1、Spring中,HTTPInvoker(HTTP调用器)是通过基于HTTP协议的分布式远程调用解决方案,和java RMI一样,HTTP调用器也需要使用java的对象序列化机制完成客户端和服务器端的通信。HTTP调用器的远程调用工作原理如下:
(1)客户端:
a、向服务器发送远程调用请求:
远程调用信息——>封装为远程调用对象——>序列化写入到远程调用HTTP请求中——>向服务器端发送。
b、接收服务器端返回的远程调用结果:
服务器端返回的远程调用结果HTTP响应——>反序列化为远程调用结果对象。
(2)服务器端:
a、接收客户端发送的远程调用请求:
客户端发送的远程调用HTTP请求——>反序列化为远程调用对象——>调用服务器端目标对象的目标方法处理。
b、向客户端返回远程调用结果:
服务器端目标对象方法的处理结果——>序列化写入远程调用结果HTTP响应中——>返回给客户端。
接下来我们将从客户端和服务器端分别分析HTTP调用器远程调用的具体实现。
2、HTTP调用器客户端配置:
使用HTTP调用器之前,首先需要对客户端进行如下配置:
在HTTP调用器客户端代理HttpInvokeProxyFactoryBean中封装远程调用服务URL和服务接口,客户端程序通过HTTP调用代理可以调用实现了指定接口的目标服务端对象。
3、HttpInvokeProxyFactoryBean创建远程调用代理对象:
HTTP调用器客户端代理HttpInvokeProxyFactoryBean是一个实现了Spring FactoryBean接口的IoC容器,其作用是对远程服务客户端封装,源码如下:
public class HttpInvokerProxyFactoryBean extends HttpInvokerClientInterceptor implements FactoryBean
//远程对象的代理
private Object serviceProxy;
//在IoC容器注入完成之后调用
public void afterPropertesSet(){
//调用父类容器的回调方法
super.afterPropertiesSet();
//getServiceInterface()方法用于获取配置的远程调用接口
if(getServiceInterface() == null){
throw new IllegalArgumentException("Property 'serviceInterface' is required");
}
//使用ProxyFactory代理工厂生成远程代理对象,注意第二个参数this,因为HttpInvokerProxyFactoryBean继承了HttpInvokerClientInterceptor,
//所以代理对象的拦截器设置为HttpInvokerClientInterceptor
this.serviceProxy = new ProxyFactory(getServiceInterface(),this).getProxy(getBeanClassLoader());
}
//向IoC容器索取被管理对象的方法,获取产生的远程调用代理对象
public Object getObject(){
return this.serviceProxy;
}
//获取对象类型,返回配置的远程调用接口
public Class getObjectType(){
return getServiceInterface();
}
//是否是单态类型,默认Spring IoC容器产生的都是单态类型
public boolean isSingleton(){
return true;
}
}
通过上面对HttpInvokerProxyFactoryBean源码的分析我们看到,当通过getObject方法向Spring IoC容器索取远程调用对象是,触发afterPropertiesSet回调方法,创建远程调用的代理对象,最后将该远程调用对象返回。在创建远程调用代理对象时,使用其父类HttpInvokerClientInterceptor作为远程调用代理对象的拦截器,该拦截器将拦截对代理对象的方法调用。下面我们分析HttpInvokerClientInterceptor代理拦截器对代理对象的方法拦截处理。
4、HttpInvokerClientInterceptor拦截对远程调用代理的方法调用:
当客户端通过HTTP请求调用远程调用代理的方法时,将会触发HttpInvokerClientInterceptor拦截器的invoke方法对当前的请求进行封装处理,将客户端的java对象序列化传输到服务器端,在远程服务器端执行完请求之后,又将处理结果java对象序列化返回给客户端。其源码如下:
public class HttpInvokerClientInterceptor extends RemoteInvocationBasedAccessor implements MethodInterceptor,HttpInvokerClientConfiguration {
private String codebaseUrl;
//HTTP调用请求执行器
private HttpInvokerRequestExecutor httpInvokerRequestExecutor;
public void setCodebaseUrl(String codebaseUrl) {
this.codebaseUrl = codebaseUrl;
}
public String getCodebaseUrl(){
return this.codebaseUrl;
}
public void setHttpInvokerRequestExecutor(HttpInvokerRequestExecutor httpInokerRequestExecutor){
this.httpInvokerRequestExecutor = httpInvokerRequestExecutor;
}
//获取HTTP定义请求执行器,如果HTTP定义请求执行器没有设置,则使用SimpleHttpInvokerRequestExecutor作为HTTP调用请求执行器
public HttpInvokerRequestExecutor getHttpInvokerRequestExecutor(){
if(this.httpInvokerRequestExecutor == null){
SimpleHttpInvokerRequestExecutor executor = new SimpleHttpInvokerRequestExecutor();
executor.setBeanClassLoader(getBeanClassLoader());
this.httpInvokerRequestExecutor = executor;
}
return this.httpInvokerRequestExecutor;
}
//IoC容器初始化完成回调方法
