我使用的net.sf.json是json-lib-2.4-jdk15.jar,把json对象转换为普通java实体对象时候有个问题，josn对象转换为java对象之后，json串里面的那几个小数点的值对应的java属性的值取不到。

json串如下所示:

{"Average":0.28,"Maximum":0.32,"Minimum":0.2,"instanceId":"i-426auf2hf","timestamp":1449938400000,"userId":"1467232540347717"}

java实体对象如下:

public class Model {    private double Average;    private double Maximum;    private double Minimum;    private String instanceId;    private long timestamp;    private String userId;    public double getAverage() {        return Average;    }    public void setAverage(double average) {        Average = average;    }    public double getMaximum() {        return Maximum;    }    public void setMaximum(double maximum) {        Maximum = maximum;    }    public double getMinimum() {        return Minimum;    }    public void setMinimum(double minimum) {        Minimum = minimum;    }    public String getInstanceId() {        return instanceId;    }    public void setInstanceId(String instanceId) {        this.instanceId = instanceId;    }    public long getTimestamp() {        return timestamp;    }    public void setTimestamp(long timestamp) {        this.timestamp = timestamp;    }    public String getUserId() {        return userId;    }    public void setUserId(String userId) {        this.userId = userId;    }}

转换代码如下:

JSONObject sfObject = JSONObject.fromObject(str);// 转换方法Model ecs = (Model) JSONObject.toBean(sfObject, Model.class);System.out.println(ecs.getAverage());

Average的值拿不到，所以输出的结果是:0.0,而不是0.28。

解决方案:

我放弃了json.lib,用google的Gson能够完美的解决。

Gson把json串转换成java实体对象的方法如下：

1.首页导入Gson的jar包，网上可以下载。

2. 实体类还是使用上面的实体类，转换代码如下所示:

String str = "{\"Average\":0.29,\"Maximum\":0.32,\"Minimum\":0.25,\"instanceId\":\"i-426auf2hf\",\"timestamp\":1449939900000,\"userId\":\"1467232540347717\"}";Model model = new Gson().fromJson(str, Model.class);System.out.println(model.getAverage());

使用Gson之后，打印结果正确。