# Spring RMI
- Author: [HuiFer](https://github.com/huifer)
- 源码阅读仓库: [SourceHot-Spring](https://github.com/SourceHot/spring-framework-read)
- Spring 远程服务调用
## DEMO
### 服务提供方
- 服务提供方需要准备**接口**、**接口实现泪**
- 接口
```java
public interface IDemoRmiService {
int add(int a, int b);
}
```
- 接口实现
```java
public class IDemoRmiServiceImpl implements IDemoRmiService {
@Override
public int add(int a, int b) {
return a + b;
}
}
```
- xml 配置文件
```xml
```
- 运行
```java
public class RMIServerSourceCode {
public static void main(String[] args) throws Exception {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("rmi/RMISourceCode.xml");
}
}
```
### 服务调用方
- xml 配置
```java
```
**注意:rmi 使用小写**
大写报错信息:
```text
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'rmiClient' defined in class path resource [rmi/RMIClientSourceCode.xml]: Invocation of init method failed; nested exception is org.springframework.remoting.RemoteLookupFailureException: Service URL [RMI://localhost:9999/springRmi] is invalid; nested exception is java.net.MalformedURLException: invalid URL scheme: RMI://localhost:9999/springRmi
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1795)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:559)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:478)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:309)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:272)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:176)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:877)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:953)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:579)
at org.springframework.context.support.ClassPathXmlApplicationContext.(ClassPathXmlApplicationContext.java:163)
at org.springframework.context.support.ClassPathXmlApplicationContext.(ClassPathXmlApplicationContext.java:90)
at com.huifer.source.spring.rmi.RMIClientSourceCode.main(RMIClientSourceCode.java:7)
Caused by: org.springframework.remoting.RemoteLookupFailureException: Service URL [RMI://localhost:9999/springRmi] is invalid; nested exception is java.net.MalformedURLException: invalid URL scheme: RMI://localhost:9999/springRmi
at org.springframework.remoting.rmi.RmiClientInterceptor.lookupStub(RmiClientInterceptor.java:209)
at org.springframework.remoting.rmi.RmiClientInterceptor.prepare(RmiClientInterceptor.java:147)
at org.springframework.remoting.rmi.RmiClientInterceptor.afterPropertiesSet(RmiClientInterceptor.java:134)
at org.springframework.remoting.rmi.RmiProxyFactoryBean.afterPropertiesSet(RmiProxyFactoryBean.java:68)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1868)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1791)
... 12 more
Caused by: java.net.MalformedURLException: invalid URL scheme: RMI://localhost:9999/springRmi
at java.rmi.Naming.intParseURL(Naming.java:290)
at java.rmi.Naming.parseURL(Naming.java:237)
at java.rmi.Naming.lookup(Naming.java:96)
at org.springframework.remoting.rmi.RmiClientInterceptor.lookupStub(RmiClientInterceptor.java:201)
... 17 more
```
- 运行
```java
public class RMIClientSourceCode {
public static void main(String[] args) {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("rmi/RMIClientSourceCode.xml");
IDemoRmiService rmiClient = context.getBean("rmiClient", IDemoRmiService.class);
int add = rmiClient.add(1, 2);
System.out.println(add);
}
}
```
---
## 服务端初始化
- `org.springframework.remoting.rmi.RmiServiceExporter`,该类定义了 spring 的远程服务信息
### RmiServiceExporter
- 基础属性如下
```java
public class RmiServiceExporter extends RmiBasedExporter implements InitializingBean, DisposableBean {
/**
* 服务名称,rmi的服务名,在Spring中使用ref指向impl实现类
*/
private String serviceName;
/**
*
*/
private int servicePort = 0; // anonymous port
private RMIClientSocketFactory clientSocketFactory;
private RMIServerSocketFactory serverSocketFactory;
private Registry registry;
/**
* 注册的IP地址
*/
private String registryHost;
/**
* 注册的端口
*/
private int registryPort = Registry.REGISTRY_PORT;
/**
* 进行远程对象调用的Socket工厂
*/
private RMIClientSocketFactory clientSocketFactory;
/**
* 接收远程调用服务端的Socket工厂
*/
private RMIServerSocketFactory serverSocketFactory;
/**
* true: 该参数在获取{@link Registry}时测试是否建立连接,如果建立连接则直接使用,否则创建新连接
* 是否总是创建{@link Registry}
*/
private boolean alwaysCreateRegistry = false;
/**
* 设置替换RMI注册表中的绑定关系
*/
private boolean replaceExistingBinding = true;
private Remote exportedObject;
/**
* 创建{@link Registry}
*/
private boolean createdRegistry = false;
}
```
- 属性设置不说了,看接口实现了那些
1. InitializingBean: 初始化 bean 调用`afterPropertiesSet`方法
2. DisposableBean: 摧毁 bean 调用`destroy`方法
```java
@Override
public void afterPropertiesSet() throws RemoteException {
prepare();
}
public void prepare() throws RemoteException {
// 校验service
checkService();
// 服务名称校验
if (this.serviceName == null) {
throw new IllegalArgumentException("Property 'serviceName' is required");
}
// Check socket factories for exported object.