public void afterPropertiesSet(){
//调用父类的初始化回调方法
super.afterPropertiesSet();
//获取HTTP调用请求执行器
getHttpInvokerRequestExecutor();
}
//拦截器代理对象方法调用入口,拦截器将客户端对远程调用代理的调用封装为MethodInvocation对象
public Object invoke(MethodInvocation methodInvocation) throws Throwable {
if(AopUtis.isToStringMethod(methodInvocation.getMethod())){
return "HTTP invoker proxy for service URL [" + getServiceUrl() + "]";
}
//创建远程调用对象,封装了远程调用
RemoteInvocation invocation = createRemoteInvocation(methodInvocation);
//远程调用结果
RemoteInvocationResult result = null;
try{
//远程调用入口
result = executeRequest(invocation,methodInvocation);
}
catch(Throwable ex){
throw converHttpInvokerAccessException(ex);
}
try{
//返回远程调用结果
return recreateRemoteInvocationResult(result);
}
catch(Throwable ex){
if(result.hasInvocationTargetException()){
throw ex;
}
else{
throw new RemoteInvocationFailureException("Invocation of method [" + methodInvocation.getMethod() +
"] failed in HTTP invoker remote service at [ " + getServiceUrl() + "] ", ex);
}
}
}
//执行远程调用入口
protected RemoteInvocationResult executeRequest(RemoteInvocation invocation,MethodInvocation originalInvocation) throws Exception {
return executeRequest(invocation);
}
//通过HTTP调用请求执行器执行远程调用
protected RemoteInvocationResult executeRequest(RemoteInvocation invocation) throws Exception {
return getHttpInvokerRequestExecutor().executeRequest(this,invocation);
}
//将远程调用异常转换成Spring异常
protected RemoteAccessException convertHttpInvokerAccessException(Throwable ex){
if(ex instanceof ConnectException){
throw new RemoteConnectFailureException("Could not connect to HTTP invoker remote service at [" + getServiceUrl() + "]",ex);
}
else if(ex instanceof ClassNotFoundException || ex instanceof NoClassDefFoundError || ex instanceof InvalidClassException){
throw new RemoteAccessException("Could not deserialize result from HTTP invoker remote service [" + getServiceUrl() + "]" ,ex);
}
else{
throw new RemoteAccessException("Could not access HTTP invoker remote service at [" + getServiceUrl() + "]",ex);
}
}
}
通过上面对HttpInvokerClientInterceptor拦截器的源码分析,我们可以看出,拦截器将客户端对远程调用的HTTP请求封装成了MethodInvocation对象,拦截器在调用远程调用的代理对象时,又将方法调用封装成了RemoteInvocation远程调用,RemoteInvocation数据对象中封装了调用的具体信息,如方法名、方法参数以及参数类型等。
真正执行远程调用的是HTTP调用请求执行器SimpleHttpInvokerRequestExecutor,下面我们继续分析SimpleHttpInvokerRequestExecutor远程调用的具体过程。
5、SimpleHttpInvokerRequestExecutor远程调用:
SimpleHttpInvokerRequestExecutor封装了基于HTTP协议的远程调用过程,具体源码如下:
public class SimpleHttpInvokerRequestExecutor extends AbstractHttpInvokerRequestExecutor{
//HTTP调用请求执行器真正进行远程调用的方法,该方法有由其父类AbstractHttpInvokerRequestExecutor的executeRequest方法调用
protected RemoteInvocationResult doExecuteRequest(HttpInvokerClientConfiguration config,ByteArrayOutputStream baos) throws IOException,ClassNotFoundException{
//打开一个标准的J2SE HttpURLConnection
HttpURLConnection con = openConnection(config);
//准备连接
prepareConnection(con,baos.size());
//远程调用被封装成了RemoteInvocation对象,它通过序列化被写到对应的HttpURLConnection中
writeRequestBody(config,con,baos);
//获取远程调用的结果,校验返回的结果
validateResponse(config,con);
