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mysql分页查询的时候有深度翻页的问题，如果我们需要查询全部数据的时候，不可能一次查询全部，这个时候就可以使用游标，游标的原理其实就是顺序查询，只是每次查询到一些数据后会先返回给我们，然后继续往后查询。这样解决了等待问题，也解决了内存爆炸问题。下面通过mybatis介绍一下游标的使用。

使用方式

@Componentpublic class PersonResultHandler implements ResultHandler
   
     {    @Override    public void handleResult(ResultContext
     resultContext) {        System.out.println(resultContext.isStopped());        System.out.println(resultContext.getResultObject());    }}@Mapperpublic interface PersonMapper {    Person getById(@Param("id") Long id);    int create(Person person);    void findAll(ResultHandler
    
      resultHandler);}    
             select        `id` as `id`,        `name` as `name`,        `desc` as `desc`,        `nationality_id` as `nationalityId`        from person    
    
   

思路

mybatis提供了两个接口，可以通过游标查询。

void select(String var1, Object var2, ResultHandler var3);    void select(String var1, ResultHandler var2);

根据this.method.returnsVoid() && this.method.hasResultHandler()可以知道，如果接口返回值为void并且包含resultHandler接口，则可以使用游标查询。

public Object execute(SqlSession sqlSession, Object[] args) {        Object param;        Object result;        switch(this.command.getType()) {        case INSERT:            param = this.method.convertArgsToSqlCommandParam(args);            result = this.rowCountResult(sqlSession.insert(this.command.getName(), param));            break;        case UPDATE:            param = this.method.convertArgsToSqlCommandParam(args);            result = this.rowCountResult(sqlSession.update(this.command.getName(), param));            break;        case DELETE:            param = this.method.convertArgsToSqlCommandParam(args);            result = this.rowCountResult(sqlSession.delete(this.command.getName(), param));            break;        case SELECT:            if (this.method.returnsVoid() && this.method.hasResultHandler()) {                this.executeWithResultHandler(sqlSession, args);                result = null;            } else if (this.method.returnsMany()) {                result = this.executeForMany(sqlSession, args);            } else if (this.method.returnsMap()) {                result = this.executeForMap(sqlSession, args);            } else if (this.method.returnsCursor()) {                result = this.executeForCursor(sqlSession, args);            } else {                param = this.method.convertArgsToSqlCommandParam(args);                result = sqlSession.selectOne(this.command.getName(), param);            }            break;        case FLUSH:            result = sqlSession.flushStatements();            break;        default:            throw new BindingException("Unknown execution method for: " + this.command.getName());        }        if (result == null && this.method.getReturnType().isPrimitive() && !this.method.returnsVoid()) {            throw new BindingException("Mapper method '" + this.command.getName() + " attempted to return null from a method with a primitive return type (" + this.method.getReturnType() + ").");        } else {            return result;        }    }

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