blocks|key|1038692|text|以下是我快速编写的内容；我相信它还可以改进。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1038693|import+java.util.*;
import+java.io.UnsupportedEncodingException;
import+java.net.URLEncoder;

public+class+MapQuery+{
++++static+String+urlEncodeUTF8(String+s)+{
++++++++try+{
++++++++++++return+URLEncoder.encode(s,+"UTF-8");
++++++++}+catch+(UnsupportedEncodingException+e)+{
++++++++++++throw+new+UnsupportedOperationException(e);
++++++++}
++++}
++++static+String+urlEncodeUTF8(Map<?,?>+map)+{
++++++++StringBuilder+sb+=+new+StringBuilder();
++++++++for+(Map.Entry<?,?>+entry+:+map.entrySet())+{
++++++++++++if+(sb.length()+>+0)+{
++++++++++++++++sb.append("&");
++++++++++++}
++++++++++++sb.append(String.format("%25s=%25s",
++++++++++++++++urlEncodeUTF8(entry.getKey().toString()),
++++++++++++++++urlEncodeUTF8(entry.getValue().toString())
++++++++++++));
++++++++}
++++++++return+sb.toString();+++++++
++++}
++++public+static+void+main(String[]+args)+{
++++++++Map<String,Object>+map+=+new+HashMap<String,Object>();
++++++++map.put("p1",+12);
++++++++map.put("p2",+"cat");
++++++++map.put("p3",+"a+&+b");+++++++++
++++++++System.out.println(urlEncodeUTF8(map));
++++++++//+prints+"p3=a%2B%2526%2Bb&p2=cat&p1=12"
++++}
}|code-block|syntax|javascript|1038694|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here's something that I quickly wrote; I'm sure it can be improved upon.

<pre><code>import java.util.*;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;

public class MapQuery {
 static String urlEncodeUTF8(String s) {
 try {
 return URLEncoder.encode(s, "UTF-8");
 } catch (UnsupportedEncodingException e) {
 throw new UnsupportedOperationException(e);
 }
 }
 static String urlEncodeUTF8(Map&lt;?,?&gt; map) {
 StringBuilder sb = new StringBuilder();
 for (Map.Entry&lt;?,?&gt; entry : map.entrySet()) {
 if (sb.length() &gt; 0) {
 sb.append("&amp;");
 }
 sb.append(String.format("%s=%s",
 urlEncodeUTF8(entry.getKey().toString()),
 urlEncodeUTF8(entry.getValue().toString())
 ));
 }
 return sb.toString(); 
 }
 public static void main(String[] args) {
 Map&lt;String,Object&gt; map = new HashMap&lt;String,Object&gt;();
 map.put("p1", 12);
 map.put("p2", "cat");
 map.put("p3", "a &amp; b"); 
 System.out.println(urlEncodeUTF8(map));
 // prints "p3=a+%26+b&amp;p2=cat&amp;p1=12"
 }
}
</code></pre>

blocks|key|1253726|text|我看到的最健壮的是来自Apache+Http+Compoments+(HttpClient+4.0)的URLEncodedUtils类。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1253727|URLEncodedUtils.format()方法就是您所需要的。|style|CODE|1253728|它不使用map，因此您可以使用重复的参数名，例如，|1253729|++a=1&a=2&b=3|code-block|syntax|javascript|1253730|我并不推荐使用这种类型的参数名。|1253731|entityMap|0|LINK|mutability|MUTABLE|url|http://hc.apache.org/|1|http://hc.apache.org/httpcomponents-client-4.3.x/httpclient/apidocs/org/apache/http/client/utils/URLEncodedUtils.html^0|B|M|0|1F|F|1|0|0|O|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]|$A|14|B|15|1|16]]|C|$]]|$1|D|3|E|5|6|7|17|8|@$A|18|B|19|F|G]]|9|@]|C|$]]|$1|H|3|I|5|6|7|1A|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|1B|8|@]|9|@]|C|$M|N]]|$1|O|3|P|5|6|7|1C|8|@]|9|@]|C|$]]|$1|Q|3|-4|5|6|7|1D|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]]]

The most robust one I saw off-the-shelf is the <a href="http://hc.apache.org/httpcomponents-client-4.3.x/httpclient/apidocs/org/apache/http/client/utils/URLEncodedUtils.html" rel="noreferrer">URLEncodedUtils</a> class from <a href="http://hc.apache.org/" rel="noreferrer">Apache Http Compoments</a> (HttpClient 4.0).

