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透過SerializeFilter可以使用擴充套件程式設計的方式實現定製序列化。fastjson提供了多種SerializeFilter：

PropertyPreFilter 根據PropertyName判斷是否序列化；PropertyFilter 根據PropertyName和PropertyValue來判斷是否序列化；NameFilter 修改Key，如果需要修改Key，process返回值則可；ValueFilter 修改Value；BeforeFilter 序列化時在最前新增內容；AfterFilter 序列化時在最後新增內容。

下面來看示例程式碼：

示例物件：

package json.fastjson.SerializeFilter;public class User {    private Long id;    private String name;    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    @Override    public String toString() {        return "User [id=" + id + ", name=" + name + "]";    }}12345678910111213141516171819202122232425262728

一、PropertyFilter 根據PropertyName和PropertyValue來判斷是否序列化

PropertyFilter 介面：

  public interface PropertyFilter extends SerializeFilter {      boolean apply(Object object, String propertyName, Object propertyValue);  }123

可以透過擴充套件實現根據object或者屬性名稱或者屬性值進行判斷是否需要序列化。例如：

package json.fastjson.SerializeFilter;import com.alibaba.fastjson.JSON;import com.alibaba.fastjson.serializer.PropertyFilter;public class TestPropertyFilter {    public static void main(String[] args) {        PropertyFilter filter = new PropertyFilter() {            @Override            public boolean apply(Object source, String name, Object value) {                System.out.println("----------------source=" + source);                System.out.println("----------------name=" + name);                System.out.println("----------------value=" + value);                System.out.println("");                // 屬性是id並且大於等於100時進行序列化                if ("id".equals(name)) {                    long id = ((Long) value).longValue();                    return id >= 100;                }                return false;            }        };        User user = new User();        user.setId(9L);        user.setName("挖坑埋你");        String jsonString = JSON.toJSONString(user, filter); // 序列化的時候傳入filter        System.out.println("序列化,id=9：" + jsonString + "\n");        user.setId(200L);        jsonString = JSON.toJSONString(user, filter); // 序列化的時候傳入filter        System.out.println("序列化,id=200：" + jsonString);    }}12345678910111213141516171819202122232425262728293031323334353637383940

輸出結果：

----------------source=User [id=9, name=挖坑埋你]----------------name=id----------------value=9----------------source=User [id=9, name=挖坑埋你]----------------name=name----------------value=挖坑埋你序列化,id=9：{}----------------source=User [id=200, name=挖坑埋你]----------------name=id----------------value=200----------------source=User [id=200, name=挖坑埋你]----------------name=name----------------value=挖坑埋你序列化,id=200：{"id":200}

二、NameFilter 序列化時修改Key

NameFilter 介面：

public interface NameFilter extends SerializeFilter {    String process(Object object, String propertyName, Object propertyValue);}123

如果需要修改Key，process返回值則可，例如：

package json.fastjson.SerializeFilter;import com.alibaba.fastjson.JSON;import com.alibaba.fastjson.serializer.NameFilter;import com.alibaba.fastjson.serializer.PascalNameFilter;public class TestNameFilter {    public static void main(String[] args) {        User user = new User();        user.setId(9L);        user.setName("挖坑埋你");        String jsonString = JSON.toJSONString(user); // 序列化的時候傳入filter        System.out.println("普通序列化：" + jsonString + "\n");        NameFilter filter = new NameFilter() {            @Override            public String process(Object object, String name, Object value) {                System.out.println("----------------object=" + object);                System.out.println("----------------name=" + name);                System.out.println("----------------value=" + value);                System.out.println("");                // 屬性是id是修改id的名字                if ("id".equals(name)) {                    return name + "$";                }                return name;            }        };        jsonString = JSON.toJSONString(user, filter); // 序列化的時候傳入filter        System.out.println("NameFilter序列化：" + jsonString + "\n");        // fastjson內建一個PascalNameFilter，用於輸出將首字元大寫的Pascal風格        jsonString = JSON.toJSONString(user, new PascalNameFilter()); // 序列化的時候傳入filter        System.out.println("PascalNameFilter序列化：" + jsonString + "\n");    }}

輸出結果：

普通序列化：{"id":9,"name":"挖坑埋你"}----------------object=User [id=9, name=挖坑埋你]----------------name=id----------------value=9----------------object=User [id=9, name=挖坑埋你]----------------name=name----------------value=挖坑埋你NameFilter序列化：{"id$":9,"name":"挖坑埋你"}PascalNameFilter序列化：{"Id":9,"Name":"挖坑埋你"}12345678910111213

三、ValueFilter 序列化時修改Value

ValueFilter 介面：

  public interface ValueFilter extends SerializeFilter {      Object process(Object object, String propertyName, Object propertyValue);  }123

