如何在java中有效解析查询参数？

Question

All I have is the request URI from which I have to parse the query params. What I'm doing is adding them to json/hashmap and fetching again like the following

String requestUri = "name=raju&school=abcd&college=mnop&color=black&fruit=mango";

All I have to do is to finally assign it to variables like the following

String name = "raju";
String school = "abcd";
String college = "mnop";
String color = "black";
String fruit = "mango";

So I am parsing the request uri like the following

String[] paramsKV = requestUri.split("&");
JSONArray jsonKVArr = new JSONArray();
for (String params : paramsKV) {
    String[] tempArr = params.split("=");
    if(tempArr.length>1) {
        String key = tempArr[0];
        String value = tempArr[1];
        JSONObject jsonObj = new JSONObject();
        jsonObj.put(key, value);
        jsonKVArr.put(jsonObj);
     }
 }

The another way is to populate the same in hash map and obtain the same. The other way is to match the requestUri string with regex pattern and obtain the results.

Say for an example to get the value of school I have to match the values between the starting point of the string school and the next & - which doesn't sound good.

1. What is the better approach to parse the query String in java?
2. How could i handle the following thing in a better way?

I need to construct another hash map like the following from the above results like

Map<String, String> resultMap = new HashMap<String, String>;

resultMap.put("empname", name);
resultMap.put("rschool", school);
resultMap.put("empcollege", college);
resultMap.put("favcolor", color);
resultMap.put("favfruit", fruit);

To make it simple all I have to do is to parse the query param and construct a hashMap by naming the key filed differently. How could I do it in a simple way? Any help in this is much appreciated.

Answer 1

Short answer: Every HTTP Client library will do this for you.

Example: Apache HttpClient's URLEncodedUtils class

String queryComponent = "name=raju&school=abcd&college=mnop&color=black&fruit=mango";
List<NameValuePair> params = URLEncodedUtils.parse(queryComponent, Charset.forName("UTF-8"));

They're basically approaching it the same way. Parameter key-value pairs are delimited by & and the keys from the values by = so String's split is appropriate for both.

From what I can tell however your hashmap inserts are mapping new keys to the existing values so there's really no optimization, save maybe for moving to a Java 8 Stream for readability/maintenance and/or discarding the initial jsonArray and mapping straight to the hashmap.

Answer 2

Here is another possible solution:

    Pattern pat = Pattern.compile("([^&=]+)=([^&]*)");
    Matcher matcher = pat.matcher(requestUri);
    Map<String,String> map = new HashMap<>();
    while (matcher.find()) {
        map.put(matcher.group(1), matcher.group(2));
    }
    System.out.println(map);

Answer 3

You can use Java 8 and store your data in HashMap in one operation.

Map<String,String> map = Pattern.compile("\\s*&\\s*")
                .splitAsStream(requestUri.trim())
                .map(s -> s.split("=", 2))
                .collect(Collectors.toMap(a -> a[0], a -> a.length > 1 ? a[1]: ""));

Answer 4

You can do it by Jersey library ( com.sun.jersey.api.uri.UriComponent or org.glassfish.jersey.uri.UriComponent class):

String queryComponent = "name=raju&school=abcd&college=mnop&color=black&fruit=mango";
MultivaluedMap<String, String> params = UriComponent.decodeQuery(queryComponent, true);

Answer 5

Use jackson json parser. Maven dependency:

<dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.5.3</version>
        </dependency>

Now use ObjectMapper to create Map from json string:

ObjectMapper mapper = new ObjectMapper();
Map list = mapper.readValue(requestUri, Map.class);