Implementation of mybatis paging plug-in

In daily development, mybatis has become an important role in implementing the data persistence layer. The following is the implementation of a paging plug-in developed using mybatis. For more information about the plug-in concept of mybatis, see the mybatis website.

You can see from the official website that mybatis allows you to intercept the following methods.

1. Executor (Update, query, flushstatements, commit, rollback, gettransaction, close, isclosed)
2. Parameterhandler (getparameterobject, setparameters)
3. Resultsethandler (handleresultsets, handleoutputparameters)
4. Statementhandler (prepare, parameterize, batch, update, query)

Using the plug-in is very simple. You only need to implement the interceptor interface and specify the method signature you want to interceptor.

// ExamplePlugin.java@Intercepts({@Signature(  type= Executor.class,  method = "update",  args = {MappedStatement.class,Object.class})})public class ExamplePlugin implements Interceptor {  public Object intercept(Invocation invocation) throws Throwable {    return invocation.proceed();  }  public Object plugin(Object target) {    return Plugin.wrap(target, this);  }  public void setProperties(Properties properties) {  }}<!-- mybatis-config.xml --><plugins>  <plugin interceptor="org.mybatis.example.ExamplePlugin">    <property name="someProperty" value="100"/>  </plugin></plugins>

Explanation of tutorials on the official website:

1. User-Defined interceptor class needs to be implementedInterceptorInterface.
2. Specifies the method that the interceptor needs to intercept.ExamplePluginYesExecutor. ViewExecutorThe source code is as follows:
   Int Update (mappedstatement MS, object parameter) throws sqlexception;
3. Configuration File

The implementation of the paging plug-in is as follows:Executor
Java <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException;Method interception.

1. Define the interceptor class to implementInterceptorInterface to specify the method to intercept.

@ Intercepts ({@ signature (type = executor. class, method = "query", argS = {mappedstatement. class, object. class, rowbounds. class, resulthandler. class}) public class pageinterceptor implements interceptor {static int partition = 0; static int parameter_index = 1; static int rowbounds_index = 2; static int result_handler_index = 3; dialect; public object intercept (Invocation I Nvocation) throws throwable {processintercept (invocation. getargs (); Return invocation. proceed ();} void processintercept (final object [] queryargs) {mappedstatement MS = (mappedstatement) queryargs [mapped_statement_index]; object parameter = queryargs [parameter_index]; // obtain the page information rowbounds final rowbounds = (rowbounds) queryargs [rowbounds_index]; int pagecurrent = rowbounds. getoffset (); Int pagesize = rowbounds. getlimit (); // obtain the namespace and method string [] namespaceid = Ms. GETID (). Split ("\."); If (! Arrayutils. isempty (namespaceid) & namespaceid [namespaceid. Length-1]. startswith ("query") {If (dialect. supportslimit () & (pagecurrent! = Rowbounds. no_row_offset | pagesize! = Rowbounds. no_row_limit) {boundsql = Ms. getboundsql (parameter); string SQL = boundsql. getsql (). trim (); If (dialect. supportslimitoffset () {SQL = dialect. getpagesql (SQL, pagecurrent, pagesize); pagecurrent = rowbounds. no_row_offset;} else {SQL = dialect. getpagesql (SQL, 0, pagesize);} pagesize = rowbounds. no_row_limit; queryargs [rowbounds_index] = new rowbounds (pagecurrent, pagesize ); Boundsql newboundsql = new boundsql (Ms. getconfiguration (), SQL, boundsql. getparametermappings (), boundsql. getparameterobject (); mappedstatement newms = copyfrommappedstatement (MS, new boundsqlsqlsource (newboundsql); // you need to assign metaparameters values in the past .. metaobject countbsobject = systemmetaobject. forobject (newboundsql); metaobject boundsqlobject = systemmetaobject. forobject (boundsql); countbsobject. setvalu E ("metaparameters", boundsqlobject. getvalue ("metaparameters"); queryargs [mapped_statement_index] = newms ;}}/ ** @ see mapperbuilderassistant */private mappedstatement copyfrommappedstatement (mappedstatement MS, sqlsource newsqlsource) {Builder = new mappedstatement. builder (Ms. getconfiguration (), Ms. GETID (), newsqlsource, Ms. getsqlcommandtype (); builder. resource (Ms. getresource (); Bui Lder. fetchsize (Ms. getfetchsize (); builder. statementtype (Ms. getstatementtype (); builder. keygenerator (Ms. getkeygenerator (); builder. keyproperty (Ms. getkeyproperties () = NULL? Null: Ms. getkeyproperties () [0]); builder. timeout (Ms. gettimeout (); builder. parametermap (Ms. getparametermap (); builder. resultmaps (Ms. getresultmaps (); builder. resultsettype (Ms. getresultsettype (); builder. cache (Ms. getcache (); builder. flushcacherequired (Ms. isflushcacherequired (); builder. usecache (Ms. isusecache (); Return builder. build ();} public object plugin (object target) {return plugin. wrap (target, this);} public void setproperties (properties Properties) {try {string dialectclassvalue = properties. getproperty ("dialectclass"); If ("com. page. dialect. mysqldialect ". equals (dialectclassvalue) {dialect = (dialect) class. forname (mysqldialect. class. getcanonicalname ()). newinstance ();} else {dialect = (dialect) class. forname (oracledialect. class. getcanonicalname ()). newinstance () ;}} catch (exception e) {Throw new runtimeexception ("cannot create dialect instance by dialectclass:" + oracledialect. class. getcanonicalname (), e) ;}} public static class boundsqlsource implements sqlsource {boundsql; Public boundsqlsource (boundsql) {This. boundsql = boundsql;} public boundsql getboundsql (Object parameterobject) {return boundsql ;}}}