The method <code>URLEncodedUtils.format()</code> is what you need.

It doesn't use map so you can have duplicate parameter names, like,

<pre><code> a=1&amp;a=2&amp;b=3
</code></pre>

Not that I recommend this kind of use of parameter names.

blocks|key|1253761|text|如果您实际上想构建一个完整的URI，可以尝试使用Apache+Http+Compoments中的URIBuilder+(HttpClient+4)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1253762|这实际上没有回答这个问题，但它回答了我发现这个问题时的问题。|1253763|entityMap|0|LINK|mutability|MUTABLE|url|http://hc.apache.org/|1|http://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/org/apache/http/client/utils/URIBuilder.html^0|O|M|0|1C|A|1|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]|$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|X|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]|N|$5|I|J|K|C|$L|O]]]]

If you actually want to build a complete URI, try <a href="http://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/org/apache/http/client/utils/URIBuilder.html" rel="noreferrer">URIBuilder</a> from <a href="http://hc.apache.org/" rel="noreferrer">Apache Http Compoments</a> (HttpClient 4).

This does not actually answer the question, but it answered the one I had when I found this question.

blocks|key|1253843|text|另一种'one+class‘/无依赖关系的方式，处理单个/多个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1253844|import+java.io.UnsupportedEncodingException;
import+java.net.URLEncoder;
import+java.util.ArrayList;
import+java.util.Arrays;
import+java.util.Iterator;
import+java.util.LinkedHashMap;
import+java.util.List;
import+java.util.Map;
import+java.util.Map.Entry;

public+class+UrlQueryString+{
++private+static+final+String+DEFAULT_ENCODING+=+"UTF-8";

++public+static+String+buildQueryString(final+LinkedHashMap<String,+Object>+map)+{
++++try+{
++++++final+Iterator<Map.Entry<String,+Object>>+it+=+map.entrySet().iterator();
++++++final+StringBuilder+sb+=+new+StringBuilder(map.size()+*+8);
++++++while+(it.hasNext())+{
++++++++final+Map.Entry<String,+Object>+entry+=+it.next();
++++++++final+String+key+=+entry.getKey();
++++++++if+(key+!=+null)+{
++++++++++sb.append(URLEncoder.encode(key,+DEFAULT_ENCODING));
++++++++++sb.append('=');
++++++++++final+Object+value+=+entry.getValue();
++++++++++final+String+valueAsString+=+value+!=+null+?+URLEncoder.encode(value.toString(),+DEFAULT_ENCODING)+:+"";
++++++++++sb.append(valueAsString);
++++++++++if+(it.hasNext())+{
++++++++++++sb.append('&');
++++++++++}
++++++++}+else+{
++++++++++//+Do+what+you+want...for+example:
++++++++++assert+false+:+String.format("Null+key+in+query+map:+%25s",+map.entrySet());
++++++++}
++++++}
++++++return+sb.toString();
++++}+catch+(final+UnsupportedEncodingException+e)+{
++++++throw+new+UnsupportedOperationException(e);
++++}
++}

++public+static+String+buildQueryStringMulti(final+LinkedHashMap<String,+List<Object>>+map)+{
++++try+{
++++++final+StringBuilder+sb+=+new+StringBuilder(map.size()+*+8);
++++++for+(final+Iterator<Entry<String,+List<Object>>>+mapIterator+=+map.entrySet().iterator();+mapIterator.hasNext();)+{
++++++++final+Entry<String,+List<Object>>+entry+=+mapIterator.next();
++++++++final+String+key+=+entry.getKey();
++++++++if+(key+!=+null)+{
++++++++++final+String+keyEncoded+=+URLEncoder.encode(key,+DEFAULT_ENCODING);
++++++++++final+List<Object>+values+=+entry.getValue();
++++++++++sb.append(keyEncoded);
++++++++++sb.append('=');
++++++++++if+(values+!=+null)+{
++++++++++++for+(final+Iterator<Object>+listIt+=+values.iterator();+listIt.hasNext();)+{
++++++++++++++final+Object+valueObject+=+listIt.next();
++++++++++++++sb.append(valueObject+!=+null+?+URLEncoder.encode(valueObject.toString(),+DEFAULT_ENCODING)+:+"");
++++++++++++++if+(listIt.hasNext())+{
++++++++++++++++sb.append('&');
++++++++++++++++sb.append(keyEncoded);
++++++++++++++++sb.append('=');
++++++++++++++}
++++++++++++}
++++++++++}
++++++++++if+(mapIterator.hasNext())+{
++++++++++++sb.append('&');
++++++++++}
++++++++}+else+{
++++++++++//+Do+what+you+want...for+example:
++++++++++assert+false+:+String.format("Null+key+in+query+map:+%25s",+map.entrySet());
++++++++}
++++++}
++++++return+sb.toString();
++++}+catch+(final+UnsupportedEncodingException+e)+{
++++++throw+new+UnsupportedOperationException(e);
++++}
++}