if (this.clientSocketFactory instanceof RMIServerSocketFactory) {
this.serverSocketFactory = (RMIServerSocketFactory) this.clientSocketFactory;
}
if ((this.clientSocketFactory != null && this.serverSocketFactory == null) ||
(this.clientSocketFactory == null && this.serverSocketFactory != null)) {
throw new IllegalArgumentException(
"Both RMIClientSocketFactory and RMIServerSocketFactory or none required");
}
// Check socket factories for RMI registry.
if (this.registryClientSocketFactory instanceof RMIServerSocketFactory) {
this.registryServerSocketFactory = (RMIServerSocketFactory) this.registryClientSocketFactory;
}
if (this.registryClientSocketFactory == null && this.registryServerSocketFactory != null) {
throw new IllegalArgumentException(
"RMIServerSocketFactory without RMIClientSocketFactory for registry not supported");
}
this.createdRegistry = false;
// Determine RMI registry to use.
if (this.registry == null) {
// registry 获取
this.registry = getRegistry(this.registryHost, this.registryPort,
this.registryClientSocketFactory, this.registryServerSocketFactory);
this.createdRegistry = true;
}
// Initialize and cache exported object.
// 初始化并且获取缓存的object
this.exportedObject = getObjectToExport();
if (logger.isDebugEnabled()) {
logger.debug("Binding service '" + this.serviceName + "' to RMI registry: " + this.registry);
}
// Export RMI object.
// 导出RMI object
if (this.clientSocketFactory != null) {
UnicastRemoteObject.exportObject(
this.exportedObject, this.servicePort, this.clientSocketFactory, this.serverSocketFactory);
}
else {
UnicastRemoteObject.exportObject(this.exportedObject, this.servicePort);
}
// Bind RMI object to registry.
// 对象绑定,把serviceName 和 到处的RMI对象进行绑定,JDK实现
try {
if (this.replaceExistingBinding) {
this.registry.rebind(this.serviceName, this.exportedObject);
}
else {
this.registry.bind(this.serviceName, this.exportedObject);
}
}
catch (AlreadyBoundException ex) {
// Already an RMI object bound for the specified service name...
unexportObjectSilently();
throw new IllegalStateException(
"Already an RMI object bound for name '" + this.serviceName + "': " + ex.toString());
}
catch (RemoteException ex) {
// Registry binding failed: let's unexport the RMI object as well.
unexportObjectSilently();
throw ex;
}
}
```
#### checkService
- 校验 service 是否为空
```java
/**
* Check whether the service reference has been set.
*
* 校验service
* @see #setService
*/
protected void checkService() throws IllegalArgumentException {
Assert.notNull(getService(), "Property 'service' is required");
}
```
#### getRegistry
- 获取 Registry 实例
- 简单说就是通过 host 和 port 创建 socket
```java
protected Registry getRegistry(String registryHost, int registryPort,
@Nullable RMIClientSocketFactory clientSocketFactory, @Nullable RMIServerSocketFactory serverSocketFactory)
throws RemoteException {
if (registryHost != null) {
// Host explicitly specified: only lookup possible.