InputStream responseBody = readResponseBody(config,con);
//将远程调用结果转换成RemoteInvocationResult返回
return readRemoteInocationResult(responseBody,config.getCodebaseUrl());
}
//打开一个HttpURLConnection
protoected HttpURLConnection openConnection(HttpInvokerClientConfiguration config) throws IOException {
//getServiceUrl()方法获取配置的远程调用URL,打开一个URL连接
URLConnection con = new URL(config.getServiceUrl()).openConnection();
if(!(con instanceof HttpURLConnection)){
throw new IOException("Service URL [" + config.getServiceUrl() + "] is not an HTTP URL");
}
return (HttpURLConnection) con;
}
//准备HTTP请求连接
protected void prepareConnection(HttpURLConnection con,int contentLength) throws IOException {
con.setDoOutput(true);
//HTTP调用器只支持POST请求方法
con.setRequestMethod(HTTP_METHOD_POST);
//设置HTTP请求头内容类型,设置为:application/x -java-serialized-object
con.setRequestProperty(HTTP_HEADER_CONTENT_TYPE,getContentType());
//设置HTTP请求头内容长度
con.setRequestProperty(HTTP_HEADER_CONTENT_LENGTH,Integer.toString(contentLength));
LocalContext local = LocalContextHolder.getLocalContext();
//设置HTTP请求的Local
if(local != null){
con.setRequestProperty(HTTP_HEADER_ACCEPT_LANGUAGE,StringUtils.toLanguageTag(local.getLocal()));
}
//设置HTTP请求压缩方式
if(isAcceptGzipEncoding()){
con.setRequestProperty(HTTP_HEADER_ACCEPT_ENCODING,ENCODING_GZIP);
}
}
//把序列化对象输出到HTTP请求体中
protected void writeRequestBody(HttpInvokerClientConfiguration config,HttpURLConnection con,ByteArrayOutputStream baos) throws IOException {
baos.writeTo(con.getOutputStream());
}
//校验远程调用的HTTP响应
protected void validateResponse(HttpInvokerClientConfiguration config,HttpURLConnection con) throws IOException {
//如果HTTP响应状态码大于等于300,则证明调用发生错误
if(con.getResponseCode() >= 300){
throw new IOException("Did not receive successful HTTP response: status code = " + con.getResponseCode() +
", status message = [" + con.getResponseMessage() + "]");
}
}
//提取远程调用结果的HTTP响应信息
protected InputStream readResponseBody(HttpInvokerClientConfiguration config,HttpURLConnection con) throws IOException {
//如果响应信息是GZIP压缩的,则需要先解压
if(isGzipResponse(con)){
return new GZIPInputStream(con.getInputStream());
}
//正常的HTTP响应
else{
return con.getInputStream();
}
}
//是否是Gzip格式压缩
protected boolean isGzipResponse(HttpURLConnection con) {
//获取HTTP响应头信息中的压缩方式
String encodingHeader = con.getHeaderField(HTTP_HEADER_CONTENT_ENCODING);
return (encodingHeader != null && encodingHeader.toLowerCase().indexOf(ENCODING_GZIP) != -1);
}
}
通过对SimpleHttpInvokerRequestExecutor的分析,我们看到,HTTP调用请求执行器的处理逻辑是:首先,打开指定的URL的HTTP连接,设置连接属性。其次,将封装请求的RemoteInvocation对象序列化到请求体中,HTTP请求发送到服务器端。最后,从服务器端的HTTP响应中读取输入流,并将响应结果转换成RemoteInvocationResult。
将远程调用的HTTP响应转换为RemoteInvocationResult是由AbstractHttpInvokerRequestExecutor的readRemoteInvocationResult方法实现,下面我们将分析其将HTTP响应结果转换成RemoteInvocationResult的实现。
6、AbstractHttpInvokerRequestExecutor将HTTP响应结果转换成RemoteInvocationResult:
AbstractHttpInvokerRequestExecutor中处理远程调用结果,并将HTTP响应转换成RemoteInvocationResult的主要方法如下:
//从HTTP响应中读取远程调用结果入口方法
protected RemoteInvocationResult readRemoteInvocationResult(InputStream is,String codebaseUrl) throws IOException,ClassNotFoundException {