++public+static+void+main(final+String[]+args)+{
++++//+Examples:+could+be+turned+into+unit+tests+...
++++{
++++++final+LinkedHashMap<String,+Object>+queryItems+=+new+LinkedHashMap<String,+Object>();
++++++queryItems.put("brand",+"C&A");
++++++queryItems.put("count",+null);
++++++queryItems.put("misc",+42);
++++++final+String+buildQueryString+=+buildQueryString(queryItems);
++++++System.out.println(buildQueryString);
++++}
++++{
++++++final+LinkedHashMap<String,+List<Object>>+queryItems+=+new+LinkedHashMap<String,+List<Object>>();
++++++queryItems.put("usernames",+new+ArrayList<Object>(Arrays.asList(new+String[]+{+"bob",+"john"+})));
++++++queryItems.put("nullValue",+null);
++++++queryItems.put("misc",+new+ArrayList<Object>(Arrays.asList(new+Integer[]+{+1,+2,+3+})));
++++++final+String+buildQueryString+=+buildQueryStringMulti(queryItems);
++++++System.out.println(buildQueryString);
++++}
++}
}|code-block|syntax|javascript|1253845|当需要时，您可以使用简单的(在大多数情况下更容易编写)或多个。请注意，两者可以通过添加一个“与”号组合在一起...如果你发现任何问题，请在评论中告诉我。|1253846|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Another 'one class'/no dependency way of doing it, handling single/multiple:

<pre><code>import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

public class UrlQueryString {
 private static final String DEFAULT_ENCODING = "UTF-8";

 public static String buildQueryString(final LinkedHashMap&lt;String, Object&gt; map) {
 try {
 final Iterator&lt;Map.Entry&lt;String, Object&gt;&gt; it = map.entrySet().iterator();
 final StringBuilder sb = new StringBuilder(map.size() * 8);
 while (it.hasNext()) {
 final Map.Entry&lt;String, Object&gt; entry = it.next();
 final String key = entry.getKey();
 if (key != null) {
 sb.append(URLEncoder.encode(key, DEFAULT_ENCODING));
 sb.append('=');
 final Object value = entry.getValue();
 final String valueAsString = value != null ? URLEncoder.encode(value.toString(), DEFAULT_ENCODING) : "";
 sb.append(valueAsString);
 if (it.hasNext()) {
 sb.append('&amp;');
 }
 } else {
 // Do what you want...for example:
 assert false : String.format("Null key in query map: %s", map.entrySet());
 }
 }
 return sb.toString();
 } catch (final UnsupportedEncodingException e) {
 throw new UnsupportedOperationException(e);
 }
 }

 public static String buildQueryStringMulti(final LinkedHashMap&lt;String, List&lt;Object&gt;&gt; map) {
 try {
 final StringBuilder sb = new StringBuilder(map.size() * 8);
 for (final Iterator&lt;Entry&lt;String, List&lt;Object&gt;&gt;&gt; mapIterator = map.entrySet().iterator(); mapIterator.hasNext();) {
 final Entry&lt;String, List&lt;Object&gt;&gt; entry = mapIterator.next();
 final String key = entry.getKey();
 if (key != null) {
 final String keyEncoded = URLEncoder.encode(key, DEFAULT_ENCODING);
 final List&lt;Object&gt; values = entry.getValue();
 sb.append(keyEncoded);
 sb.append('=');
 if (values != null) {
 for (final Iterator&lt;Object&gt; listIt = values.iterator(); listIt.hasNext();) {
 final Object valueObject = listIt.next();
 sb.append(valueObject != null ? URLEncoder.encode(valueObject.toString(), DEFAULT_ENCODING) : "");
 if (listIt.hasNext()) {
 sb.append('&amp;');
 sb.append(keyEncoded);
 sb.append('=');
 }
 }
 }
 if (mapIterator.hasNext()) {
 sb.append('&amp;');
 }
 } else {
 // Do what you want...for example:
 assert false : String.format("Null key in query map: %s", map.entrySet());
 }
 }
 return sb.toString();
 } catch (final UnsupportedEncodingException e) {
 throw new UnsupportedOperationException(e);
 }
 }