/*** Similar to dialect of hibernate, but only the paging part is simplified */public class dialect {/*** converts the SQL statement into a paging SQL statement </BR> * Splits the original SQL statement, assemble the required paging SQL. */Public String getpagesql (string SQL, int pagecurrent, int pagesize) {Throw new unsupportedoperationexception ("paged queries not supported");} public Boolean supportslimit () {return false ;} public Boolean supportslimitoffset () {return supportslimit ();}}

Public class mysqldialect extends dialect {Public String getpagesql (string SQL, int pagecurrent, int pagesize) {// original SQL string orgsql = SQL. trim (); // reset the current page pagecurrent = pagecurrent-1; // start data row int offset = pagecurrent * pagesize; // final SQL stringbuffer finalesql = new stringbuffer (); finalesql. append ("select * from ("); // append the original SQL statement finalesql. append (orgsql); // use limit to paging finalesql. append ("Limit" + String. valueof (offset) + "," + String. valueof (pagesize); finalesql. append (") as tabletotal"); Return finalesql. tostring ();} public Boolean supportslimit () {return true;} public Boolean supportslimitoffset () {return true ;}} public class oracledialect extends dialect {Public String getpagesql (string SQL, int pagecurrent, int pagesize) {// original SQL string orgsql = SQL. trim (); // reset the current page pagecurrent = pagecurrent-1; // final SQL stringbuffer finalesql = new stringbuffer (); // if the current page is greater than 0 finalesql. append ("select * from (select row _. *, rownum _ from ("); // append the original SQL statement finalesql. append (orgsql); // if the current page is greater than 0 if (pagecurrent> 0) {finalesql. append (") Row _) where rownum _ <=" + (pagecurrent * pagesize) + "+" + pagesize) + "and rownum _>" + String. valueof (pagecurrent * pagesize);} else {// if the current page <= 0 finalesql. append (") Row _) where rownum _ <=" + String. valueof (pagesize);} return finalesql. tostring () ;} public Boolean supportslimit () {return true;} public Boolean supportslimitoffset () {return true ;}} public class systemmetaobject {public static final objectfactory default_object_factory = new defaultobjectfactory (); public static final objectwrapperfactory metadata = new defaultobjectwrapperfactory (); public static final metaobject null_meta_object = metaobject. forobject (nullobject. class, default_object_factory, default_object_wrapper_factory); Private systemmetaobject () {// prevent instantiation of static class} Private Static class nullobject {} public static metaobject foject (Object object) {return metaobject. forobject (object, default_object_factory, default_object_wrapper_factory );}}

<configuration>    <properties>        <property name="dialect" value="oracle" />    </properties>    <settings>        <setting name="lazyLoadingEnabled" value="true" />        <setting name="jdbcTypeForNull" value="VARCHAR" />    </settings>    <plugins>        <plugin interceptor="com.page.interceptor.PageInterceptor">            <property name="dialectClass" value="com..page.dialect.OracleDialect" />        </plugin>    </plugins></configuration>

Implementation of mybatis paging plug-in