if (logger.isDebugEnabled()) {
logger.debug("Looking for RMI registry at port '" + registryPort + "' of host [" + registryHost + "]");
}
// 通过 host port socket创建
Registry reg = LocateRegistry.getRegistry(registryHost, registryPort, clientSocketFactory);
testRegistry(reg);
return reg;
}
else {
return getRegistry(registryPort, clientSocketFactory, serverSocketFactory);
}
}
```
#### getObjectToExport
- 初始化并且获取缓存的 object
```java
protected Remote getObjectToExport() {
// determine remote object
if (getService() instanceof Remote &&
(getServiceInterface() == null || Remote.class.isAssignableFrom(getServiceInterface()))) {
// conventional RMI service
// 获取service
return (Remote) getService();
}
else {
// RMI invoker
if (logger.isDebugEnabled()) {
logger.debug("RMI service [" + getService() + "] is an RMI invoker");
}
// RMI 包装类
/**
* 1. getProxyForService() 获取代理的接口
* 2. 创建RMI包装对象 RmiInvocationWrapper
*/
return new RmiInvocationWrapper(getProxyForService(), this);
}
}
```
#### getProxyForService
- 获取代理服务
```java
protected Object getProxyForService() {
// service 校验
checkService();
// 校验接口
checkServiceInterface();
// 代理工厂
ProxyFactory proxyFactory = new ProxyFactory();
// 添加代理接口
proxyFactory.addInterface(getServiceInterface());
if (this.registerTraceInterceptor != null ? this.registerTraceInterceptor : this.interceptors == null) {
// 添加切面
proxyFactory.addAdvice(new RemoteInvocationTraceInterceptor(getExporterName()));
}
if (this.interceptors != null) {
AdvisorAdapterRegistry adapterRegistry = GlobalAdvisorAdapterRegistry.getInstance();
for (Object interceptor : this.interceptors) {
proxyFactory.addAdvisor(adapterRegistry.wrap(interceptor));
}
}
// 设置代理类
proxyFactory.setTarget(getService());
proxyFactory.setOpaque(true);
// 获取代理对象
return proxyFactory.getProxy(getBeanClassLoader());
}
```
- 这里要注意,切片方法的`invoke`调用
- `RmiInvocationWrapper`的`invoke`方法会在调用方调用接口时候触发
#### rebind 和 bind
- 绑定和重新绑定
- 这部分源码在: `sun.rmi.registry.RegistryImpl`
```java
public void rebind(String var1, Remote var2) throws RemoteException, AccessException {
checkAccess("Registry.rebind");
this.bindings.put(var1, var2);
}
```
```java
public void bind(String var1, Remote var2) throws RemoteException, AlreadyBoundException, AccessException {
checkAccess("Registry.bind");
synchronized(this.bindings) {
Remote var4 = (Remote)this.bindings.get(var1);
if (var4 != null) {
throw new AlreadyBoundException(var1);
} else {
this.bindings.put(var1, var2);
}
}
}
```
- 共同维护` private Hashtable bindings = new Hashtable(101);`这个对象
#### unexportObjectSilently
- 出现异常时候调用方法
```java
private void unexportObjectSilently() {
try {
UnicastRemoteObject.unexportObject(this.exportedObject, true);
}
catch (NoSuchObjectException ex) {
if (logger.isInfoEnabled()) {
logger.info("RMI object for service '" + this.serviceName + "' is not exported anymore", ex);
}
}
}
```
---
## 客户端初始化
### RmiProxyFactoryBean
- 该类实现了`InitializingBean`接口直接看`afterPropertiesSet`方法
- `org.springframework.remoting.rmi.RmiProxyFactoryBean`
- ```java
@Override
public void afterPropertiesSet() {
super.afterPropertiesSet();
Class ifc = getServiceInterface();
Assert.notNull(ifc, "Property 'serviceInterface' is required");
this.serviceProxy = new ProxyFactory(ifc, this).getProxy(getBeanClassLoader());
}
```
- `org.springframework.remoting.rmi.RmiClientInterceptor#afterPropertiesSet`
- ```java
@Override
public void afterPropertiesSet() {
super.afterPropertiesSet();
prepare();
}
```
- `org.springframework.remoting.support.UrlBasedRemoteAccessor#afterPropertiesSet`
- ```java
@Override
public void afterPropertiesSet() {
if (getServiceUrl() == null) {
throw new IllegalArgumentException("Property 'serviceUrl' is required");
}
}
```
### org.springframework.remoting.support.UrlBasedRemoteAccessor#afterPropertiesSet
- 该方法对 `serviceUrl`进行空判断，如果是空的抛出异常
```java
/**
* 判断服务地址是否为空
*/
@Override
public void afterPropertiesSet() {
if (getServiceUrl() == null) {
throw new IllegalArgumentException("Property 'serviceUrl' is required");
}
}
```
### org.springframework.remoting.rmi.RmiClientInterceptor#afterPropertiesSet
```java
@Override
public void afterPropertiesSet() {
super.afterPropertiesSet();
prepare();
}
```
1. 调用父类的`afterPropertiesSet`方法判断`serviceUrl`是否为空
2. 执行`prepare()`方法
```JAVA
public void prepare() throws RemoteLookupFailureException {
// Cache RMI stub on initialization?
