Gson

Usage

Gson utilizes reflection, meaning that classes do not have to be modified to be serialized or deserialized. By default, a class only needs a defined default (no-args) constructor; however, this requirement can be circumvented (see Features).

The following example demonstrates the basic usage of Gson when serializing a sample object:

<span id="mwGw"></span><span class="kn" id="mwHA">package</span><span class="w" id="mwHQ"> </span><span class="nn" id="mwHg">example</span><span class="p" id="mwHw">;</span> <span class="kd" id="mwIA">public</span><span class="w" id="mwIQ"> </span><span class="kd" id="mwIg">class</span> <span class="nc" id="mwIw">Car</span><span class="w" id="mwJA"> </span><span class="p" id="mwJQ">{</span> <span class="w" id="mwJg"> </span><span class="kd" id="mwJw">public</span><span class="w" id="mwKA"> </span><span class="n" id="mwKQ">String</span><span class="w" id="mwKg"> </span><span class="n" id="mwKw">manufacturer</span><span class="p" id="mwLA">;</span> <span class="w" id="mwLQ"> </span><span class="kd" id="mwLg">public</span><span class="w" id="mwLw"> </span><span class="n" id="mwMA">String</span><span class="w" id="mwMQ"> </span><span class="n" id="mwMg">model</span><span class="p" id="mwMw">;</span> <span class="w" id="mwNA"> </span><span class="kd" id="mwNQ">public</span><span class="w" id="mwNg"> </span><span class="kt" id="mwNw">double</span><span class="w" id="mwOA"> </span><span class="n" id="mwOQ">capacity</span><span class="p" id="mwOg">;</span> <span class="w" id="mwOw"> </span><span class="kd" id="mwPA">public</span><span class="w" id="mwPQ"> </span><span class="kt" id="mwPg">boolean</span><span class="w" id="mwPw"> </span><span class="n" id="mwQA">accident</span><span class="p" id="mwQQ">;</span> <span class="w" id="mwQg"> </span><span class="kd" id="mwQw">public</span><span class="w" id="mwRA"> </span><span class="nf" id="mwRQ">Car</span><span class="p" id="mwRg">()</span><span class="w" id="mwRw"> </span><span class="p" id="mwSA">{</span> <span class="w" id="mwSQ"> </span><span class="p" id="mwSg">}</span> <span class="w" id="mwSw"> </span><span class="kd" id="mwTA">public</span><span class="w" id="mwTQ"> </span><span class="nf" id="mwTg">Car</span><span class="p" id="mwTw">(</span><span class="n" id="mwUA">String</span><span class="w" id="mwUQ"> </span><span class="n" id="mwUg">manufacturer</span><span class="p" id="mwUw">,</span><span class="w" id="mwVA"> </span><span class="n" id="mwVQ">String</span><span class="w" id="mwVg"> </span><span class="n" id="mwVw">model</span><span class="p" id="mwWA">,</span><span class="w" id="mwWQ"> </span><span class="kt" id="mwWg">double</span><span class="w" id="mwWw"> </span><span class="n" id="mwXA">capacity</span><span class="p" id="mwXQ">,</span><span class="w" id="mwXg"> </span><span class="kt" id="mwXw">boolean</span><span class="w" id="mwYA"> </span><span class="n" id="mwYQ">accident</span><span class="p" id="mwYg">)</span><span class="w" id="mwYw"> </span><span class="p" id="mwZA">{</span> <span class="w" id="mwZQ"> </span><span class="k" id="mwZg">this</span><span class="p" id="mwZw">.