 public static void main(final String[] args) {
 // Examples: could be turned into unit tests ...
 {
 final LinkedHashMap&lt;String, Object&gt; queryItems = new LinkedHashMap&lt;String, Object&gt;();
 queryItems.put("brand", "C&amp;A");
 queryItems.put("count", null);
 queryItems.put("misc", 42);
 final String buildQueryString = buildQueryString(queryItems);
 System.out.println(buildQueryString);
 }
 {
 final LinkedHashMap&lt;String, List&lt;Object&gt;&gt; queryItems = new LinkedHashMap&lt;String, List&lt;Object&gt;&gt;();
 queryItems.put("usernames", new ArrayList&lt;Object&gt;(Arrays.asList(new String[] { "bob", "john" })));
 queryItems.put("nullValue", null);
 queryItems.put("misc", new ArrayList&lt;Object&gt;(Arrays.asList(new Integer[] { 1, 2, 3 })));
 final String buildQueryString = buildQueryStringMulti(queryItems);
 System.out.println(buildQueryString);
 }
 }
}
</code></pre>

You may use either simple (easier to write in most cases) or multiple when required. Note that both can be combined by adding an ampersand...
If you find any problems let me know in the comments.

blocks|key|1253895|text|在Spring+Util中，有一种更好的方法..|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1253896|import+org.springframework.util.LinkedMultiValueMap;
import+org.springframework.util.MultiValueMap;
import+org.springframework.util.concurrent.ListenableFuture;
import+org.springframework.web.util.UriComponents;
import+org.springframework.web.util.UriComponentsBuilder;

MultiValueMap<String,+String>+params+=+new+LinkedMultiValueMap<String,+String>();
params.add("key",+key);
params.add("storeId",+storeId);
params.add("orderId",+orderId);
UriComponents+uriComponents+=+++++UriComponentsBuilder.fromHttpUrl("http://spsenthil.com/order").queryParams(params).build();
ListenableFuture<ResponseEntity<String>>+responseFuture+=+++++restTemplate.getForEntity(uriComponents.toUriString(),+String.class);|code-block|syntax|javascript|1253897|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

In Spring Util, there is a better way..,

<pre><code>import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.web.util.UriComponents;
import org.springframework.web.util.UriComponentsBuilder;

MultiValueMap&lt;String, String&gt; params = new LinkedMultiValueMap&lt;String, String&gt;();
params.add("key", key);
params.add("storeId", storeId);
params.add("orderId", orderId);
UriComponents uriComponents = UriComponentsBuilder.fromHttpUrl("http://spsenthil.com/order").queryParams(params).build();
ListenableFuture&lt;ResponseEntity&lt;String&gt;&gt; responseFuture = restTemplate.getForEntity(uriComponents.toUriString(), String.class);
</code></pre>

blocks|key|1038976|text|我找到了一个使用java8和polygenelubricants解决方案的平滑解决方案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1038977|parameters.entrySet().stream()
++++.map(p+->+urlEncodeUTF8(p.getKey())+%2B+"="+%2B+urlEncodeUTF8(p.getValue()))
++++.reduce((p1,+p2)+->+p1+%2B+"&"+%2B+p2)
++++.orElse("");|code-block|syntax|javascript|1038978|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I found a smooth solution using java 8 and polygenelubricants' solution.

<pre><code>parameters.entrySet().stream()
 .map(p -&gt; urlEncodeUTF8(p.getKey()) + "=" + urlEncodeUTF8(p.getValue()))
 .reduce((p1, p2) -&gt; p1 + "&amp;" + p2)
 .orElse("");
</code></pre>

blocks|key|1253995|text|这是我使用Java8和org.apache.http.client.URLEncodedUtils实现的解决方案。它将映射的条目映射为BasicNameValuePair列表，然后使用Apache的URLEncodedUtils将其转换为查询字符串。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1253996|List<BasicNameValuePair>+nameValuePairs+=+params.entrySet().stream()
+++.map(entry+->+new+BasicNameValuePair(entry.getKey(),+entry.getValue()))
+++.collect(Collectors.toList());

URLEncodedUtils.format(nameValuePairs,+Charset.forName("UTF-8"));|code-block|syntax|javascript|1253997|entityMap^0|B|12|1V|I|2R|F|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

This is the solution I implemented, using Java 8 and <code>org.apache.http.client.URLEncodedUtils</code>. It maps the entries of the map into a list of <code>BasicNameValuePair</code> and then uses Apache's <code>URLEncodedUtils</code> to turn that into a query string.

