[深入剖析Tomcat]一個簡單的servlet容器實現
阿新 • • 發佈：2019-01-29
本文為讀《深入剖析Tomcat》第2章做的筆記、寫的程式碼、做的分析。作者是菜鳥，謹慎參考
實現流程圖
HttpServer類：
public class HttpServer1 {
private static String SHUT_DOWN="shutdown";
public static void main(String[] args){
HttpServer1 server=new HttpServer1();
server.await();
}
private void await() {
ServerSocket server=null 3 . Response類的主要方法
public class Response implements ServletResponse {
private OutputStream out;
private Request req;
private static int BUFFER_SIZE = 1024;
public Response(OutputStream out) {
this.out = out;
}
public void setRequest(Request req) {
this.req = req;
}
public void sendStaticReSource() throws IOException {
System.out.println("訪問的資源為"+Constants.WEB_ROOT + req.getUri());
File file = new File(Constants.WEB_ROOT + req.getUri());
FileInputStream fis = null;
byte[] buffer = new byte[1024];
int n = -1;
try {
if (file.exists()) {
System.out.println("該資源存在");
fis = new FileInputStream(file);
n = fis.read(buffer, 0, BUFFER_SIZE);
while (n != -1) {
out.write(buffer, 0, n);
n = fis.read(buffer, 0, BUFFER_SIZE);
}
} else {
System.out.println("該資源不存在");
String msg = "msg error! file does not exist.";
out.write(msg.getBytes());
}
} catch (IOException e) {
}finally{
if(fis!=null)
fis.close();
}
}
public PrintWriter getWriter() throws IOException{
//呼叫println會自動重新整理，呼叫print不會自動重新整理
PrintWriter writer =new PrintWriter(out,true);
return writer;
}
}4 . Request的主要方法：
public class Request implements ServletRequest{
private final static int BUFFER_SIZE=2048;
private InputStream input;
private String uri;
public Request(InputStream input) {
this.input=input;
}
public void parse() {
byte[] buffers=new byte[BUFFER_SIZE];
int n;
try {
n = input.read(buffers, 0, BUFFER_SIZE);
} catch (IOException e) {
e.printStackTrace();
n=-1;
}
StringBuffer sb=new StringBuffer();
for(int i=0;i<n;i++){
sb.append((char)buffers[i]);
}
System.out.println("解析得到request：");
System.out.println(sb);
uri=parseUri(sb.toString());
System.out.println("解析request中的uri："+uri);
}
private String parseUri(String str){
int index1,index2;
index1=str.indexOf(' ');
while(index1!=-1){
index2=str.indexOf(' ', index1+1);
if(index2-index1>0)
return str.substring(index1+1,index2);
}
return null;
}
public String getUri(){
return uri;
}
}- ServletProcessor類：
public class ServletProcessor1 {
public void process(Request req,Response res){
String uri =req.getUri();
String servletName=uri.substring(uri.lastIndexOf('/')+1);
//URLCLassLoader為ClassLoader的直接子類
//用它的loadClass（）方法來載入servlet類
URLClassLoader loader=null;
try {
URL[] urls=new URL[1];
URLStreamHandler streamHandler=null;
File classPath=new File(Constants.WEB_ROOT);
String repository=(new URL("file",null,classPath.getCanonicalPath()
+File.separator)).toString();
System.out.println("servlet的目錄repository："+repository);
//使用streamHandler的因為URL過載中，第3個引數不同
//streamHandler將其區分，repository為servlet的目錄
urls[0]=new URL(null,repository,streamHandler);
//urls為URL物件陣列，每個URL物件都指明瞭類載入器在哪裡查詢類
//若URL以“/”結尾，則表明其指向一個目錄，否則為指向一個jar檔案
//根據需要載入器會下載這個jar檔案
//在servlet容器中，類載入器查詢servlet類的目錄稱作倉庫（repository）
loader=new URLClassLoader(urls);
} catch (IOException e) {
e.printStackTrace();
}
Class myclass=null;
try {
System.out.println("需要載入的 servletName："+servletName);
myclass=loader.loadClass(servletName);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
Servlet servlet=null;
try {
servlet=(Servlet) myclass.newInstance();
servlet.service(req, res);
} catch (Exception e) {
e.printStackTrace();
}
}
}6 . 需要注意的兩點：
1）第一點需要注意的：在ServletProcessor類的process(Request req,Response res)中如下寫是不好的，因為在service(ServletRequest req, ServletResponse res)方法中，可以將req下轉型為Request型，從而req可以訪問parse方法，可以將res下轉型為Request型，從而res可以訪問sendStaticResource()方法：
servlet=(Servlet) myclass.newInstance();
servlet.service(req, res);2）針對上一點的改進方法，增加ResponseFacade類如下圖：
3）將上1）步的程式碼改為如下，為什麼這樣能避免不好的情況，在下一篇文章中舉例說明：
servlet=(Servlet) myclass.newInstance();
RequestFacade requestFacade=new RequestFacade(req);
ResponseFacade responseFacade=new ResponseFacade(res);
servlet.service(requestFacade, responseFacade);4）第2個需要注意的問題，如下圖，ServletResponse為介面，3）中servlet.service(requestFacade, responseFacade)會呼叫被訪問servletName類的service(ServletRequest req, ServletResponse res)方法，例如儘管res是ServletResponse 例項，當使用res.getWriter()，實際上呼叫的是Response類中重寫的getWriter()：