</span><span class="na" id="mwaA">manufacturer</span><span class="w" id="mwaQ"> </span><span class="o" id="mwag">=</span><span class="w" id="mwaw"> </span><span class="n" id="mwbA">manufacturer</span><span class="p" id="mwbQ">;</span> <span class="w" id="mwbg"> </span><span class="k" id="mwbw">this</span><span class="p" id="mwcA">.</span><span class="na" id="mwcQ">model</span><span class="w" id="mwcg"> </span><span class="o" id="mwcw">=</span><span class="w" id="mwdA"> </span><span class="n" id="mwdQ">model</span><span class="p" id="mwdg">;</span> <span class="w" id="mwdw"> </span><span class="k" id="mweA">this</span><span class="p" id="mweQ">.</span><span class="na" id="mweg">capacity</span><span class="w" id="mwew"> </span><span class="o" id="mwfA">=</span><span class="w" id="mwfQ"> </span><span class="n" id="mwfg">capacity</span><span class="p" id="mwfw">;</span> <span class="w" id="mwgA"> </span><span class="k" id="mwgQ">this</span><span class="p" id="mwgg">.</span><span class="na" id="mwgw">accident</span><span class="w" id="mwhA"> </span><span class="o" id="mwhQ">=</span><span class="w" id="mwhg"> </span><span class="n" id="mwhw">accident</span><span class="p" id="mwiA">;</span> <span class="w" id="mwiQ"> </span><span class="p" id="mwig">}</span> <span class="w" id="mwiw"> </span><span class="nd" id="mwjA">@Override</span> <span class="w" id="mwjQ"> </span><span class="kd" id="mwjg">public</span><span class="w" id="mwjw"> </span><span class="n" id="mwkA">String</span><span class="w" id="mwkQ"> </span><span class="nf" id="mwkg">toString</span><span class="p" id="mwkw">()</span><span class="w" id="mwlA"> </span><span class="p" id="mwlQ">{</span> <span class="w" id="mwlg"> </span><span class="k" id="mwlw">return</span><span class="w" id="mwmA"> </span><span class="p" id="mwmQ">(</span><span class="s" id="mwmg">"Manufacturer: "</span><span class="w" id="mwmw"> </span><span class="o" id="mwnA">+</span><span class="w" id="mwnQ"> </span><span class="n" id="mwng">manufacturer</span><span class="w" id="mwnw"> </span><span class="o" id="mwoA">+</span><span class="w" id="mwoQ"> </span><span class="s" id="mwog">", "</span><span class="w" id="mwow"> </span><span class="o" id="mwpA">+</span><span class="w" id="mwpQ"> </span><span class="s" id="mwpg">"Model: "</span><span class="w" id="mwpw"> </span><span class="o" id="mwqA">+</span><span class="w" id="mwqQ"> </span><span class="n" id="mwqg">model</span><span class="w" id="mwqw"> </span><span class="o" id="mwrA">+</span><span class="w" id="mwrQ"> </span><span class="s" id="mwrg">", "</span><span class="w" id="mwrw"> </span><span class="o" id="mwsA">+</span><span class="w" id="mwsQ"> </span><span class="s" id="mwsg">"Capacity: "</span><span class="w" id="mwsw"> </span><span class="o" id="mwtA">+</span><span class="w" id="mwtQ"> </span><span class="n" id="mwtg">capacity</span><span class="w" id="mwtw"> </span><span class="o" id="mwuA">+</span><span class="w" id="mwuQ"> </span><span class="s" id="mwug">", "</span><span class="w" id="mwuw"> </span><span class="o" id="mwvA">+</span><span class="w" id="mwvQ"> </span><span class="s" id="mwvg">"Accident: "</span><span class="w" id="mwvw"> </span><span class="o" id="mwwA">+</span><span class="w" id="mwwQ"> </span><span class="n" id="mwwg">accident</span><span class="p" id="mwww">);</span> <span class="w" id="mwxA"> </span><span class="p" id="mwxQ">}</span> <span class="p" id="mwxg">}</span>

