, limit);
LOCAL_PAGE.set(page);
}
public static void removePagingParam() {
LOCAL_PAGE.remove();
}
public static Page getPaingParam() {
return LOCAL_PAGE.get();
}
}In actual use, a user just have to call the prior PageUtil#setPagingParammethod of paging parameters to be passed. Without subsequent treatment.
2 implement Interceptor
2.1 Interceptor Interface Description
Take a look at the Interceptor interface.
/**
* 拦截器接口
*
* @author Clinton Begin
*/
public interface Interceptor {
/**
* 执行拦截逻辑的方法
*
* @param invocation 调用信息
* @return 调用结果
* @throws Throwable 异常
*/
Object intercept(Invocation invocation) throws Throwable;
/**
* 代理类
*
* @param target
* @return
*/
Object plugin(Object target);
/**
* 根据配置来初始化 Interceptor 方法
* @param properties
*/
void setProperties(Properties properties);
}Therefore, in actual use. We want to cover these methods.
Notes 2.1 Description
In the mybatismethod, it may comprise blocking
- Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
- ParameterHandler (getParameterObject, setParameters)
- ResultSetHandler (handleResultSets, handleOutputParameters)
- StatementHandler (prepare, parameterize, batch, update, query)
But the interface is only one Interceptor, therefore, require the use of annotations @Interceptsand @Signatureto specify the intercept method.
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface Intercepts {
Signature[] value();
}InterceptsAnnotations are Signaturenotes of an array.
/**
* 方法签名信息
*
* @author Clinton Begin
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({})
public @interface Signature {
/**
* 需要拦截的类型
*
* @return
*/
Class<?> type();
/**
* 需要拦截的方法
* @return
*/
String method();
/**
* 被拦截方法的参数列表
*
* @return
*/
Class<?>[] args();
}2.3 implement paging interfaces PageInterceptor
/**
* 分页插件
*
* @author homejim
*/
@Intercepts({
@Signature(
type = Executor.class,
method = "query",
args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}
)
})
@Slf4j
public class PageInterceptor implements Interceptor {
private static int MAPPEDSTATEMENT_INDEX = 0;
private static int PARAMETER_INDEX = 1;
private static int ROWBOUNDS_INDEX = 2;
@Override
public Object intercept(Invocation invocation) throws Throwable {
// 从 Invocation 中获取参数
final Object[] queryArgs = invocation.getArgs();
final MappedStatement ms = (MappedStatement) queryArgs[MAPPEDSTATEMENT_INDEX];
final Object parameter = queryArgs[PARAMETER_INDEX];
// 获取分页参数
Page paingParam = PageUtil.getPaingParam();
if (paingParam != null) {
// 构造新的 sql, select xxx from xxx where yyy limit offset,limit
final BoundSql boundSql = ms.getBoundSql(parameter);
String pagingSql = getPagingSql(boundSql.getSql(), paingParam.getOffset(), paingParam.getLimit());
// 设置新的 MappedStatement
BoundSql newBoundSql = new BoundSql(ms.getConfiguration(), pagingSql,
boundSql.getParameterMappings(), boundSql.getParameterObject());
MappedStatement mappedStatement = newMappedStatement(ms, newBoundSql);
queryArgs[MAPPEDSTATEMENT_INDEX] = mappedStatement;
// 重置 RowBound
queryArgs[ROWBOUNDS_INDEX] = new RowBounds(RowBounds.NO_ROW_OFFSET, RowBounds.NO_ROW_LIMIT);
}
Object result = invocation.proceed();
PageUtil.removePagingParam();
return result;
}
@Override
public Object plugin(Object o) {
return Plugin.wrap(o, this);
}
@Override
public void setProperties(Properties properties) {
}
/**
* 创建 MappedStatement
* @param ms
* @param newBoundSql
* @return
*/
private MappedStatement newMappedStatement(MappedStatement ms, BoundSql newBoundSql) {
MappedStatement.Builder builder = new MappedStatement.Builder(ms.getConfiguration(), ms.getId(),
new BoundSqlSqlSource(newBoundSql), ms.getSqlCommandType());
builder.keyColumn(delimitedArrayToString(ms.getKeyColumns()));
builder.keyGenerator(ms.getKeyGenerator());
builder.keyProperty(delimitedArrayToString(ms.getKeyProperties()));
builder.lang(ms.getLang());
builder.resource(ms.getResource());
builder.parameterMap(ms.getParameterMap());
builder.resultMaps(ms.getResultMaps());
builder.resultOrdered(ms.isResultOrdered());
builder.resultSets(delimitedArrayToString(ms.getResultSets()));
builder.resultSetType(ms.getResultSetType());
builder.timeout(ms.getTimeout());
builder.statementType(ms.getStatementType());
builder.useCache(ms.isUseCache());
builder.cache(ms.getCache());
builder.databaseId(ms.getDatabaseId());
builder.fetchSize(ms.getFetchSize());
builder.flushCacheRequired(ms.isFlushCacheRequired());
return builder.build();
}
public String getPagingSql(String sql, int offset, int limit) {
StringBuilder result = new StringBuilder(sql.length() + 100);
result.append(sql).append(" limit ");
if (offset > 0) {
result.append(offset).append(",").append(limit);
}else{
result.append(limit);
}
return result.toString();
}
public String delimitedArrayToString(String[] array) {
if (array == null || array.length == 0) {
return "";
}
Joiner joiner = Joiner.on(",");
return joiner.join(array);
}
}
According to the previous notes explain, we want to block a Executorclass in the following ways
<E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException;After the interception
- Get paging parameters
- According to rewrite the sql parameter
- Generate a new
MappedStatementobject to the proxy method - After the execution is complete removal of paging parameters
3. Change the configuration
After the above steps, mybatis we still do not know what are the interface and which interfaces need. Accordingly, the rearrangement will be described.
In the mybatis-config.xmlfile, add the following configuration
<plugins>
<plugin interceptor="com.homejim.mybatis.plugin.PageInterceptor">
</plugin>
</plugins>4 Test
@Test
public void testSelectList() {
SqlSession sqlSession = null;
try {
sqlSession = sqlSessionFactory.openSession();
PageUtil.setPagingParam(1, 2);
List<Student> students = sqlSession.selectList("selectAll");
for (int i = 0; i < students.size(); i++) {
System.out.println(students.get(i));
}
List<Student> students2 = sqlSession.selectList("selectAll");
for (int i = 0; i < students2.size(); i++) {
System.out.println(students2.get(i));
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (sqlSession != null) {
sqlSession.close();
}
}
}Among them, the first query to use paging, the second is not used. The results following
the first query to use paging, therefore limit, the second query is no, so check out all the results.
More use, visit my GitHub project