MyBatis-Plugins 的创建流程与执行顺序（源码）

一、插件的解析，所有插件都会被添加到 InterceptorChain 类中，用于后续处理

org.apache.ibatis.builder.xml.XMLConfigBuilder

private void pluginElement(XNode parent) throws Exception {
    if (parent != null) {
        for (XNode child : parent.getChildren()) {
            String interceptor = child.getStringAttribute("interceptor");
            Properties properties = child.getChildrenAsProperties();
            Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
            interceptorInstance.setProperties(properties);
            configuration.addInterceptor(interceptorInstance);
        }
    }
}

org.apache.ibatis.session.Configuration

public void addInterceptor(Interceptor interceptor) {
    interceptorChain.addInterceptor(interceptor);
}

二、四大对象的创建顺序，都会经过 interceptorChain.pluginAll() 进行处理

1.Executor，SQL语句执行器

org.apache.ibatis.session.Configuration

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    if (ExecutorType.BATCH == executorType) {
        executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
        executor = new ReuseExecutor(this, transaction);
    } else {
        executor = new SimpleExecutor(this, transaction);
    }
    if (cacheEnabled) {
        executor = new CachingExecutor(executor);
    }
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
}

2.ParameterHandler，参数处理器

org.apache.ibatis.executor.statement.BaseStatementHandler

protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    this.configuration = mappedStatement.getConfiguration();
    this.executor = executor;
    this.mappedStatement = mappedStatement;
    this.rowBounds = rowBounds;

    this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
    this.objectFactory = configuration.getObjectFactory();

    if (boundSql == null) { // issue #435, get the key before calculating the statement
        generateKeys(parameterObject);
        boundSql = mappedStatement.getBoundSql(parameterObject);
    }

    this.boundSql = boundSql;

    this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);
    this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);
}

org.apache.ibatis.session.Configuration

public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
    ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
    parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
    return parameterHandler;
}

3.ResultSetHandler，结果集处理器

org.apache.ibatis.executor.statement.BaseStatementHandler

protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    this.configuration = mappedStatement.getConfiguration();
    this.executor = executor;
    this.mappedStatement = mappedStatement;
    this.rowBounds = rowBounds;

    this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
    this.objectFactory = configuration.getObjectFactory();

    if (boundSql == null) { // issue #435, get the key before calculating the statement
        generateKeys(parameterObject);
        boundSql = mappedStatement.getBoundSql(parameterObject);
    }

    this.boundSql = boundSql;

    this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);
    this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);
}

org.apache.ibatis.session.Configuration

public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler, ResultHandler resultHandler, BoundSql boundSql) {
    ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);
    resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
    return resultSetHandler;
}

4.StatementHandler，SQL语句处理器

org.apache.ibatis.executor.SimpleExecutor

@Override
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
    Statement stmt = null;
    try {
        Configuration configuration = ms.getConfiguration();
        StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
        stmt = prepareStatement(handler, ms.getStatementLog());
        return handler.query(stmt, resultHandler);
    } finally {
        closeStatement(stmt);
    }
}

org.apache.ibatis.session.Configuration

public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
    statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
    return statementHandler;
}

三、多个不同类型插件的执行顺序

org.apache.ibatis.executor.SimpleExecutor

@Override
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
    Statement stmt = null;
    try {
        Configuration configuration = ms.getConfiguration();
        StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
        stmt = prepareStatement(handler, ms.getStatementLog());
        // 3.执行 SQL 语句，封装结果集，ResultSetHandler 拦截插件执行
        return handler.query(stmt, resultHandler);
    } finally {
        closeStatement(stmt);
    }
}

private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
    Statement stmt;
    Connection connection = getConnection(statementLog);
    // 1.准备语句，StatementHandler 拦截插件执行
    stmt = handler.prepare(connection, transaction.getTimeout());
    // 2.SQL 语句参数处理，ParameterHandler 拦截插件执行
    handler.parameterize(stmt);
    return stmt;
}

四、多个相同类型插件的执行顺序，以  StatementHandler 为例

1.创建顺序，按照配置顺序层层代理，最后配置的插件为最外层代理

配置了两个插件

<plugins>
    <plugin interceptor="com.plugins.ExamplePlugin"></plugin>
    <plugin interceptor="com.plugins.ExamplePlugin2"></plugin>
</plugins>

1.1.准备创建

1.2.最开始要执行的对象

1.3.开始创建

1.4.创建完毕

2.执行顺序，按照配置顺序倒序执行

2.1.第一次执行，ExamplePlugin2

2.2.第二次执行，ExamplePlugin

2.3.最终执行

3.示意图