<span id="mwyQ"></span><span class="kn" id="mwyg">package</span><span class="w" id="mwyw"> </span><span class="nn" id="mwzA">example</span><span class="p" id="mwzQ">;</span> <span class="kd" id="mwzg">public</span><span class="w" id="mwzw"> </span><span class="kd" id="mw0A">class</span> <span class="nc" id="mw0Q">Person</span><span class="w" id="mw0g"> </span><span class="p" id="mw0w">{</span> <span class="w" id="mw1A"> </span><span class="kd" id="mw1Q">public</span><span class="w" id="mw1g"> </span><span class="n" id="mw1w">String</span><span class="w" id="mw2A"> </span><span class="n" id="mw2Q">name</span><span class="p" id="mw2g">;</span> <span class="w" id="mw2w"> </span><span class="kd" id="mw3A">public</span><span class="w" id="mw3Q"> </span><span class="n" id="mw3g">String</span><span class="w" id="mw3w"> </span><span class="n" id="mw4A">surname</span><span class="p" id="mw4Q">;</span> <span class="w" id="mw4g"> </span><span class="kd" id="mw4w">public</span><span class="w" id="mw5A"> </span><span class="n" id="mw5Q">Car</span><span class="o" id="mw5g">[]</span><span class="w" id="mw5w"> </span><span class="n" id="mw6A">cars</span><span class="p" id="mw6Q">;</span> <span class="w" id="mw6g"> </span><span class="kd" id="mw6w">public</span><span class="w" id="mw7A"> </span><span class="kt" id="mw7Q">int</span><span class="w" id="mw7g"> </span><span class="n" id="mw7w">phone</span><span class="p" id="mw8A">;</span> <span class="w" id="mw8Q"> </span><span class="kd" id="mw8g">public</span><span class="w" id="mw8w"> </span><span class="kd" id="mw9A">transient</span><span class="w" id="mw9Q"> </span><span class="kt" id="mw9g">int</span><span class="w" id="mw9w"> </span><span class="n" id="mw-A">age</span><span class="p" id="mw-Q">;</span> <span class="w" id="mw-g"> </span><span class="kd" id="mw-w">public</span><span class="w" id="mw_A"> </span><span class="nf" id="mw_Q">Person</span><span class="p" id="mw_g">()</span><span class="w" id="mw_w"> </span><span class="p" id="mwAQA">{</span> <span class="w" id="mwAQE"> </span><span class="p" id="mwAQI">}</span> <span class="w" id="mwAQM"> </span><span class="kd" id="mwAQQ">public</span><span class="w" id="mwAQU"> </span><span class="nf" id="mwAQY">Person</span><span class="p" id="mwAQc">(</span><span class="n" id="mwAQg">String</span><span class="w" id="mwAQk"> </span><span class="n" id="mwAQo">name</span><span class="p" id="mwAQs">,</span><span class="w" id="mwAQw"> </span><span class="n" id="mwAQ0">String</span><span class="w" id="mwAQ4"> </span><span class="n" id="mwAQ8">surname</span><span class="p" id="mwARA">,</span><span class="w" id="mwARE"> </span><span class="kt" id="mwARI">int</span><span class="w" id="mwARM"> </span><span class="n" id="mwARQ">phone</span><span class="p" id="mwARU">,</span><span class="w" id="mwARY"> </span><span class="kt" id="mwARc">int</span><span class="w" id="mwARg"> </span><span class="n" id="mwARk">age</span><span class="p" id="mwARo">,</span><span class="w" id="mwARs"> </span><span class="n" id="mwARw">Car</span><span class="o" id="mwAR0">[]</span><span class="w" id="mwAR4"> </span><span class="n" id="mwAR8">cars</span><span class="p" id="mwASA">)</span><span class="w" id="mwASE"> </span><span class="p" id="mwASI">{</span> <span class="w" id="mwASM"> </span><span class="k" id="mwASQ">this</span><span class="p" id="mwASU">.</span><span class="na" id="mwASY">name</span><span class="w" id="mwASc"> </span><span class="o" id="mwASg">=</span><span class="w" id="mwASk"> </span><span class="n" id="mwASo">name</span><span class="p" id="mwASs">;</span> <span class="w" id="mwASw"> </span><span class="k" id="mwAS0">this</span><span class="p" id="mwAS4">.</span><span class="na" id="mwAS8">surname</span><span class="w" id="mwATA"> </span><span class="o" id="mwATE">=</span><span class="w" id="mwATI"> </span><span class="n" id="mwATM">surname</span><span class="p" id="mwATQ">;</span> <span class="w" id="mwATU"> </span><span class="k" id="mwATY">this</span><span class="p" id="mwATc">.</span><span class="na" id="mwATg">cars</span><span class="w" id="mwATk"> </span><span class="o" id="mwATo">=</span><span class="w" id="mwATs"> </span><span class="n" id="mwATw">cars</span><span class="p" id="mwAT0">;</span> <span class="w" id="mwAT4"> </span><span class="k" id="mwAT8">this</span><span class="p" id="mwAUA">.</span><span class="na" id="mwAUE">phone</span><span class="w" id="mwAUI"> </span><span class="o" id="mwAUM">=</span><span class="w" id="mwAUQ"> </span><span class="n" id="mwAUU">phone</span><span class="p" id="mwAUY">;</span> <span class="w" id="mwAUc"> </span><span class="k" id="mwAUg">this</span><span class="p" id="mwAUk">.