Spring的HTTPInvoker
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，首先需要对客户端其进行如下的配置：
<!--客户端HTTP调用器代理-->
<beanid=”proxy” class=”org.springframework.remoting.httpinvoker.HttpInvokerProxyFactoryBean”>
<propertyname=”serviceUrl”>
<value>http://yourhost:8080/远程调用URL</value>
</property>
<propertyname=”serviceInterface”>
<value>远程调用服务接口全路径</value>
</property>
</bean>
<beanid=”客户端bean” class=”客户端Bean全路径”>
<propertyname=”remoteService”>
<refbean=”proxy”/>
</property>
</bean>
在HTTP调用器客户端代理HttpInvokerProxyFactoryBean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.HttpInvokerProxyFactoryBean创建远程调用代理对象：
HTTP调用器客户端代理HttpInvokerProxyFactoryBean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：
publicclass HttpInvokerProxyFactoryBean extends HttpInvokerClientInterceptor implements FactoryBean<Object> {
//远程对象的代理
private Object serviceProxy;
//在IoC容器注入完成之后调用
publicvoid afterPropertiesSet() {
//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) {
thrownew 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() {
returnthis.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
publicboolean isSingleton() {
returntrue;
}
}
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时，触发afterPropertiesSet回调方法，创建远程调用的代理对象，最后将该远程调用代理对象返回。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:
publicclass HttpInvokerClientInterceptor extends RemoteInvocationBasedAccessor
implements MethodInterceptor, HttpInvokerClientConfiguration {
private String codebaseUrl;
//HTTP调用请求执行器
private HttpInvokerRequestExecutor httpInvokerRequestExecutor;
publicvoid setCodebaseUrl(String codebaseUrl) {
this.codebaseUrl = codebaseUrl;
}
public String getCodebaseUrl() {
returnthis.codebaseUrl;
}
publicvoid setHttpInvokerRequestExecutor(HttpInvokerRequestExecutor httpInvokerRequestExecutor) {
this.httpInvokerRequestExecutor = httpInvokerRequestExecutor;
}
//获取HTTP调用请求执行器，如果HTTP调用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;
}
returnthis.httpInvokerRequestExecutor;
}
//IoC容器初始化完成回调方法
publicvoid 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 (AopUtils.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 convertHttpInvokerAccessException(ex);
}
try {
//返回远程调用结果
return recreateRemoteInvocationResult(result);
}
catch (Throwable ex) {
if (result.hasInvocationTargetException()) {
throw ex;
}
else {
thrownew 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) {
thrownew RemoteConnectFailureException(
"Could not connect to HTTP invoker remote service at [" + getServiceUrl() + "]", ex);
}
elseif (ex instanceof ClassNotFoundException || ex instanceof NoClassDefFoundError ||
ex instanceof InvalidClassException) {
thrownew RemoteAccessException(
"Could not deserialize result from HTTP invoker remote service [" + getServiceUrl() + "]", ex);
}
else {
thrownew 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，拦截器的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：
publicclass 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 readRemoteInvocationResult(responseBody, config.getCodebaseUrl());
}
//打开一个HttpURLConnection
protected 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)) {
thrownew IOException("Service URL [" + config.getServiceUrl() + "] is not an HTTP URL");
}
return (HttpURLConnection) con;
}
//准备HTTP请求连接
protectedvoid 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));
LocaleContext locale = LocaleContextHolder.getLocaleContext();
//设置HTTP请求的Locale
if (locale != null) {
con.setRequestProperty(HTTP_HEADER_ACCEPT_LANGUAGE, StringUtils.toLanguageTag(locale.getLocale()));
}
//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
protectedvoid writeRequestBody(
HttpInvokerClientConfiguration config, HttpURLConnection con, ByteArrayOutputStream baos)
throws IOException {
baos.writeTo(con.getOutputStream());
}
//校验远程调用的HTTP响应
protectedvoid 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) {
thrownew 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)) {
returnnew GZIPInputStream(con.getInputStream());
}
//正常的HTTP响应
else {
return con.getInputStream();
}
}
//是否是Gzip格式压缩
protectedboolean 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，请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其将HTTP响应结果转换成RemoteInvocationResult：
AbstractHttpInvokerRequestExecutor中处理远程调用结果，并HTTP响应转换为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)) {
thrownew 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：
<beanname=”/客户端配置的远程调用URL” class=”org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter”>
<propertyname=”service”>
<refbean=”服务器端实现bean”/>
</property>
<propertyname=”serviceInterface”>
<value>远程调用服务接口全路径</value>
</property>
</property>
通过对服务器端配置的例子，我们可以看出，真正处理远程调用的服务器端实现是由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请求有Spring MVC的中央控制器DispatcherServlet转发到指定URL的HttpInvokerServiceExporter上。
8.HttpInvokerServiceExporter导出和执行远程调用服务：
HttpInvokerServiceExporter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。器源码如下：
publicclass HttpInvokerServiceExporter extends RemoteInvocationSerializingExporter implements HttpRequestHandler {
//处理客户端发来的远程调用HTTP请求
publicvoid handleRequest(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) {
thrownew 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
protectedvoid writeRemoteInvocationResult(
HttpServletRequest request, HttpServletResponse response, RemoteInvocationResult result) throws IOException {
//设置HTTP响应的内容类型为：application/x-java-serialized-object
response.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
protectedvoid writeRemoteInvocationResult(
HttpServletRequest request, HttpServletResponse 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, HttpServletResponse 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RemoteInvocationResultresult = invokeAndCreateResult(invocation, getProxy());它调用了RemoteInvocationBasedExporter的invokeAndCreateResult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：
publicabstractclass RemoteInvocationBasedExporter extends RemoteExporter {
//远程调用执行器
private RemoteInvocationExecutor remoteInvocationExecutor = new DefaultRemoteInvocationExecutor();
public RemoteInvocationExecutor getRemoteInvocationExecutor() {
returnthis.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
returnnew RemoteInvocationResult(value);
}
catch (Throwable ex) {
returnnew 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了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 (IllegalAccessException ex) {
if (logger.isDebugEnabled()) {
logger.warn("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;
}
}
}
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：
publicclass 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);
}