if (this.lookupStubOnStartup) {
// 获取remote对象
Remote remoteObj = lookupStub();
if (logger.isDebugEnabled()) {
if (remoteObj instanceof RmiInvocationHandler) {
logger.debug("RMI stub [" + getServiceUrl() + "] is an RMI invoker");
}
else if (getServiceInterface() != null) {
// 是否接口
boolean isImpl = getServiceInterface().isInstance(remoteObj);
logger.debug("Using service interface [" + getServiceInterface().getName() +
"] for RMI stub [" + getServiceUrl() + "] - " +
(!isImpl ? "not " : "") + "directly implemented");
}
}
if (this.cacheStub) {
this.cachedStub = remoteObj;
}
}
}
```
#### org.springframework.remoting.rmi.RmiClientInterceptor#lookupStub
```JAVA
protected Remote lookupStub() throws RemoteLookupFailureException {
try {
Remote stub = null;
if (this.registryClientSocketFactory != null) {
// RMIClientSocketFactory specified for registry access.
// Unfortunately, due to RMI API limitations, this means
// that we need to parse the RMI URL ourselves and perform
// straight LocateRegistry.getRegistry/Registry.lookup calls.
// 通过 serviceUrl 创建 URL
URL url = new URL(null, getServiceUrl(), new DummyURLStreamHandler());
// url 的协议
String protocol = url.getProtocol();
if (protocol != null && !"rmi".equals(protocol)) {
throw new MalformedURLException("Invalid URL scheme '" + protocol + "'");
}
// 获取host
String host = url.getHost();
// 获取port
int port = url.getPort();
// 获取serviceName
String name = url.getPath();
if (name != null && name.startsWith("/")) {
name = name.substring(1);
}
// 创建 Registry
Registry registry = LocateRegistry.getRegistry(host, port, this.registryClientSocketFactory);
// 获取Remote
stub = registry.lookup(name);
}
else {
// Can proceed with standard RMI lookup API...
stub = Naming.lookup(getServiceUrl());
}
if (logger.isDebugEnabled()) {
logger.debug("Located RMI stub with URL [" + getServiceUrl() + "]");
}
return stub;
}
catch (MalformedURLException ex) {
throw new RemoteLookupFailureException("Service URL [" + getServiceUrl() + "] is invalid", ex);
}
catch (NotBoundException ex) {
throw new RemoteLookupFailureException(
"Could not find RMI service [" + getServiceUrl() + "] in RMI registry", ex);
}
catch (RemoteException ex) {
throw new RemoteLookupFailureException("Lookup of RMI stub failed", ex);
}
}
```
### org.springframework.remoting.rmi.RmiProxyFactoryBean#afterPropertiesSet
```java
@Override
public void afterPropertiesSet() {
super.afterPropertiesSet();
// 获取 服务提供的接口
Class ifc = getServiceInterface();
// 如果服务接口不为空
Assert.notNull(ifc, "Property 'serviceInterface' is required");
// 创建服务代理
this.serviceProxy = new ProxyFactory(ifc, this).getProxy(getBeanClassLoader());
}
```
### 增强调用
- 通过类图我们可以知道`RmiProxyFactoryBean`实现了`MethodInterceptor`,具体实现方法在`org.springframework.remoting.rmi.RmiClientInterceptor#invoke`
```JAVA
@Override
public Object invoke(MethodInvocation invocation) throws Throwable {
// 获取remote
Remote stub = getStub();
try {
// 真正的invoke调用
return doInvoke(invocation, stub);
}
catch (RemoteConnectFailureException ex) {
return handleRemoteConnectFailure(invocation, ex);
}
catch (RemoteException ex) {
if (isConnectFailure(ex)) {
return handleRemoteConnectFailure(invocation, ex);
}
else {
throw ex;
}
}
}
```
```JAVA
protected Remote getStub() throws RemoteLookupFailureException {
if (!this.cacheStub || (this.lookupStubOnStartup && !this.refreshStubOnConnectFailure)) {
// 如果缓存stub存在直接获取,否则创建
return (this.cachedStub != null ? this.cachedStub : lookupStub());
}
else {
synchronized (this.stubMonitor) {
if (this.cachedStub == null) {
this.cachedStub = lookupStub();
}
return this.cachedStub;
}
}
}
```