</span><span class="na" id="mwAUo">age</span><span class="w" id="mwAUs"> </span><span class="o" id="mwAUw">=</span><span class="w" id="mwAU0"> </span><span class="n" id="mwAU4">age</span><span class="p" id="mwAU8">;</span> <span class="w" id="mwAVA"> </span><span class="p" id="mwAVE">}</span> <span class="w" id="mwAVI"> </span><span class="nd" id="mwAVM">@Override</span> <span class="w" id="mwAVQ"> </span><span class="kd" id="mwAVU">public</span><span class="w" id="mwAVY"> </span><span class="n" id="mwAVc">String</span><span class="w" id="mwAVg"> </span><span class="nf" id="mwAVk">toString</span><span class="p" id="mwAVo">()</span><span class="w" id="mwAVs"> </span><span class="p" id="mwAVw">{</span> <span class="w" id="mwAV0"> </span><span class="n" id="mwAV4">StringBuilder</span><span class="w" id="mwAV8"> </span><span class="n" id="mwAWA">sb</span><span class="w" id="mwAWE"> </span><span class="o" id="mwAWI">=</span><span class="w" id="mwAWM"> </span><span class="k" id="mwAWQ">new</span><span class="w" id="mwAWU"> </span><span class="n" id="mwAWY">StringBuilder</span><span class="p" id="mwAWc">();</span> <span class="w" id="mwAWg"> </span><span class="n" id="mwAWk">sb</span><span class="p" id="mwAWo">.</span><span class="na" id="mwAWs">append</span><span class="p" id="mwAWw">(</span><span class="s" id="mwAW0">"Name: "</span><span class="p" id="mwAW4">).</span><span class="na" id="mwAW8">append</span><span class="p" id="mwAXA">(</span><span class="n" id="mwAXE">name</span><span class="p" id="mwAXI">).</span><span class="na" id="mwAXM">append</span><span class="p" id="mwAXQ">(</span><span class="s" id="mwAXU">" "</span><span class="p" id="mwAXY">).</span><span class="na" id="mwAXc">append</span><span class="p" id="mwAXg">(</span><span class="n" id="mwAXk">surname</span><span class="p" id="mwAXo">).</span><span class="na" id="mwAXs">append</span><span class="p" id="mwAXw">(</span><span class="s" id="mwAX0">"\n"</span><span class="p" id="mwAX4">);</span> <span class="w" id="mwAX8"> </span><span class="n" id="mwAYA">sb</span><span class="p" id="mwAYE">.</span><span class="na" id="mwAYI">append</span><span class="p" id="mwAYM">(</span><span class="s" id="mwAYQ">"Phone: "</span><span class="p" id="mwAYU">).</span><span class="na" id="mwAYY">append</span><span class="p" id="mwAYc">(</span><span class="n" id="mwAYg">phone</span><span class="p" id="mwAYk">).</span><span class="na" id="mwAYo">append</span><span class="p" id="mwAYs">(</span><span class="s" id="mwAYw">"\n"</span><span class="p" id="mwAY0">);</span> <span class="w" id="mwAY4"> </span><span class="n" id="mwAY8">sb</span><span class="p" id="mwAZA">.</span><span class="na" id="mwAZE">append</span><span class="p" id="mwAZI">(</span><span class="s" id="mwAZM">"Age: "</span><span class="p" id="mwAZQ">).</span><span class="na" id="mwAZU">append</span><span class="p" id="mwAZY">(</span><span class="n" id="mwAZc">age</span><span class="p" id="mwAZg">).</span><span class="na" id="mwAZk">append</span><span class="p" id="mwAZo">(</span><span class="s" id="mwAZs">"\n"</span><span class="p" id="mwAZw">);</span> <span class="w" id="mwAZ0"> </span><span class="kt" id="mwAZ4">int</span><span class="w" id="mwAZ8"> </span><span class="n" id="mwAaA">i</span><span class="w" id="mwAaE"> </span><span class="o" id="mwAaI">=</span><span class="w" id="mwAaM"> </span><span class="mi" id="mwAaQ">0</span><span class="p" id="mwAaU">;</span> <span class="w" id="mwAaY"> </span><span class="k" id="mwAac">for</span><span class="w" id="mwAag"> </span><span class="p" id="mwAak">(</span><span class="n" id="mwAao">Car</span><span class="w" id="mwAas"> </span><span class="n" id="mwAaw">car</span><span class="w" id="mwAa0"> </span><span class="p" id="mwAa4">:</span><span class="w" id="mwAa8"> </span><span class="n" id="mwAbA">cars</span><span class="p" id="mwAbE">)</span><span class="w" id="mwAbI"> </span><span class="p" id="mwAbM">{</span> <span class="w" id="mwAbQ"> </span><span class="n" id="mwAbU">i</span><span class="o" id="mwAbY">++</span><span class="p" id="mwAbc">;</span> <span class="w" id="mwAbg"> </span><span class="n" id="mwAbk">sb</span><span class="p" id="mwAbo">.</span><span class="na" id="mwAbs">append</span><span class="p" id="mwAbw">(</span><span class="s" id="mwAb0">"Car "</span><span class="p" id="mwAb4">).</span><span class="na" id="mwAb8">append</span><span class="p" id="mwAcA">(</span><span class="n" id="mwAcE">i</span><span class="p" id="mwAcI">).</span><span class="na" id="mwAcM">append</span><span class="p" id="mwAcQ">(</span><span class="s" id="mwAcU">": "</span><span class="p" id="mwAcY">).</span><span class="na" id="mwAcc">append</span><span class="p" id="mwAcg">(</span><span class="n" id="mwAck">car</span><span class="p" id="mwAco">).</span><span class="na" id="mwAcs">append</span><span class="p" id="mwAcw">(</span><span class="s" id="mwAc0">"\n"</span><span class="p" id="mwAc4">);</span> <span class="w" id="mwAc8"> </span><span class="p" id="mwAdA">}</span> <span class="w" id="mwAdE"> </span><span class="k" id="mwAdI">return</span><span class="w" id="mwAdM"> </span><span class="n" id="mwAdQ">sb</span><span class="p" id="mwAdU">.</span><span class="na" id="mwAdY">toString</span><span class="p" id="mwAdc">();</span> <span class="w" id="mwAdg"> </span><span class="p" id="mwAdk">}</span> <span class="p" id="mwAdo">}</span>