如果需要修改Value，process返回值則可，例如：

package json.fastjson.SerializeFilter;import com.alibaba.fastjson.JSON;import com.alibaba.fastjson.serializer.ValueFilter;public class TestValueFilter {    public static void main(String[] args) {        User user = new User();        user.setId(9L);        user.setName("挖坑埋你");        String jsonString = JSON.toJSONString(user); // 序列化的時候傳入filter        System.out.println("普通序列化：" + jsonString + "\n");        ValueFilter filter = new ValueFilter() {            @Override            public Object process(Object object, String name, Object value) {                System.out.println("----------------object=" + object);                System.out.println("----------------name=" + name);                System.out.println("----------------value=" + value);                System.out.println("");                // 屬性是id時修改id的值                if ("id".equals(name)) {                    long id = ((Long) value).longValue();                    return id + "$";                }                return value;            }        };        jsonString = JSON.toJSONString(user, filter); // 序列化的時候傳入filter        System.out.println("ValueFilter序列化：" + jsonString + "\n");    }}12345678910111213141516171819202122232425262728293031323334353637

輸出結果：

普通序列化：{"id":9,"name":"挖坑埋你"}----------------object=User [id=9, name=挖坑埋你]----------------name=id----------------value=9----------------object=User [id=9, name=挖坑埋你]----------------name=name----------------value=挖坑埋你ValueFilter序列化：{"id":"9$","name":"挖坑埋你"}1234567891011

四、BeforeFilter 序列化時在最前新增內容

BeforeFilter 介面：

  public abstract class BeforeFilter implements SerializeFilter {      protected final void writeKeyValue(String key, Object value) { ... }      // 需要實現的抽象方法，在實現中呼叫writeKeyValue新增內容      public abstract void writeBefore(Object object);  }

在序列化物件的所有屬性之前執行某些操作，例如呼叫 writeKeyValue 新增內容：

package json.fastjson.SerializeFilter;import com.alibaba.fastjson.JSON;import com.alibaba.fastjson.serializer.BeforeFilter;public class TestBeforeFilter {    public static void main(String[] args) {        User user = new User();        user.setId(9L);        user.setName("挖坑埋你");        String jsonString = JSON.toJSONString(user); // 序列化的時候傳入filter        System.out.println("普通序列化：" + jsonString + "\n");        BeforeFilter filter = new BeforeFilter() {            @Override            public void writeBefore(Object object) {                System.out.println("----------------object=" + object);                User user = (User) object;                System.out.println("----------------User.id=" + user.getId() + " " + "User.name=" + user.getName() + "\n");                user.setName(user.getName() + "$$$");            }        };        jsonString = JSON.toJSONString(user, filter); // 序列化的時候傳入filter        System.out.println("BeforeFilter序列化：" + jsonString + "\n");    }}

輸出結果：

普通序列化：{"id":9,"name":"挖坑埋你"}----------------object=User [id=9, name=挖坑埋你]----------------User.id=9 User.name=挖坑埋你BeforeFilter序列化：{"id":9,"name":"挖坑埋你$$$"}123456

五、AfterFilter 序列化時在最後新增內容

AfterFilter 介面：

  public abstract class AfterFilter implements SerializeFilter {      protected final void writeKeyValue(String key, Object value) { ... }      // 需要實現的抽象方法，在實現中呼叫writeKeyValue新增內容      public abstract void writeAfter(Object object);  }12345

在序列化物件的所有屬性之後執行某些操作,例如呼叫 writeKeyValue 新增內容，例如：

package json.fastjson.SerializeFilter;import com.alibaba.fastjson.JSON;import com.alibaba.fastjson.serializer.AfterFilter;public class TestAfterFilter {    public static void main(String[] args) {        User user = new User();        user.setId(9L);        user.setName("挖坑埋你");        String jsonString = JSON.toJSONString(user); // 序列化的時候傳入filter        System.out.println("普通序列化：" + jsonString + "\n");        AfterFilter filter = new AfterFilter() {            @Override            public void writeAfter(Object object) {                User user = (User) object;                System.out.println("------------User.id=" + user.getId() + " " + "User.name=" + user.getName() + "\n");                user.setName(user.getName() + "$$$");            }        };        jsonString = JSON.toJSONString(user, filter); // 序列化的時候傳入filter        System.out.println("AfterFilter序列化：" + jsonString + "\n");        System.out.println(user);    }}

輸出結果：

普通序列化：{"id":9,"name":"挖坑埋你"}------------User.id=9 User.name=挖坑埋你AfterFilter序列化：{"id":9,"name":"挖坑埋你"}User [id=9, name=挖坑埋你$$$]