<pre><code>List&lt;BasicNameValuePair&gt; nameValuePairs = params.entrySet().stream()
 .map(entry -&gt; new BasicNameValuePair(entry.getKey(), entry.getValue()))
 .collect(Collectors.toList());

URLEncodedUtils.format(nameValuePairs, Charset.forName("UTF-8"));
</code></pre>

blocks|key|1254075|text|在@eclipse的基础上改进一下:在Javaland中，请求参数映射通常表示为一个Map<String,+String[]>，一个Map<String,+List<String>>，或者可能是某种类似的MultiValueMap<String,+String>。在任何情况下:一个参数通常可以有多个值。因此，Java+8解决方案应该是这样的：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1254076|public+String+getQueryString(HttpServletRequest+request,+String+encoding)+{
++++Map<String,+String[]>+parameters+=+request.getParameterMap();

++++return+parameters.entrySet().stream()
++++++++++++.flatMap(entry+->+encodeMultiParameter(entry.getKey(),+entry.getValue(),+encoding))
++++++++++++.reduce((param1,+param2)+->+param1+%2B+"&"+%2B+param2)
++++++++++++.orElse("");
}

private+Stream<String>+encodeMultiParameter(String+key,+String[]+values,+String+encoding)+{
++++return+Stream.of(values).map(value+->+encodeSingleParameter(key,+value,+encoding));
}

private+String+encodeSingleParameter(String+key,+String+value,+String+encoding)+{
++++return+urlEncode(key,+encoding)+%2B+"="+%2B+urlEncode(value,+encoding);
}

private+String+urlEncode(String+value,+String+encoding)+{
++++try+{
++++++++return+URLEncoder.encode(value,+encoding);
++++}+catch+(UnsupportedEncodingException+e)+{
++++++++throw+new+IllegalArgumentException("Cannot+url+encode+"+%2B+value,+e);
++++}
}|code-block|syntax|javascript|1254077|entityMap^0|16|L|1U|P|2U|T|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

To improve a little bit upon @eclipse's answer: In Javaland a request parameter map is usually represented as a <code>Map&lt;String, String[]&gt;</code>, a <code>Map&lt;String, List&lt;String&gt;&gt;</code> or possibly some kind of <code>MultiValueMap&lt;String, String&gt;</code> which is sort of the same thing. In any case: a parameter can usually have multiple values. A Java 8 solution would therefore be something along these lines:

<pre><code>public String getQueryString(HttpServletRequest request, String encoding) {
 Map&lt;String, String[]&gt; parameters = request.getParameterMap();

 return parameters.entrySet().stream()
 .flatMap(entry -&gt; encodeMultiParameter(entry.getKey(), entry.getValue(), encoding))
 .reduce((param1, param2) -&gt; param1 + "&amp;" + param2)
 .orElse("");
}

private Stream&lt;String&gt; encodeMultiParameter(String key, String[] values, String encoding) {
 return Stream.of(values).map(value -&gt; encodeSingleParameter(key, value, encoding));
}

private String encodeSingleParameter(String key, String value, String encoding) {
 return urlEncode(key, encoding) + "=" + urlEncode(value, encoding);
}

private String urlEncode(String value, String encoding) {
 try {
 return URLEncoder.encode(value, encoding);
 } catch (UnsupportedEncodingException e) {
 throw new IllegalArgumentException("Cannot url encode " + value, e);
 }
}
</code></pre>

blocks|key|1039237|text|我想在@eclipse的答案的基础上使用java8映射和还原。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1039238|+protected+String+formatQueryParams(Map<String,+String>+params)+{
++++++return+params.entrySet().stream()
++++++++++.map(p+->+p.getKey()+%2B+"="+%2B+p.getValue())
++++++++++.reduce((p1,+p2)+->+p1+%2B+"&"+%2B+p2)
++++++++++.map(s+->+"?"+%2B+s)
++++++++++.orElse("");
++}|code-block|syntax|javascript|1039239|额外的map操作接受简化后的字符串，并仅当该字符串存在时才将?放在前面。|offset|length|style|CODE|1039240|entityMap^0|0|0|3|3|U|1|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

I wanted to build on @eclipse's answer using java 8 mapping and reducing.