<span id="mwAd0"></span><span class="kn" id="mwAd4">package</span><span class="w" id="mwAd8"> </span><span class="nn" id="mwAeA">main</span><span class="p" id="mwAeE">;</span> <span class="kn" id="mwAeI">import</span><span class="w" id="mwAeM"> </span><span class="nn" id="mwAeQ">example.Car</span><span class="p" id="mwAeU">;</span> <span class="kn" id="mwAeY">import</span><span class="w" id="mwAec"> </span><span class="nn" id="mwAeg">example.Person</span><span class="p" id="mwAek">;</span> <span class="kn" id="mwAeo">import</span><span class="w" id="mwAes"> </span><span class="nn" id="mwAew">com.google.gson.Gson</span><span class="p" id="mwAe0">;</span> <span class="kn" id="mwAe4">import</span><span class="w" id="mwAe8"> </span><span class="nn" id="mwAfA">com.google.gson.GsonBuilder</span><span class="p" id="mwAfE">;</span> <span class="kd" id="mwAfI">public</span><span class="w" id="mwAfM"> </span><span class="kd" id="mwAfQ">class</span> <span class="nc" id="mwAfU">Main</span><span class="w" id="mwAfY"> </span><span class="p" id="mwAfc">{</span> <span class="w" id="mwAfg"> </span><span class="kd" id="mwAfk">public</span><span class="w" id="mwAfo"> </span><span class="kd" id="mwAfs">static</span><span class="w" id="mwAfw"> </span><span class="kt" id="mwAf0">void</span><span class="w" id="mwAf4"> </span><span class="nf" id="mwAf8">main</span><span class="p" id="mwAgA">(</span><span class="n" id="mwAgE">String</span><span class="o" id="mwAgI">[]</span><span class="w" id="mwAgM"> </span><span class="n" id="mwAgQ">args</span><span class="p" id="mwAgU">)</span><span class="w" id="mwAgY"> </span><span class="p" id="mwAgc">{</span> <span class="w" id="mwAgg"> </span><span class="c1" id="mwAgk">// Enable pretty printing for demonstration purposes</span> <span class="w" id="mwAgo"> </span><span class="c1" id="mwAgs">// Can also directly create instance with `new Gson()`; this will produce compact JSON</span> <span class="w" id="mwAgw"> </span><span class="n" id="mwAg0">Gson</span><span class="w" id="mwAg4"> </span><span class="n" id="mwAg8">gson</span><span class="w" id="mwAhA"> </span><span class="o" id="mwAhE">=</span><span class="w" id="mwAhI"> </span><span class="k" id="mwAhM">new</span><span class="w" id="mwAhQ"> </span><span class="n" id="mwAhU">GsonBuilder</span><span class="p" id="mwAhY">().</span><span class="na" id="mwAhc">setPrettyPrinting</span><span class="p" id="mwAhg">().</span><span class="na" id="mwAhk">create</span><span class="p" id="mwAho">();</span> <span class="w" id="mwAhs"> </span><span class="n" id="mwAhw">Car</span><span class="w" id="mwAh0"> </span><span class="n" id="mwAh4">audi</span><span class="w" id="mwAh8"> </span><span class="o" id="mwAiA">=</span><span class="w" id="mwAiE"> </span><span class="k" id="mwAiI">new</span><span class="w" id="mwAiM"> </span><span class="n" id="mwAiQ">Car</span><span class="p" id="mwAiU">(</span><span class="s" id="mwAiY">"Audi"</span><span class="p" id="mwAic">,</span><span class="w" id="mwAig"> </span><span class="s" id="mwAik">"A4"</span><span class="p" id="mwAio">,</span><span class="w" id="mwAis"> </span><span class="mf" id="mwAiw">1.8</span><span class="p" id="mwAi0">,</span><span class="w" id="mwAi4"> </span><span class="kc" id="mwAi8">false</span><span class="p" id="mwAjA">);</span> <span class="w" id="mwAjE"> </span><span class="n" id="mwAjI">Car</span><span class="w" id="mwAjM"> </span><span class="n" id="mwAjQ">skoda</span><span class="w" id="mwAjU"> </span><span class="o" id="mwAjY">=</span><span class="w" id="mwAjc"> </span><span class="k" id="mwAjg">new</span><span class="w" id="mwAjk"> </span><span class="n" id="mwAjo">Car</span><span class="p" id="mwAjs">(</span><span class="s" id="mwAjw">"Škoda"</span><span class="p" id="mwAj0">,</span><span class="w" id="mwAj4"> </span><span class="s" id="mwAj8">"Octavia"</span><span class="p" id="mwAkA">,</span><span class="w" id="mwAkE"> </span><span class="mf" id="mwAkI">2.0</span><span class="p" id="mwAkM">,</span><span class="w" id="mwAkQ"> </span><span class="kc" id="mwAkU">true</span><span class="p" id="mwAkY">);</span> <span class="w" id="mwAkc"> </span><span class="n" id="mwAkg">Car</span><span class="o" id="mwAkk">[]</span><span class="w" id="mwAko"> </span><span class="n" id="mwAks">cars</span><span class="w" id="mwAkw"> </span><span class="o" id="mwAk0">=</span><span class="w" id="mwAk4"> </span><span class="p" id="mwAk8">{</span><span class="n" id="mwAlA">audi</span><span class="p" id="mwAlE">,</span><span class="w" id="mwAlI"> </span><span class="n" id="mwAlM">skoda</span><span class="p" id="mwAlQ">};</span> <span class="w" id="mwAlU"> </span><span class="n" id="mwAlY">Person</span><span class="w" id="mwAlc"> </span><span class="n" id="mwAlg">johnDoe</span><span class="w" id="mwAlk"> </span><span class="o" id="mwAlo">=</span><span class="w" id="mwAls"> </span><span class="k" id="mwAlw">new</span><span class="w" id="mwAl0"> </span><span class="n" id="mwAl4">Person</span><span class="p" id="mwAl8">(</span><span class="s" id="mwAmA">"John"</span><span class="p" id="mwAmE">,</span><span class="w" id="mwAmI"> </span><span class="s" id="mwAmM">"Doe"</span><span class="p" id="mwAmQ">,</span><span class="w" id="mwAmU"> </span><span class="mi" id="mwAmY">2025550191</span><span class="p" id="mwAmc">,</span><span class="w" id="mwAmg"> </span><span class="mi" id="mwAmk">35</span><span class="p" id="mwAmo">,</span><span class="w" id="mwAms"> </span><span class="n" id="mwAmw">cars</span><span class="p" id="mwAm0">);</span> <span class="w" id="mwAm4"> </span><span class="n" id="mwAm8">System</span><span class="p" id="mwAnA">.</span><span class="na" id="mwAnE">out</span><span class="p" id="mwAnI">.</span><span class="na" id="mwAnM">println</span><span class="p" id="mwAnQ">(</span><span class="n" id="mwAnU">gson</span><span class="p" id="mwAnY">.</span><span class="na" id="mwAnc">toJson</span><span class="p" id="mwAng">(</span><span class="n" id="mwAnk">johnDoe</span><span class="p" id="mwAno">));</span> <span class="w" id="mwAns"> </span><span class="p" id="mwAnw">}</span> <span class="p" id="mwAn0">}</span>

