实现的业务逻辑是这样的：
通过http请求，返回一个json格式的数据，然后将json数据转化为java对象返回给调用方。
Http采用OkHttp库，json转化采用jackson库。
一.简介
1）okhttpclient
OkHttpClient官网： http://square.github.io/okhttp/
OkHttp GitHub地址：https://github.com/square/okhttp
最常用的是两个http请求是get和post，我下面的代码就只用到这两个请求。
Maven依赖：
<dependency>
<groupId>com.squareup.okhttp3</groupId>
<artifactId>okhttp</artifactId>
<version>3.6.0</version>
</dependency>
2）jackson
Jackson的文档：http://wiki.fasterxml.com/JacksonInFiveMinutes
Jackson的maven依赖
<dependency>
<groupId>com.fasterxml.jackson</groupId>
<artifactId>jackson-parent</artifactId>
<version>2.8</version>
</dependency>
由于采用了javabean的方式，所以json和java类的互转变得简单。

二．代码
java类：

public  class Transaction {
　　//使用了静态的内部类
    public static class Output{
        String address;
        long amount;

        public String getAddress() {
            return address;
        }

        public long getAmount() {
            return amount;
        }

        public void setAddress(String address) {
            this.address = address;
        }

        public void setAmount(long amount) {
            this.amount = amount;
        }

        @Override
        public String toString() {
            return "Output{" +
                    "address=‘" + address + ‘\‘‘ +
                    ", amount=" + amount +
                    ‘}‘;
        }
    }

    private String txid;
    private String action;
    private long amount;
    private long fees;
    private long time;
    private int confirmations;
    private List<Output> outputs;

    public void setTxid(String txid) {
        this.txid = txid;
    }

    public void setAction(String action) {
        this.action = action;
    }

    public void setAmount(long amount) {
        this.amount = amount;
    }

    public void setFees(long fees) {
        this.fees = fees;
    }

    public void setTime(long time) {
        this.time = time;
    }

    public void setConfirmations(int confirmations) {
        this.confirmations = confirmations;
    }

    public String getTxid() {
        return txid;
    }

    public void setOutputs(List<Output> outputs) {
        this.outputs = outputs;
    }

    @Override
    public String toString() {
        return "Transaction{" +
                "txid=‘" + txid + ‘\‘‘ +
                ", action=‘" + action + ‘\‘‘ +
                ", amount=" + amount +
                ", fees=" + fees +
                ", time=" + time +
                ", confirmations=" + confirmations +
                ", outputs=" + outputs +
                ‘}‘;
    }
}

http请求：

public class HttpClient {
    public static final MediaType JSON = MediaType.parse("application/json;charset=utf-8");

    public static String httpGet(String url) throws IOException {
        OkHttpClient httpClient = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .build();
        Response response = httpClient.newCall(request).execute();
        return response.body().string(); // 返回的是string 类型，json的mapper可以直接处理
    }

    public static String httpPost(String url, String json) throws IOException {
        OkHttpClient httpClient = new OkHttpClient();
        RequestBody requestBody = RequestBody.create(JSON, json);
        Request request = new Request.Builder()
                .url(url)
                .post(requestBody)
                .build();
        Response response = httpClient.newCall(request).execute();
        return response.body().string();
    }
｝

json转化：

public Transaction[] getTransaction(int skip,int limit){
    String txHistoryUrl = String.format("%s%s?skip=%d&limit=%d",url,TX_HISTORY,skip,limit); //url 后边的参数是业务规定，格式可以参考，具体可以自定义
    System.out.println(txHistoryUrl);
    try{
        String newTx = HttpClient.httpGet(txHistoryUrl);
        System.out.println(newTx);
        ObjectMapper mapper = new ObjectMapper(); // 只需要一个mapper就可以实现
        return mapper.readValue(newTx,Transaction[].class);
    }catch (IOException e){
        e.printStackTrace();
    }
    return null;
}
json数据如下：
[{"txid":"ad416e1b4b8b807b4a0946affb17cf253c1af7a7e6c6a9e21fac2e93b2c88746","action":"received","amount":10000,"fees":3800,"time":1486111663,"confirmations":179,"outputs":[{"amount":10000,"address":"2MxDyD4idPv8LqYNP4Aq4QExRhTckqNK8zK"}]},{"txid":"2dadf7b391935af15f5f70e775ed5d7a03d629db4bdde1cd93e31b8311db4949","action":"received","amount":1000000,"fees":4416,"time":1485241194,"confirmations":1721,"outputs":[{"amount":1000000,"address":"2MxDyD4idPv8LqYNP4Aq4QExRhTckqNK8zK"}]}]

三．问题解决
Json错误：Can not deserialize instance of xx out of START_ARRAY token
Server
这个可能是后台返回的是数组类型的json，所以transaction要用数组
return mapper.readValue(newTx,Transaction[].class);
json错误：
No suitable constructor found for type [xxxx]: can not instantiate from JSON object (need to add/enable type information?) at xxx
这个需要java class中的内部类使用静态类，见transaction类中的output内部类。

后续复杂应用，再接着写。

Java 之利用OkHttpClient进行简单的http请求，利用Jackson框架把json转化为java对象的实现