//根据给定的输入流和类创建对象输入流
ObjectInputStream ois = createObjectInputStream(decorateInputStream(is),codebaseUrl);
try{
//从对象输入流中读取远程调用结果
return doReadRemoteInvocationResult(ois);
}
finally{
ois.close();
}
}
//从对象输入流中读取远程调用结果
protected RemoteInvocationResult doReadRemoteInvocationResult(ObjectInputStream ois) throws IOException,ClassNotFoundException {
//获取对象输入流中的对象
Object obj = ois.readObject();
if(!(obj instanceof RemoteInvocationResult)){
throw new RemoteException("Deserialized object needs to be assignable to type [" + RemoteInvocationResult.class.getName() + "]: " + obj);
}
//将获取到的对象封装为RemoteInvocationResult
return (RemoteInvocationResult) obj;
}
7、HTTP调用器的服务器端配置:
和HTTP调用器客户端类似,服务器端也需要进行如下的配置:
通过对服务器端配置的列子,我们可以看出,真正处理远程调用的服务器实现是由service属性中指定的服务器端bean提供的,HttpInvokerServiceExporter将远程调用服务接口和服务实现类进行封装,主要提供HTTP协议封装和java对象序列化功能。
Spring的HttpInvokerServiceExporter是与Spring的MVC结合在一起的,它本质上是Spring MVC的一个Controller,客户端发来的远程调用HTTP请求由Spring MVC的中央控制器DispatcherServlet转发到指定的URL的HttpInvokerServiceExporter上。
8、HttpInvokerServiceExporter导出和执行远程调用服务:
HttpInvokerServcieExporter响应客户端发送的远程调用HTTP请求,它从HTTP请求中读取远程调用并将其反序列化为RemoteInvocation对象,然后调用目标服务对象的目标方法完成远程调用服务,当服务执行完成之后,通过HTTP响应把执行结果对象序列化输出到客户端。其源码如下:
public class HttpInvokerServiceExporter extends RemoteInvocationSerializingExporter implements HttpRequestHandler {
//处理客户端发来的远程调用HTTP请求
public void handRequest(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException {
try{
//从HTTP请求中反序列化出RemoteInvocation远程调用对象
RemoteInvocation invocation = readRemoteInvocation(request);
//调用目标服务对象,完成远程调用请求,并创建调用结果
RemoteInvocationResult result = invokeAndCreateResult(invocation,getProxy());
//将调用结果写到HTTP响应中
writeRemoteInvocationResult(request,response,result);
}
catch(ClassNotFoundException ex){
throw new NestedServletException("Class not found during deserialization",ex);
}
}
//从HTTP请求中读取RemoteInvocation远程调用对象入口方法
protected RemoteInvocation readRemoteInvocation(HttpServletRequest request) throws IOException,ClassNotFoundException {
//将从HTTP请求中读取远程调用对象
return readRemoteInvocation(request,request.getInputStream());
}
//从HTTP请求中读取远程调用对象
protected RemoteInvocation readRemoteInvocation(HttpServletRequest request,InputStream is) throws IOException,ClassNotFoundException {
//根据HTTP请求输入流创建对象输入流
ObjectInputStream ois = createObjectInputStream(decorateInputStream(request,is));
try{
//从对象输入流中读取远程调用对象
return doReadRemoteInvocation(ois);
}
finally{
ois.close();
}
}
//获取HTTP请求输入流
protected InputStream decorateInputStream(HttpServletRequest request,InputStream is) throws IOException {
return is;
}
//将远程调用执行结果写到HTTP响应中
protected void writeRemoteInvocationRequest(HttpServletRequest request,HttpServletRespose respose,RemoteInvocationResult result) throws IOException {
//设置HTTP响应的内容类型为:application/x -java-serialized-object
respose.setContentType(getContentType());
//将远程调用结果写到HTTP响应中
writeRemoteInvocationResult(request,response,result,response.getOutputStream());
}
//将远程调用执行结果写入HTTP响应中