Calling the code of the above Main class will result in the following JSON output:

<span id="mwAoI"></span><span class="p" id="mwAoM">{</span> <span class="w" id="mwAoQ"> </span><span class="nt" id="mwAoU">"name"</span><span class="p" id="mwAoY">:</span><span class="w" id="mwAoc"> </span><span class="s2" id="mwAog">"John"</span><span class="p" id="mwAok">,</span> <span class="w" id="mwAoo"> </span><span class="nt" id="mwAos">"surname"</span><span class="p" id="mwAow">:</span><span class="w" id="mwAo0"> </span><span class="s2" id="mwAo4">"Doe"</span><span class="p" id="mwAo8">,</span> <span class="w" id="mwApA"> </span><span class="nt" id="mwApE">"cars"</span><span class="p" id="mwApI">:</span><span class="w" id="mwApM"> </span><span class="p" id="mwApQ">[</span> <span class="w" id="mwApU"> </span><span class="p" id="mwApY">{</span> <span class="w" id="mwApc"> </span><span class="nt" id="mwApg">"manufacturer"</span><span class="p" id="mwApk">:</span><span class="w" id="mwApo"> </span><span class="s2" id="mwAps">"Audi"</span><span class="p" id="mwApw">,</span> <span class="w" id="mwAp0"> </span><span class="nt" id="mwAp4">"model"</span><span class="p" id="mwAp8">:</span><span class="w" id="mwAqA"> </span><span class="s2" id="mwAqE">"A4"</span><span class="p" id="mwAqI">,</span> <span class="w" id="mwAqM"> </span><span class="nt" id="mwAqQ">"capacity"</span><span class="p" id="mwAqU">:</span><span class="w" id="mwAqY"> </span><span class="mf" id="mwAqc">1.8</span><span class="p" id="mwAqg">,</span> <span class="w" id="mwAqk"> </span><span class="nt" id="mwAqo">"accident"</span><span class="p" id="mwAqs">:</span><span class="w" id="mwAqw"> </span><span class="kc" id="mwAq0">false</span> <span class="w" id="mwAq4"> </span><span class="p" id="mwAq8">},</span> <span class="w" id="mwArA"> </span><span class="p" id="mwArE">{</span> <span class="w" id="mwArI"> </span><span class="nt" id="mwArM">"manufacturer"</span><span class="p" id="mwArQ">:</span><span class="w" id="mwArU"> </span><span class="s2" id="mwArY">"Škoda"</span><span class="p" id="mwArc">,</span> <span class="w" id="mwArg"> </span><span class="nt" id="mwArk">"model"</span><span class="p" id="mwAro">:</span><span class="w" id="mwArs"> </span><span class="s2" id="mwArw">"Octavia"</span><span class="p" id="mwAr0">,</span> <span class="w" id="mwAr4"> </span><span class="nt" id="mwAr8">"capacity"</span><span class="p" id="mwAsA">:</span><span class="w" id="mwAsE"> </span><span class="mf" id="mwAsI">2.0</span><span class="p" id="mwAsM">,</span> <span class="w" id="mwAsQ"> </span><span class="nt" id="mwAsU">"accident"</span><span class="p" id="mwAsY">:</span><span class="w" id="mwAsc"> </span><span class="kc" id="mwAsg">true</span> <span class="w" id="mwAsk"> </span><span class="p" id="mwAso">}</span> <span class="w" id="mwAss"> </span><span class="p" id="mwAsw">],</span> <span class="w" id="mwAs0"> </span><span class="nt" id="mwAs4">"phone"</span><span class="p" id="mwAs8">:</span><span class="w" id="mwAtA"> </span><span class="mi" id="mwAtE">2025550191</span> <span class="p" id="mwAtI">}</span>