<pre><code> protected String formatQueryParams(Map&lt;String, String&gt; params) {
 return params.entrySet().stream()
 .map(p -&gt; p.getKey() + "=" + p.getValue())
 .reduce((p1, p2) -&gt; p1 + "&amp;" + p2)
 .map(s -&gt; "?" + s)
 .orElse("");
 }
</code></pre>

The extra <code>map</code> operation takes the reduced string and puts a <code>?</code> in front only if the string exists.

blocks|key|1039341|text|java中没有内置的东西可以做到这一点。但是，嘿，java是一种编程语言，所以..让我们对它进行编程吧！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1039342|map.entrySet().stream().map(e+->+e.getKey()+%2B+"="+%2B+e.getValue()).collect(Collectors.joining("&"))|code-block|syntax|javascript|1039343|这就是"param1=12¶m2=cat“。现在，我们需要将URL和这一部分连接在一起。你可能认为你可以这样做：URL+%2B+"?"+%2B+theAbove，但是如果URL已经包含了一个问号，你必须用"&“将它连接起来。检查的一种方法是查看URL中的某个位置是否已经有问号。|offset|length|style|CODE|1039344|另外，我也不太清楚你的地图上有什么。如果是原始数据，您可能需要使用URLEncoder.encode或类似的方法来保护对e.getKey()和e.getValue()的调用。|1039345|还有另一种方法是你有更宽广的视野。您是否正在尝试将地图的内容附加到URL，或者...您是否正在尝试从java进程发出HTTP(S)请求，并将map中的内容作为(附加的)+HTTP参数？在后一种情况下，你可以查看像OkHttp这样的http库，它有一些很好的API来做这项工作，然后你可以放弃任何需要在第一个地方弄乱这个网址。|1039346|entityMap|0|LINK|mutability|MUTABLE|url|https://square.github.io/okhttp/^0|0|0|1K|K|0|X|H|1O|A|1Z|C|0|2Y|6|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@$I|11|J|12|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|13|8|@$I|14|J|15|K|L]|$I|16|J|17|K|L]|$I|18|J|19|K|L]]|9|@]|A|$]]|$1|O|3|P|5|6|7|1A|8|@]|9|@$I|1B|J|1C|1|1D]]|A|$]]|$1|Q|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

There's nothing built into java to do this. But, hey, java is a programming language, so.. let's program it!
<pre><code>map.entrySet().stream().map(e -&gt; e.getKey() + &quot;=&quot; + e.getValue()).collect(Collectors.joining(&quot;&amp;&quot;))
</code></pre>
This gives you &quot;param1=12&amp;param2=cat&quot;. Now we need to join the URL and this bit together. You'd think you can just do: <code>URL + &quot;?&quot; + theAbove</code> but if the URL already contains a question mark, you have to join it all together with &quot;&amp;&quot; instead. One way to check is to see if there's a question mark in the URL someplace already.
Also, I don't quite know what is in your map. If it's raw stuff, you probably have to safeguard the call to <code>e.getKey()</code> and <code>e.getValue()</code> with <code>URLEncoder.encode</code> or similar.
Yet another way to go is that you take a wider view. Are you trying to append a map's content to a URL, or... are you trying to make an HTTP(S) request from a java process with the stuff in the map as (additional) HTTP params? In the latter case, you can look into an http library like <a href="https://square.github.io/okhttp/" rel="nofollow noreferrer">OkHttp</a> which has some nice APIs to do this job, then you can forego any need to mess about with that URL in the first place.

blocks|key|1254352|text|就我个人而言，我会选择这样的解决方案，它与@rzwitserloot提供的解决方案非常相似，只是有细微的区别。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1254353|这个解决方案很小，简单而且干净，它只需要很少的依赖项，所有这些都是Java+Util包的一部分。|1254354|Map<String,+String>+map+=+new+HashMap<>();

map.put("param1",+"12");
map.put("param2",+"cat");

String+output+=+"someUrl?";
output+%2B=+map.entrySet()
++++.stream()
++++.map(x+->+x.getKey()+%2B+"="+%2B+x.getValue()+%2B+"&")
++++.collect(Collectors.joining("&"));

System.out.println(output.substring(0,+output.length()+-1));|code-block|syntax|javascript|1254355|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Personally, I'd go for a solution like this, it's incredibly similar to the solution provided by @rzwitserloot, only subtle differences. 