protected void writeRemoteInvocationResult(HttpServletRequest request,HttpServeltResponse response,RemoteInvocationResult result,OutputStream os)
throws IOException {
//获取HTTP响应对象输出流
ObjectOutputStream oos = createObjectOutputStream(decorateOutputStream(request,response,os));
try{
//将远程调用执行结果写到HTTP响应对象输出流中
doWriteRemoteInvocationResult(result,oos);
}
finally{
oos.close();
}
}
//获取HTTP响应对象输入流
protected OutputStream decorateOutputStream(HttpServletRequest request,HttpServletRespose response,OutputStream os) throws IOException {
return os;
}
}
通过对HttpInvokerServiceExporter的源码分析,我们可以看出,真正执行远程对象调用的是RemoteInvocationResult = invokeAndCreateResult(invocation,getProxy());它调用了RemoteInvocationBasedExporter的invokerAndCreateResult方法调用远程目标对象方法,并创建远程调用执行结果,下面我们继续分析执行服务器端远程调用目标对象方法的实现。
9、RemoteInvocationBasedExporter调用服务器目标对象:
RemoteInvocationBasedExporter的invokeAndCreateResult方法调用服务器目标对象方法,RemoteInvocationBasedExporter源码如下:
public abstract class RemoteInvocationBasedExporter extends RemoteExporter {
//远程调用执行器
private RemoteInvocationExecutor remoteInvocationExecutor = new DefaultRemoteInvocationExecutor();
public RemoteInvocationExecutor getRemoteInvocationExecutor(){
return this.remoteInvocationExecutor;
}
protected RemoteInvocationResult invokeAndCreateResult(RemoteInvocation invocation,Object targetObject) {
try{
//调用服务器端目标对象的方法
Object value = invoke(invocation,targetObject);
//根据执行结果创建RemoteInvocationResult
return new RemoteInvocationResult(value);
}
catch(Throwable ex){
return new RemoteInvocationResult(ex);
}
}
//调用目标对象的方法
protected Object invoke(RemoteInvocation invocation,Object targetObject) throws NoSuchMethodException,IllegalAccessException,InvocationTargetException {
if(logger.isTraceEnabled()){
logger.trace("Executing " + invocation);
}
try{
//获取远程调用执行器,由远程调用执行器调用目标对象的方法,即通过DefaultRemoteInvocationExecutor来调用目标对象的方法
return getRemoteInvocationExecutor().invoke(invocation,targetObject);
}
catch(NoSuchMethodException ex){
if(logger.isDebugEnabled()){
logger.warn("Could not find target method for "+ invocation,ex);
}
throw ex;
}
catch(InvocationTargetException ex){
if(logger.isDebugEnabled()){
logger.debug("Target method failed for " + invocation,ex.getTargetException());
}
throw ex;
}
}
}
通过上面对RemoteInvocationBasedExporter源码分析我们看到,真正调用目标对象的是DefaultRemoteInvocationExecutor的invoke方法,下面我们继续分析DefaultRemoteInvocationExecutor调用目标对象方法的实现。
10、DefaultRemoteInvocationExecutor调用目标对象的方法实现远程调用:
DefaultRemoteInvocationExecutor用于调用目标对象的指定方法实现远程对象调用服务,其源码如下:
public class DefaultRemoteInvocationExecutor implements RemoteInvocationExecutor {
//调用目标对象的方法
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");
//调用RemoteInvocation的invoke方法
return invocation.invoke(targetObject);
}
}
RemoteInvocation的invoke方法源码如下:
public Object invoke(Object targetObject) throws NoSuchMethodException,IllegalAccessException,InvocationTargetException {
//获取远程调用对象的方法名称和参数类型
Method method = targetObject.getClass().getMethod(this.methodName,this.parameterTypes);
//利用JDK反射机制,调用目标对象指定参数的方法
return method.invoke(targetObject,this.arguments);
}