Since the Person's field age is marked as transient, it is not included in the output.

<span id="mwAtw"></span><span class="kn" id="mwAt0">package</span><span class="w" id="mwAt4"> </span><span class="nn" id="mwAt8">main</span><span class="p" id="mwAuA">;</span> <span class="kn" id="mwAuE">import</span><span class="w" id="mwAuI"> </span><span class="nn" id="mwAuM">example.Person</span><span class="p" id="mwAuQ">;</span> <span class="kn" id="mwAuU">import</span><span class="w" id="mwAuY"> </span><span class="nn" id="mwAuc">com.google.gson.Gson</span><span class="p" id="mwAug">;</span> <span class="kd" id="mwAuk">public</span><span class="w" id="mwAuo"> </span><span class="kd" id="mwAus">class</span> <span class="nc" id="mwAuw">Main</span><span class="w" id="mwAu0"> </span><span class="p" id="mwAu4">{</span> <span class="w" id="mwAu8"> </span><span class="kd" id="mwAvA">public</span><span class="w" id="mwAvE"> </span><span class="kd" id="mwAvI">static</span><span class="w" id="mwAvM"> </span><span class="kt" id="mwAvQ">void</span><span class="w" id="mwAvU"> </span><span class="nf" id="mwAvY">main</span><span class="p" id="mwAvc">(</span><span class="n" id="mwAvg">String</span><span class="o" id="mwAvk">[]</span><span class="w" id="mwAvo"> </span><span class="n" id="mwAvs">args</span><span class="p" id="mwAvw">)</span><span class="w" id="mwAv0"> </span><span class="p" id="mwAv4">{</span> <span class="w" id="mwAv8"> </span><span class="n" id="mwAwA">Gson</span><span class="w" id="mwAwE"> </span><span class="n" id="mwAwI">gson</span><span class="w" id="mwAwM"> </span><span class="o" id="mwAwQ">=</span><span class="w" id="mwAwU"> </span><span class="k" id="mwAwY">new</span><span class="w" id="mwAwc"> </span><span class="n" id="mwAwg">Gson</span><span class="p" id="mwAwk">();</span> <span class="w" id="mwAwo"> </span><span class="n" id="mwAws">String</span><span class="w" id="mwAww"> </span><span class="n" id="mwAw0">json</span><span class="w" id="mwAw4"> </span><span class="o" id="mwAw8">=</span><span class="w" id="mwAxA"> </span><span class="s" id="mwAxE">"{\"name\":\"John\",\"surname\":\"Doe\",\"cars\":[{\"manufacturer\":\"Audi\",\"model\":\"A4\","</span><span class="w" id="mwAxI"> </span><span class="o" id="mwAxM">+</span> <span class="w" id="mwAxQ"> </span><span class="s" id="mwAxU">"\"capacity\":1.8,\"accident\":false},{\"manufacturer\":\"Škoda\",\"model\":\"Octavia\",\"capacity\""</span><span class="w" id="mwAxY"> </span><span class="o" id="mwAxc">+</span> <span class="w" id="mwAxg"> </span><span class="s" id="mwAxk">":2.0,\"accident\":true}],\"phone\":2025550191}"</span><span class="p" id="mwAxo">;</span> <span class="w" id="mwAxs"> </span><span class="n" id="mwAxw">Person</span><span class="w" id="mwAx0"> </span><span class="n" id="mwAx4">johnDoe</span><span class="w" id="mwAx8"> </span><span class="o" id="mwAyA">=</span><span class="w" id="mwAyE"> </span><span class="n" id="mwAyI">gson</span><span class="p" id="mwAyM">.</span><span class="na" id="mwAyQ">fromJson</span><span class="p" id="mwAyU">(</span><span class="n" id="mwAyY">json</span><span class="p" id="mwAyc">,</span><span class="w" id="mwAyg"> </span><span class="n" id="mwAyk">Person</span><span class="p" id="mwAyo">.</span><span class="na" id="mwAys">class</span><span class="p" id="mwAyw">);</span> <span class="w" id="mwAy0"> </span><span class="n" id="mwAy4">System</span><span class="p" id="mwAy8">.</span><span class="na" id="mwAzA">out</span><span class="p" id="mwAzE">.</span><span class="na" id="mwAzI">println</span><span class="p" id="mwAzM">(</span><span class="n" id="mwAzQ">johnDoe</span><span class="p" id="mwAzU">.</span><span class="na" id="mwAzY">toString</span><span class="p" id="mwAzc">());</span> <span class="w" id="mwAzg"> </span><span class="p" id="mwAzk">}</span> <span class="p" id="mwAzo">}</span>

