Added readonly version of HttpHeaders

org.springframework.web/src/main/java/org/springframework/http/HttpHeaders.java

 /*
- * Copyright 2002-2009 the original author or authors.
+ * Copyright 2002-2010 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,13 +26,13 @@ import java.util.Collections;
 import java.util.Date;
 import java.util.EnumSet;
 import java.util.Iterator;
+import java.util.LinkedHashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.TimeZone;
-import java.util.LinkedHashMap;
 
 import org.springframework.util.Assert;
 import org.springframework.util.LinkedCaseInsensitiveMap;
@@ -93,9 +93,40 @@ public class HttpHeaders implements MultiValueMap<String, String> {
 
 	private static TimeZone GMT = TimeZone.getTimeZone("GMT");
 
+	private final Map<String, List<String>> headers;
+
+	/**
+	 * Private constructor that can create read-only {@code HttpHeader} instances.
+	 */
+	private HttpHeaders(Map<String, List<String>> headers, boolean readOnly) {
+		Assert.notNull(headers, "'headers' must not be null");
+		if (readOnly) {
+			Map<String, List<String>> map =
+					new LinkedCaseInsensitiveMap<List<String>>(headers.size(), Locale.ENGLISH);
+			for (Entry<String, List<String>> entry : headers.entrySet()) {
+				List<String> values = Collections.unmodifiableList(entry.getValue());
+				map.put(entry.getKey(), values);
+			}
+			this.headers = Collections.unmodifiableMap(map);
+		}
+		else {
+			this.headers = headers;
+		}
+	}
 
-	private final Map<String, List<String>> headers = new LinkedCaseInsensitiveMap<List<String>>(8);
+	/**
+	 * Constructs a new instance of the {@code HttpHeaders} object.
+	 */
+	public HttpHeaders() {
+		this(new LinkedCaseInsensitiveMap<List<String>>(8, Locale.ENGLISH), false);
+	}
 
+	/**
+	 * Returns {@code HttpHeaders} object that can only be read, not written to.
+	 */
+	public static HttpHeaders readOnlyHttpHeaders(HttpHeaders headers) {
+		return new HttpHeaders(headers, true);
+	}
 
 	/**
 	 * Set the list of acceptable {@linkplain MediaType media types}, as specified by the {@code Accept} header.

org.springframework.web/src/main/java/org/springframework/http/client/AbstractClientHttpRequest.java

 /*
- * Copyright 2002-2009 the original author or authors.
+ * Copyright 2002-2010 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,8 +20,8 @@ import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
 
-import org.springframework.util.Assert;
 import org.springframework.http.HttpHeaders;
+import org.springframework.util.Assert;
 
 /**
  * Abstract base for {@link ClientHttpRequest} that makes sure that headers and body are not written multiple times.
@@ -39,8 +39,7 @@ public abstract class AbstractClientHttpRequest implements ClientHttpRequest {
 
 
 	public final HttpHeaders getHeaders() {
-		checkExecuted();
-		return this.headers;
+		return executed ? HttpHeaders.readOnlyHttpHeaders(headers) : this.headers;
 	}
 
 	public final OutputStream getBody() throws IOException {

org.springframework.web/src/main/java/org/springframework/http/server/ServletServerHttpResponse.java

 /*
- * Copyright 2002-2009 the original author or authors.
+ * Copyright 2002-2010 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,9 +22,9 @@ import java.util.List;
 import java.util.Map;
 import javax.servlet.http.HttpServletResponse;
 
-import org.springframework.util.Assert;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
+import org.springframework.util.Assert;
 
 /**
  * {@link ServerHttpResponse} implementation that is based on a {@link HttpServletResponse}.
@@ -56,7 +56,7 @@ public class ServletServerHttpResponse implements ServerHttpResponse {
 	}
 
 	public HttpHeaders getHeaders() {
-		return this.headers;
+		return headersWritten ? HttpHeaders.readOnlyHttpHeaders(headers) : this.headers;
 	}
 
 	public OutputStream getBody() throws IOException {

org.springframework.web/src/test/java/org/springframework/http/client/AbstractHttpRequestFactoryTestCase.java

 /*
- * Copyright 2002-2009 the original author or authors.
+ * Copyright 2002-2010 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -124,7 +124,7 @@ public abstract class AbstractHttpRequestFactoryTestCase {
 		}
 	}
 
-	@Test(expected = IllegalStateException.class)
+	@Test(expected = UnsupportedOperationException.class)
 	public void headersAfterExecute() throws Exception {
 		ClientHttpRequest request = factory.createRequest(new URI(BASE_URL + "/echo"), HttpMethod.POST);
 		request.getHeaders().add("MyHeader", "value");