Mybatis插件Plugin解析
一、Mybatis插件Plugin解析
二、Mybatis插件模拟代码
一、Mybatis插件Plugin解析
Mybatis插件能对4大对象进行代理拦截 。 Executor、StatementHandler、ParameterHandler、ResultSetHandler
相关代码都在Configuration中
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; } |
public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) { ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql); parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler); return parameterHandler; } |
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; } |
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; } |
下面看下具体操作
public class InterceptorChain {
// 在解析mybatis-config.xml的时候，会将拦截器存入interceptors
private final List<Interceptor> interceptors = new ArrayList<>();
public Object pluginAll(Object target) {
for (Interceptor interceptor : interceptors) {
// 如果有多个拦截器 ，第一个拦截器生成target的代理对象targetProxy0 ,
// 第二个拦截器生成targetProxy0的代理对象targetProxy1 ,
// 第三个拦截器生成targetProxy1的代理对象targetProxy2 , 依此类推……
// 所以代理是可以被代理的。
// 调用时执行顺序是先调用最外层的，依次向内，最终才会调用目标方法
target = interceptor.plugin(target);
}
return target;
}
// 在解析mybatis-config.xml的时候，会调用此方法
public void addInterceptor(Interceptor interceptor) {
interceptors.add(interceptor);
}
public List<Interceptor> getInterceptors() {
return Collections.unmodifiableList(interceptors);
}
}import org.apache.ibatis.builder.StaticSqlSource;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlSource;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.util.Properties;
@Intercepts({@Signature(type = StatementHandler.class,method = "prepare",
args = {Connection.class, Integer.class})
})
public class MyPageInterceptor implements Interceptor {
@Override
public Object intercept(Invocation invocation) throws Throwable {
//在这里处理自己的业务逻辑
// ………………
// 执行被拦截方法
return invocation.proceed();
}
@Override
public Object plugin(Object target) {
// 关键代码
return Plugin.wrap(target, this);
}
@Override
public void setProperties(Properties properties) {
}
}package org.apache.ibatis.plugin;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import org.apache.ibatis.reflection.ExceptionUtil;
public class Plugin implements InvocationHandler {
private final Object target;
private final Interceptor interceptor;
private final Map<Class<?>, Set<Method>> signatureMap;
private Plugin(Object target, Interceptor interceptor, Map<Class<?>, Set<Method>> signatureMap) {
this.target = target;
this.interceptor = interceptor;
this.signatureMap = signatureMap;
}
public static Object wrap(Object target, Interceptor interceptor) {
// 获取拦截器的注解上 需要被拦截的类和被拦截方法
Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
Class<?> type = target.getClass();
Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
// 符合拦截条件的，生成代理对象
if (interfaces.length > 0) {
return Proxy.newProxyInstance(
type.getClassLoader(),
interfaces,
new Plugin(target, interceptor, signatureMap));
}
return target;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
// 判断当前method是否需要被拦截
Set<Method> methods = signatureMap.get(method.getDeclaringClass());
if (methods != null && methods.contains(method)) {
return interceptor.intercept(new Invocation(target, method, args));
}
return method.invoke(target, args);
} catch (Exception e) {
throw ExceptionUtil.unwrapThrowable(e);
}
}
private static Map<Class<?>, Set<Method>> getSignatureMap(Interceptor interceptor) {
Intercepts interceptsAnnotation = interceptor.getClass().getAnnotation(Intercepts.class);
// issue #251
if (interceptsAnnotation == null) {
throw new PluginException("No @Intercepts annotation was found in interceptor " + interceptor.getClass().getName());
}
Signature[] sigs = interceptsAnnotation.value();
Map<Class<?>, Set<Method>> signatureMap = new HashMap<>();
for (Signature sig : sigs) {
Set<Method> methods = signatureMap.computeIfAbsent(sig.type(), k -> new HashSet<>());
try {
Method method = sig.type().getMethod(sig.method(), sig.args());
methods.add(method);
} catch (NoSuchMethodException e) {
throw new PluginException("Could not find method on " + sig.type() + " named " + sig.method() + ". Cause: " + e, e);
