如何在Gson中逃脱斜线

Question

According to the json specs, escaping " / " is optional.

Gson does not do it by default, but I am dealing with a webservice which is expecting escaped " / ". So what I want to send is " somestring\\\\/someotherstring ". Any ideas on how to achieve this?

To make things clearer: if I try to deserialize " \\\\/ " with Gson, it will send " \\\\\\\\/ ", which is not what I want!

Answer 1

Answer: The Custom Serializer

You can write your own Custom Serializer - I have created one which follows the rule that you want / to be \\\\/ but if the string is already escaped you want it to stay \\\\/ and not be \\\\\\\\/ .

package com.dominikangerer.q29396608;

import java.lang.reflect.Type;

import com.google.gson.JsonElement;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

public class EscapeStringSerializer implements JsonSerializer<String> {

    @Override
    public JsonElement serialize(String src, Type typeOfSrc,
            JsonSerializationContext context) {
        src = createEscapedString(src);
        return new JsonPrimitive(src);
    }

    private String createEscapedString(String src) {
        // StringBuilder for the new String
        StringBuilder builder = new StringBuilder();

        // First occurrence
        int index = src.indexOf('/');
        // lastAdded starting at position 0
        int lastAdded = 0;

        while (index >= 0) {
            // append first part without a /
            builder.append(src.substring(lastAdded, index));

            // if / doesn't have a \ directly in front - add a \
            if (index - 1 >= 0 && !src.substring(index - 1, index).equals("\\")) {
                builder.append("\\");
                // if we are at index 0 we also add it because - well it's the
                // first character
            } else if (index == 0) {
                builder.append("\\");
            }

            // change last added to index
            lastAdded = index;
            // change index to the new occurrence of the /
            index = src.indexOf('/', index + 1);
        }

        // add the rest of the string
        builder.append(src.substring(lastAdded, src.length()));
        // return the new String
        return builder.toString();
    }
}

This will create from the following String:

"12 /first /second \\/third\\/fourth\\//fifth"`

the output:

"12 \\/first \\/second \\/third\\/fourth\\/\\/fifth"

Register your Custom Serializer

Than of course you need to pass this serializer to Gson on Setup like this:

Gson gson = new GsonBuilder().registerTypeAdapter(String.class, new EscapeStringSerializer()).create();
String json = gson.toJson(yourObject);

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Downloadable & executable Example

You can find this answer and the exact example in my github stackoverflow answers repo:

Gson CustomSerializer to escape a String in a special way by DominikAngerer

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See also

• Gson User Guide - Custom serializers and deserializers