This solution is small, simple &amp; clean, it requires very little in terms of dependencies, all of which are a part of the Java Util package.

<pre><code>Map&lt;String, String&gt; map = new HashMap&lt;&gt;();

map.put("param1", "12");
map.put("param2", "cat");

String output = "someUrl?";
output += map.entrySet()
 .stream()
 .map(x -&gt; x.getKey() + "=" + x.getValue() + "&amp;")
 .collect(Collectors.joining("&amp;"));

System.out.println(output.substring(0, output.length() -1));
</code></pre>

blocks|key|1039453|text|使用EntrySet和Streams：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1039454|map
++.entrySet()
++.stream()
++.map(e+->+e.getKey()+%2B+"="+%2B+e.getValue())
++.collect(Collectors.joining("&"));|code-block|syntax|javascript|1039455|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Using EntrySet and Streams: 

<pre><code>map
 .entrySet()
 .stream()
 .map(e -&gt; e.getKey() + "=" + e.getValue())
 .collect(Collectors.joining("&amp;"));
</code></pre>

blocks|key|1039509|text|为此，您可以使用Stream，但我将使用Uri.Builder，而不是自己附加查询参数。例如：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1039510|final+Map<String,+String>+map+=+new+HashMap<>();
map.put("param1",+"cat");
map.put("param2",+"12");

final+Uri+uri+=+
++++map.entrySet().stream().collect(
++++++++()+->+Uri.parse("relativeUrl").buildUpon(),
++++++++(builder,+e)+->+builder.appendQueryParameter(e.getKey(),+e.getValue()),
++++++++(b1,+b2)+->+{+throw+new+UnsupportedOperationException();+}
++++).build();

//Or,+if+you+consider+it+more+readable...
final+Uri.Builder+builder+=+Uri.parse("relativeUrl").buildUpon();
map.entrySet().forEach(e+->+builder.appendQueryParameter(e.getKey(),+e.getValue())
final+Uri+uri+=+builder.build();

//...++++

assertEquals(Uri.parse("relativeUrl?param1=cat&param2=12"),+uri);|code-block|syntax|javascript|1039511|entityMap^0|8|6|K|B|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

You can use a <code>Stream</code> for this, but instead of appending query parameters myself I'd use a <code>Uri.Builder</code>. For example:

<pre><code>final Map&lt;String, String&gt; map = new HashMap&lt;&gt;();
map.put("param1", "cat");
map.put("param2", "12");

final Uri uri = 
 map.entrySet().stream().collect(
 () -&gt; Uri.parse("relativeUrl").buildUpon(),
 (builder, e) -&gt; builder.appendQueryParameter(e.getKey(), e.getValue()),
 (b1, b2) -&gt; { throw new UnsupportedOperationException(); }
 ).build();

//Or, if you consider it more readable...
final Uri.Builder builder = Uri.parse("relativeUrl").buildUpon();
map.entrySet().forEach(e -&gt; builder.appendQueryParameter(e.getKey(), e.getValue())
final Uri uri = builder.build();

//... 

assertEquals(Uri.parse("relativeUrl?param1=cat&amp;param2=12"), uri);
</code></pre>

blocks|key|1254498|text|我认为这在内存使用和性能方面更好，并且我只想在值为空时发送属性名。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1254499|public+static+String+toUrlEncode(Map<String,+Object>+map)+{
++++StringBuilder+sb+=+new+StringBuilder();
++++map.entrySet().stream()
++++++++++++.forEach(entry
++++++++++++++++++++->+(entry.getValue()+==+null
++++++++++++++++++++?+sb.append(entry.getKey())
++++++++++++++++++++:+sb.append(entry.getKey())
++++++++++++++++++++++++++++.append('=')
++++++++++++++++++++++++++++.append(URLEncoder.encode(entry.getValue().toString(),+StandardCharsets.UTF_8)))
++++++++++++++++++++.append('&')
++++++++++++);
++++sb.delete(sb.length()+-+1,+sb.length());
++++return+sb.toString();
}|code-block|syntax|javascript|1254500|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I think this is better for memory usage and performance, and I want to send just the property name when the value is null.