}
}
return signatureMap;
}
private static Class<?>[] getAllInterfaces(Class<?> type, Map<Class<?>, Set<Method>> signatureMap) {
Set<Class<?>> interfaces = new HashSet<>();
while (type != null) {
for (Class<?> c : type.getInterfaces()) {
if (signatureMap.containsKey(c)) {
interfaces.add(c);
}
}
type = type.getSuperclass();
}
return interfaces.toArray(new Class<?>[0]);
}
}如果配置了相应的拦截器，在Executor、StatementHandler、ParameterHandler、ResultSetHandler调用其方法时，会先执行Plugin的invoke方法(动态代理设置的回调类为Plugin) , 确定该方法被拦截，然后执行Interceptor中的intercept方法 , 所有代理方法执行完成后，就执行目标方法。
二、Mybatis插件模拟代码
package com.example.demo.proxy;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;
public class PluginDemo {
public static void main(String[] args) {
UserService userService = new UserServiceImpl();
userService = (UserService) getProxy(userService);
String doBusiness = userService.doBusiness(1001);
System.out.println("doBusiness : " + doBusiness);
}
public static Object getProxy(Object obj) {
List<Interceptor> list = new ArrayList<Interceptor>();
// 3层代理
list.add(new MyInterceptor1());
list.add(new MyInterceptor2());
list.add(new MyInterceptor3());
for (Interceptor interceptor : list) {
obj = newProxy(obj, interceptor);
}
return obj;
}
public static Object newProxy(Object obj, Interceptor interceptor) {
return Proxy.newProxyInstance(PluginDemo.class.getClassLoader(), obj.getClass().getInterfaces(),
new MyInvocation(obj, interceptor));
}
}package com.example.demo.proxy;
interface UserService {
String doBusiness(int id);
String getMsg();
void setMsg(String msg);
}package com.example.demo.proxy;
public class UserServiceImpl implements UserService {
private String msg;
public UserServiceImpl() {
this.msg = "UserServiceImpl msg " ;
}
@Override
public String doBusiness(int id) {
return "name : " + id;
}
@Override
public String getMsg() {
return msg;
}
public void setMsg(String msg) {
this.msg = msg;
}
}package com.example.demo.proxy;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
/**
* 动态代理的回调类
*/
public class MyInvocation implements InvocationHandler {
private Interceptor interceptor;
private Object obj;
public MyInvocation(Object obj, Interceptor interceptor) {
this.interceptor = interceptor;
this.obj = obj;
}
public MyInvocation() {
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName() ;
/**
* 拦截指定方法，不然会拦截所有的方法，执行就会很乱
*/
if (interceptor != null && "doBusiness".equals(methodName)) {
return interceptor.intercept(obj, method, args);
} else {
return method.invoke(obj, args);
}
}
}package com.example.demo.proxy;
import java.lang.reflect.Method;
public interface Interceptor {
public Object intercept(Object obj, Method method, Object[] args);
}package com.example.demo.proxy;
import java.lang.reflect.Method;
public class MyInterceptor1 implements Interceptor {
@Override
public Object intercept(Object obj, Method method, Object[] args) {
UserService u = (UserService) obj;
System.out.println("MyInterceptor1 " + u.getMsg());
u.setMsg("MyInterceptor1 msg");
try {
return method.invoke(obj, args);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}package com.example.demo.proxy;
import java.lang.reflect.Method;
public class MyInterceptor2 implements Interceptor {
@Override
public Object intercept(Object obj, Method method, Object[] args) {
UserService u = (UserService) obj;
System.out.println("MyInterceptor2 " + u.getMsg());
u.setMsg("MyInterceptor2 msg");
try {
return method.invoke(obj, args);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}package com.example.demo.proxy;
import java.lang.reflect.Method;
public class MyInterceptor3 implements Interceptor {
@Override
public Object intercept(Object obj, Method method, Object[] args) {
UserService u = (UserService) obj;
System.out.println("MyInterceptor3 " + u.getMsg());
u.setMsg("MyInterceptor3 msg");
try {
return method.invoke(obj, args);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}执行主类PluginDemo， 打印：
MyInterceptor3 UserServiceImpl msg MyInterceptor2 MyInterceptor3 msg MyInterceptor1 MyInterceptor2 msg doBusiness : name : 1001 |