- `org.springframework.remoting.rmi.RmiClientInterceptor#doInvoke(org.aopalliance.intercept.MethodInvocation, org.springframework.remoting.rmi.RmiInvocationHandler)`
```JAVA
@Nullable
protected Object doInvoke(MethodInvocation methodInvocation, RmiInvocationHandler invocationHandler)
throws RemoteException, NoSuchMethodException, IllegalAccessException, InvocationTargetException {
if (AopUtils.isToStringMethod(methodInvocation.getMethod())) {
return "RMI invoker proxy for service URL [" + getServiceUrl() + "]";
}
/**
* 1. 参数组装成对象{@link RemoteInvocationBasedAccessor#createRemoteInvocation(org.aopalliance.intercept.MethodInvocation)}
* 2. invoke 执行 简单来说就是调用{@link RmiInvocationHandler#invoke(RemoteInvocation)}方法
*/
return invocationHandler.invoke(createRemoteInvocation(methodInvocation));
}
```
- `RmiInvocationHandler`类图
最后的`invoke`方法
- `org.springframework.remoting.rmi.RmiInvocationWrapper#invoke`
```JAVA
/**
* Delegates the actual invocation handling to the RMI exporter.
*
*
* 远程调用的时候会执行
* @see RmiBasedExporter#invoke(org.springframework.remoting.support.RemoteInvocation, Object)
*/
@Override
@Nullable
public Object invoke(RemoteInvocation invocation)
throws RemoteException, NoSuchMethodException, IllegalAccessException, InvocationTargetException {
return this.rmiExporter.invoke(invocation, this.wrappedObject);
}
```
- 继续跟踪`org.springframework.remoting.rmi.RmiBasedExporter#invoke`
```JAVA
@Override
protected Object invoke(RemoteInvocation invocation, Object targetObject)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
return super.invoke(invocation, targetObject);
}
```
- 继续跟踪`org.springframework.remoting.support.RemoteInvocationBasedExporter#invoke`
```JAVA
protected Object invoke(RemoteInvocation invocation, Object targetObject)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
if (logger.isTraceEnabled()) {
logger.trace("Executing " + invocation);
}
try {
return getRemoteInvocationExecutor().invoke(invocation, targetObject);
}
catch (NoSuchMethodException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Could not find target method for " + invocation, ex);
}
throw ex;
}
catch (IllegalAccessException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Could not access target method for " + invocation, ex);
}
throw ex;
}
catch (InvocationTargetException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Target method failed for " + invocation, ex.getTargetException());
}
throw ex;
}
}
```
- 关键语句**`return getRemoteInvocationExecutor().invoke(invocation, targetObject);`**
类图
```JAVA
public class DefaultRemoteInvocationExecutor implements RemoteInvocationExecutor {
@Override
public Object invoke(RemoteInvocation invocation, Object targetObject)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
Assert.notNull(invocation, "RemoteInvocation must not be null");
Assert.notNull(targetObject, "Target object must not be null");
return invocation.invoke(targetObject);
}
}
```
```JAVA
public Object invoke(Object targetObject)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
Method method = targetObject.getClass().getMethod(this.methodName, this.parameterTypes);
return method.invoke(targetObject, this.arguments);
}
```
- 这部分流程相对清晰,从对象中获取函数,调用这个函数
---
## 服务端 debug
- `org.springframework.remoting.rmi.RmiServiceExporter#afterPropertiesSet`打上断点
可以看到此时的数据字段和我们的 xml 配置中一致
- `org.springframework.remoting.rmi.RmiServiceExporter#prepare`断点
往下一直走
这一行是 jdk 的就不进去看了
执行完成就创建出了 `Registry`
- `org.springframework.remoting.rmi.RmiBasedExporter#getObjectToExport`
直接看结果对象
- 执行 bind
- 此时服务端信息已经成功记录并且启动
## 客户端 debug
remote 对象
- 服务提供接口
- serviceProxy
- 方法调用
- 使用的是 AOP 技术进行的，AOP 相关技术不在此处展开
stub 对象
- `invocation`
- `targetObject`
- 反射执行`method`结束整个调用
此时得到结果 RMI 调用结束