<pre><code>public static String toUrlEncode(Map&lt;String, Object&gt; map) {
 StringBuilder sb = new StringBuilder();
 map.entrySet().stream()
 .forEach(entry
 -&gt; (entry.getValue() == null
 ? sb.append(entry.getKey())
 : sb.append(entry.getKey())
 .append('=')
 .append(URLEncoder.encode(entry.getValue().toString(), StandardCharsets.UTF_8)))
 .append('&amp;')
 );
 sb.delete(sb.length() - 1, sb.length());
 return sb.toString();
}
</code></pre>

blocks|key|1254545|text|对于多值映射，您可以像下面这样做(使用java+8流api)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1254546|Url编码已经在这方面得到了重视。|1254547|MultiValueMap<String,+String>+params+=++new+LinkedMultiValueMap<>();
String+urlQueryString+=+params.entrySet()
++++++++++++.stream()
++++++++++++.flatMap(stringListEntry+->+stringListEntry.getValue()
++++++++++++++++++++.stream()
++++++++++++++++++++.map(s+->+UriUtils.encode(stringListEntry.getKey(),+StandardCharsets.UTF_8.toString())+%2B+"="+%2B
++++++++++++++++++++++++++++UriUtils.encode(s,+StandardCharsets.UTF_8.toString())))
++++++++++++.collect(Collectors.joining("&"));|code-block|syntax|javascript|1254548|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

For multivalue map you can do like below (using java 8 stream api's)
Url encoding has been taken cared in this.
<pre><code>MultiValueMap&lt;String, String&gt; params = new LinkedMultiValueMap&lt;&gt;();
String urlQueryString = params.entrySet()
 .stream()
 .flatMap(stringListEntry -&gt; stringListEntry.getValue()
 .stream()
 .map(s -&gt; UriUtils.encode(stringListEntry.getKey(), StandardCharsets.UTF_8.toString()) + &quot;=&quot; +
 UriUtils.encode(s, StandardCharsets.UTF_8.toString())))
 .collect(Collectors.joining(&quot;&amp;&quot;));
</code></pre>

blocks|key|1254558|text|Kotlin|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1254559|mapOf(
++"param1"+to+12,
++"param2"+to+"cat"
).map+{+"${it.key}=${it.value}"+}
++.joinToString("&")|code-block|syntax|javascript|1254560|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Kotlin
<pre><code>mapOf(
 &quot;param1&quot; to 12,
 &quot;param2&quot; to &quot;cat&quot;
).map { &quot;${it.key}=${it.value}&quot; }
 .joinToString(&quot;&amp;&quot;)
</code></pre>

blocks|key|1254574|text|下面是一个简单的kotlin解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1254575|fun+Map<String,+String>.toUrlParams():+String+=
++++entries.joinToString("&")+{
++++++++it.key.toUrlEncoded()+%2B+"="+%2B+it.value.toUrlEncoded()
++++}

fun+String.toUrlEncoded():+String+=+URLEncoder.encode(
++++this,+StandardCharsets.UTF_8
)|code-block|syntax|javascript|1254576|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here's a simple kotlin solution:
<pre><code>fun Map&lt;String, String&gt;.toUrlParams(): String =
 entries.joinToString(&quot;&amp;&quot;) {
 it.key.toUrlEncoded() + &quot;=&quot; + it.value.toUrlEncoded()
 }

fun String.toUrlEncoded(): String = URLEncoder.encode(
 this, StandardCharsets.UTF_8
)
</code></pre>

Do you know of any utility class/library, that can convert Map into URL-friendly query string?

Example:

I have a map:

<pre><code>"param1"=12,
"param2"="cat"
</code></pre>

I want to get: 

<pre><code>param1=12&amp;param2=cat
</code></pre>

final output

<pre><code>relativeUrl+param1=12&amp;param2=cat
</code></pre>

How to convert map to url query string?

Kotlin

Java

您知道有什么实用程序类/库可以将Map转换为URL友好的查询字符串吗？示例：我有张地图："param1"=12,"param2"="cat"我想要得到：param1=12&param2=cat最终输出relativeUrl+param1=12&param2=cat

问如何将map转换为url查询字符串？
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问如何将map转换为url查询字符串？
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