To deserialize the output produced by the last example, you can execute the code above, which generates the following output:

<span id="mwAz4"></span><span class="go" id="mwAz8">Name: John Doe</span> <span class="go" id="mwA0A">Phone: 2025550191</span> <span class="go" id="mwA0E">Age: 0</span> <span class="go" id="mwA0I">Car 1: Manufacturer: Audi, Model: A4, Capacity: 1.8, Accident: false</span> <span class="go" id="mwA0M">Car 2: Manufacturer: Škoda, Model: Octavia, Capacity: 2.0, Accident: true</span>

This shows how Gson can be used with the Java Platform Module System for the example above:

<span id="mwA0g"></span><span class="n" id="mwA0k">module</span><span class="w" id="mwA0o"> </span><span class="n" id="mwA0s">GsonExample</span><span class="w" id="mwA0w"> </span><span class="p" id="mwA00">{</span> <span class="w" id="mwA04"> </span><span class="n" id="mwA08">requires</span><span class="w" id="mwA1A"> </span><span class="n" id="mwA1E">com</span><span class="p" id="mwA1I">.</span><span class="na" id="mwA1M">google</span><span class="p" id="mwA1Q">.</span><span class="na" id="mwA1U">gson</span><span class="p" id="mwA1Y">;</span> <span class="w" id="mwA1c"> </span><span class="c1" id="mwA1g">// Open package declared in the example above to allow Gson to use reflection on classes</span> <span class="w" id="mwA1k"> </span><span class="c1" id="mwA1o">// inside the package (and also access non-public fields)</span> <span class="w" id="mwA1s"> </span><span class="n" id="mwA1w">opens</span><span class="w" id="mwA10"> </span><span class="n" id="mwA14">example</span><span class="w" id="mwA18"> </span><span class="n" id="mwA2A">to</span><span class="w" id="mwA2E"> </span><span class="n" id="mwA2I">com</span><span class="p" id="mwA2M">.</span><span class="na" id="mwA2Q">google</span><span class="p" id="mwA2U">.</span><span class="na" id="mwA2Y">gson</span><span class="p" id="mwA2c">;</span> <span class="p" id="mwA2g">}</span>

For more extensive examples, see Gson's usage guide on their GitHub repository.

Features

• Gson can handle collections, generic types, and nested classes (including inner classes, which cannot be done by default).
• When deserializing, Gson navigates the type tree of the object being deserialized, which means that it ignores extra fields present in the JSON input.
• The user can:
  • write a custom serializer and/or deserializer so that they can control the whole process, and even deserialize instances of classes for which the source code is inaccessible.
  • write an InstanceCreator, which allows them to deserialize instances of classes without a defined no-args constructor.
• Gson is highly customizable, as you can specify:

• Compact/pretty printing (whether you want compact or readable output)
• How to handle null object fields – by default they are not present in the output
• Excluding fields - rules of what fields are intended to be excluded from deserialization
• How to convert Java field names